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  Subjects -> WATER RESOURCES (Total: 145 journals)
Showing 1 - 47 of 47 Journals sorted alphabetically
Acque Sotterranee     Open Access  
Acta Limnologica Brasiliensia     Open Access   (Followers: 2)
Advances in Oceanography and Limnology     Open Access   (Followers: 8)
Advances in Water Resource and Protection     Open Access   (Followers: 5)
Advances in Water Resources     Hybrid Journal   (Followers: 25)
African Journal of Aquatic Science     Hybrid Journal   (Followers: 12)
Agricultural Water Management     Hybrid Journal   (Followers: 21)
American Journal of Water Resources     Open Access   (Followers: 3)
American Water Works Association     Hybrid Journal   (Followers: 18)
Anales de Hidrología Médica     Open Access  
Annals of Warsaw University of Life Sciences - SGGW. Land Reclamation     Open Access  
Annual Review of Marine Science     Full-text available via subscription   (Followers: 9)
Applied Water Science     Open Access   (Followers: 5)
Aquacultural Engineering     Hybrid Journal   (Followers: 6)
Aquaculture     Hybrid Journal   (Followers: 30)
Aquaculture Environment Interactions     Open Access   (Followers: 1)
Aquaculture Research     Hybrid Journal   (Followers: 29)
Aquatic Conservation Marine and Freshwater Ecosystems     Hybrid Journal   (Followers: 32)
Aquatic Geochemistry     Hybrid Journal   (Followers: 2)
Aquatic Living Resources     Hybrid Journal   (Followers: 10)
Aquatic Procedia     Open Access  
Aquatic Science and Technology     Open Access   (Followers: 3)
Aquatic Sciences     Hybrid Journal   (Followers: 12)
Asian Journal of Earth Sciences     Open Access   (Followers: 19)
Asian Journal of Rural Development     Open Access   (Followers: 7)
Australian Journal of Water Resources     Full-text available via subscription   (Followers: 6)
Canadian Water Resources Journal     Hybrid Journal   (Followers: 17)
Civil and Environmental Research     Open Access   (Followers: 15)
CLEAN - Soil, Air, Water     Hybrid Journal   (Followers: 16)
Computational Water, Energy, and Environmental Engineering     Open Access   (Followers: 4)
Cost Effectiveness and Resource Allocation     Open Access   (Followers: 5)
Desalination     Hybrid Journal   (Followers: 6)
Desalination and Water Treatment     Hybrid Journal   (Followers: 8)
Developments in Water Science     Full-text available via subscription   (Followers: 8)
Ecological Chemistry and Engineering S     Open Access   (Followers: 2)
Environmental Science : Water Research & Technology     Full-text available via subscription   (Followers: 1)
Environmental Toxicology     Hybrid Journal   (Followers: 7)
EQA - International Journal of Environmental Quality     Open Access   (Followers: 1)
European journal of water quality - Journal européen d'hydrologie     Full-text available via subscription   (Followers: 5)
Ground Water Monitoring & Remediation     Hybrid Journal   (Followers: 15)
Grundwasser     Hybrid Journal  
Human Resources for Health     Open Access   (Followers: 7)
Hydro Nepal : Journal of Water, Energy and Environment     Open Access   (Followers: 3)
Hydrology Research     Partially Free   (Followers: 10)
Hydrology: Current Research     Open Access   (Followers: 9)
IDA Journal of Desalination and Water Reuse     Hybrid Journal  
Ingeniería del agua     Open Access  
International Journal of Climatology     Hybrid Journal   (Followers: 19)
International Journal of Hydrology Science and Technology     Hybrid Journal   (Followers: 4)
International Journal of Nuclear Desalination     Hybrid Journal  
International Journal of River Basin Management     Hybrid Journal   (Followers: 2)
International Journal of Salt Lake Research     Hybrid Journal   (Followers: 2)
International Journal of Waste Resources     Open Access   (Followers: 3)
International Journal of Water     Hybrid Journal   (Followers: 12)
International Journal of Water Resources and Environmental Engineering     Open Access   (Followers: 6)
International Journal of Water Resources Development     Hybrid Journal   (Followers: 20)
International Soil and Water Conservation Research     Open Access  
Irrigation and Drainage     Hybrid Journal   (Followers: 8)
Irrigation Science     Hybrid Journal   (Followers: 3)
Journal of Aquatic Sciences     Full-text available via subscription   (Followers: 2)
Journal of Contemporary Water Resource & Education     Hybrid Journal   (Followers: 3)
Journal of Environmental Health Science & Engineering     Open Access   (Followers: 1)
Journal of Fisheries and Aquatic Science     Open Access   (Followers: 5)
Journal of Geophysical Research : Oceans     Partially Free   (Followers: 14)
Journal of Hydro-environment Research     Full-text available via subscription   (Followers: 7)
Journal of Hydroinformatics     Full-text available via subscription   (Followers: 1)
Journal of Hydrology (New Zealand)     Full-text available via subscription   (Followers: 1)
Journal of Hydrology and Hydromechanics     Open Access   (Followers: 1)
Journal of Hydrometeorology     Full-text available via subscription   (Followers: 4)
Journal of Limnology     Open Access   (Followers: 6)
Journal of the American Water Resources Association     Hybrid Journal   (Followers: 25)
Journal of Water and Climate Change     Partially Free   (Followers: 28)
Journal of Water and Health     Partially Free   (Followers: 3)
Journal of Water Chemistry and Technology     Hybrid Journal   (Followers: 8)
Journal of Water Process Engineering     Full-text available via subscription   (Followers: 4)
Journal of Water Resource and Hydraulic Engineering     Open Access   (Followers: 6)
Journal of Water Resource and Protection     Open Access   (Followers: 9)
Journal of Water Resource Engineering and Management     Full-text available via subscription   (Followers: 2)
Journal of Water Resources Planning and Management     Full-text available via subscription   (Followers: 35)
Journal of Water Reuse and Desalination     Partially Free   (Followers: 6)
Journal of Water Security     Open Access   (Followers: 1)
Journal of Water Supply : Research and Technology - Aqua     Partially Free   (Followers: 7)
Journal of Water, Sanitation and Hygiene for Development     Open Access   (Followers: 4)
La Houille Blanche     Full-text available via subscription   (Followers: 1)
Lake and Reservoir Management     Hybrid Journal   (Followers: 6)
Lakes & Reservoirs Research & Management     Hybrid Journal   (Followers: 14)
Large Marine Ecosystems     Full-text available via subscription  
Liquid Waste Recovery     Open Access  
Mangroves and Salt Marshes     Hybrid Journal   (Followers: 2)
Marine and Freshwater Behaviour and Physiology     Hybrid Journal   (Followers: 1)
Marine Ecosystem Stressor Response     Open Access  
Methods in Oceanography : An International Journal     Hybrid Journal   (Followers: 1)
New Zealand Journal of Marine and Freshwater Research     Hybrid Journal   (Followers: 6)
Open Journal of Modern Hydrology     Open Access   (Followers: 3)
Osterreichische Wasser- und Abfallwirtschaft     Hybrid Journal  
Ozone Science & Engineering     Hybrid Journal   (Followers: 1)
Paddy and Water Environment     Hybrid Journal   (Followers: 6)
Research Journal of Environmental Toxicology     Open Access   (Followers: 2)
Reviews in Aquaculture     Hybrid Journal   (Followers: 9)
Revue des sciences de l'eau / Journal of Water Science     Full-text available via subscription   (Followers: 2)
RIBAGUA - Revista Iberoamericana del Agua     Open Access  
Riparian Ecology and Conservation     Open Access   (Followers: 5)
River Research and Applications     Hybrid Journal   (Followers: 14)
River Systems     Full-text available via subscription   (Followers: 3)
SA Irrigation = SA Besproeiing     Full-text available via subscription  
SABI Magazine - Tydskrif     Full-text available via subscription  
San Francisco Estuary and Watershed Science     Open Access   (Followers: 1)
Sciences Eaux & Territoires : la Revue du Cemagref     Open Access  
Scientia Marina     Open Access   (Followers: 2)
Society & Natural Resources: An International Journal     Hybrid Journal   (Followers: 13)
Sri Lanka Journal of Aquatic Sciences     Open Access   (Followers: 1)
Sustainability of Water Quality and Ecology     Hybrid Journal   (Followers: 2)
Sustainable Technologies, Systems & Policies     Open Access   (Followers: 9)
Tecnología y Ciencias del Agua     Open Access  
Texas Water Journal     Open Access   (Followers: 2)
Urban Water Journal     Hybrid Journal   (Followers: 13)
Water     Open Access   (Followers: 6)
Water & Sanitation Africa     Full-text available via subscription   (Followers: 3)
Water and Environment Journal     Hybrid Journal   (Followers: 16)
Water Environment and Technology     Full-text available via subscription   (Followers: 16)
Water Environment Research     Full-text available via subscription   (Followers: 35)
Water International     Hybrid Journal   (Followers: 10)
Water Policy     Partially Free   (Followers: 7)
Water Practice     Full-text available via subscription   (Followers: 3)
Water Practice and Technology     Full-text available via subscription   (Followers: 13)
Water Quality Research Journal of Canada     Full-text available via subscription   (Followers: 5)
Water Research     Hybrid Journal   (Followers: 42)
Water Resources     Hybrid Journal   (Followers: 15)
Water Resources and Economics     Hybrid Journal   (Followers: 3)
Water Resources and Industry     Open Access   (Followers: 3)
Water Resources and Rural Development     Hybrid Journal   (Followers: 1)
Water Resources Management     Hybrid Journal   (Followers: 20)
Water Resources Research     Full-text available via subscription   (Followers: 67)
Water SA     Open Access  
Water Science & Technology     Partially Free   (Followers: 20)
Water Science : The National Water Research Center Journal     Open Access   (Followers: 3)
Water Science and Engineering     Open Access   (Followers: 6)
Water Science and Technology : Water Supply     Partially Free   (Followers: 21)
Water Wheel     Open Access   (Followers: 2)
Water, Air, & Soil Pollution     Hybrid Journal   (Followers: 22)
Water21     Full-text available via subscription  
Waterlines     Full-text available via subscription   (Followers: 2)
Western Indian Ocean Journal of Marine Science     Open Access   (Followers: 1)
Wetlands Ecology and Management     Hybrid Journal   (Followers: 22)
Wiley Interdisciplinary Reviews : Water     Hybrid Journal  
WMU Journal of Maritime Affairs     Hybrid Journal   (Followers: 1)

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Journal Cover Water Resources Research
  [SJR: 2.189]   [H-I: 121]   [67 followers]  Follow
    
   Full-text available via subscription Subscription journal
   ISSN (Print) 0043-1397 - ISSN (Online) 1944-7973
   Published by American Geophysical Union (AGU) Homepage  [17 journals]
  • Photogrammetric discharge monitoring of small tropical mountain rivers: A
           case study at Rivière des Pluies, Rèunion island
    • Abstract: Reliable discharge measurements are indispensable for an effective management of natural water resources and floods. Limitations of classical current meter profiling and stage‐discharge ratings have stimulated the development of more accurate and efficient gauging techniques such as non‐intrusive photogrammetric techniques. Despite many successful applications of large‐scale particle image velocimetry (LSPIV) for short‐term measurements during flood events there are still very few studies that address its use for long‐term monitoring of small mountain rivers. To fill this gap this study targets the development and testing of largely autonomous photogrammetric discharge measurement system with a special focus on the application to small mountain river with high discharge variability in the tropics. It proposes several enhancements concerning camera calibration, more efficient processing in image geometry, the automatic detection of the water level as well as the statistical calibration and estimation of the discharge from multiple profiles. A case study which comprises the analysis of several thousand videos spanning over two and a half year is carried out to test the robustness and accuracy of different processing steps. Comparisons against classical current meter profiling show a mean absolute percentage error of 9.0% after the statistical calibration of the system. The study suggests that LSPIV can already be considered as a valuable tool for the monitoring of torrential flows, whereas further research is still needed to fully integrate night‐time observation and stereo‐photogrammetric capabilities. This article is protected by copyright. All rights reserved.
      PubDate: 2016-05-13T10:25:29.554123-05:
      DOI: 10.1002/2015WR018292
       
  • An intercomparison of remote sensing river discharge estimation algorithms
           from measurements of river height, width, and slope
    • Abstract: The Surface Water and Ocean Topography (SWOT) satellite mission planned for launch in 2020 will map river elevations and inundated area globally for rivers >100 m wide. In advance of this launch, we here evaluated the possibility of estimating discharge in ungauged rivers using synthetic, daily ‘remote sensing' measurements derived from hydraulic models corrupted with minimal observational errors. Five discharge algorithms were evaluated, as well as the median of the five, for nineteen rivers spanning a range of hydraulic and geomorphic conditions. Reliance upon a priori information, and thus applicability to truly ungauged reaches, varied among algorithms: one algorithm employed only global limits on velocity and depth, while the other algorithms relied on globally‐available prior estimates of discharge. We found at least one algorithm able to estimate instantaneous discharge to within 35% relative root mean squared error (RRMSE) on 14/16 non‐braided rivers despite out‐of‐bank flows, multi‐channel planforms, and backwater effects. Moreover, we found RRMSE was often dominated by bias; the median standard deviation of relative residuals across the 16 non‐braided rivers was only 12.5%. SWOT discharge algorithm progress is therefore encouraging, yet future efforts should consider incorporating ancillary data or multi‐algorithm synergy to improve results. This article is protected by copyright. All rights reserved.
      PubDate: 2016-05-13T10:25:25.873956-05:
      DOI: 10.1002/2015WR018434
       
  • On the choice of analogue fluids in CO2 convective dissolution experiments
    • Abstract: Mixtures of ethylene glycol and methanol (EG‐MeOH) have been used as an analogue system (i.e., EG‐MeOH/water) in recent experiments in the context of convective dissolution of CO2 in deep saline aquifers. We have conducted a linear stability analysis of a gravitationally unstable diffusive boundary layer as well as direct numerical simulation of convective mixing involved in dissolution of EG‐MeOH species in water. We provide new evidences that EG‐MeOH does not resemble the dynamics of convective instabilities and subsequent mixing associated with dissolution of CO2 in water. It is found that there are fundamental differences in the evolution of the buoyancy‐driven instability and dynamics of convective mixing between CO2/water and a typical EG‐MeOH/water analogue system. Our results show that for a constant Rayleigh number the onset of convective instabilities for EG‐MeOH/water can be different by an order of magnitude as compared with CO2/water. In addition, EG‐MeOH/water system reveals different dynamics associated with the convective mixing as compared to CO2/water system. This study improves our understanding of the instability behavior of analogue systems, their proper selection, and motivates further experiments. This article is protected by copyright. All rights reserved.
      PubDate: 2016-05-13T10:20:23.591359-05:
      DOI: 10.1002/2015WR018040
       
  • Effects of aridity in controlling the magnitude of runoff and erosion
           after wildfire
    • Authors: Philip J Noske; Patrick NJ Lane, Petter Nyman, Gary J Sheridan
      Abstract: This study represents a uniquely high resolution observation of post‐wildfire runoff and erosion from dry forested uplands of SE Australia. We monitored runoff and sediment load, and temporal changes in soil surface properties from two (0.2‐0.3 ha) dry forested catchments burned during the 2009 Black Saturday wildfire. Event‐based surface runoff to rainfall ratios approached 0.45 during the first year post‐wildfire, compared to reported values
      PubDate: 2016-05-11T19:05:26.255478-05:
      DOI: 10.1002/2015WR017611
       
  • Spectral‐induced polarization measurements on sieved sands and the
           relationship to permeability
    • Authors: Sheen Joseph; Malcolm Ingham, Gideon Gouws
      Abstract: Laboratory measurements of the permeability and spectral induced polarization (SIP) response of samples consisting of unconsolidated sands typical of those found in New Zealand aquifers have been made. After correction of measured formation factors to allow for the fact that some were measured at only one fluid conductivity, predictions of permeability from the grain size (d) of the samples are found to agree well with measured values of permeability. The Cole‐Cole time constant (derived from the SIP measurements) is found, as expected, to depend upon d2, but can be affected by the inclusion of smaller grains in the sample. Measurements made on samples comprising of mixtures of grain sizes show that inclusion in a sample of even 10% of smaller grains can significantly reduce both the Cole‐Cole time constant (τCC) and the permeability, and support theoretical derivation of how the permeability of a mixture of grain sizes varies with the content of the mixture. Proposed relationships for using τCC as a predictor for permeability are tested and found to be crucially dependent on the assumed relationship between the dynamic pore radius and grain size. The inclusion of a multiplicative constant to take account of numerical approximations results in good predictions for the permeability of the samples in this study. It seems unlikely, however, that there is a single global expression for predicting permeability from SIP data for all samples. This article is protected by copyright. All rights reserved.
      PubDate: 2016-05-09T10:56:35.619035-05:
      DOI: 10.1002/2015WR018087
       
  • Plant transpiration and groundwater dynamics in water‐limited
           climates: Impacts of hydraulic redistribution
    • Abstract: The role of groundwater in sustaining plant transpiration constitutes an important but not well understood aspect of the interactions between groundwater, the land surface, vegetation and the atmosphere. The effect of the hydraulic redistribution (HR) process by plant roots on the interplay between plant transpiration and groundwater dynamics under water‐limited climates is investigated by using the Variable Infiltration Capacity Plus (VIC+) land surface model. Numerical experiments, with or without explicitly considering HR, are conducted on soil columns over a range of groundwater table depths (GWTDs) under different vegetative land covers, soil types and precipitation conditions. When HR is not included, this study obtains transpiration – GWTD relationships consistent with those from watershed studies that do not include HR. When HR is included, the transpiration – GWTD relationships are modified. The modification introduced by HR is manifested in the soil moisture of the root zone. The mechanism of HR is explained by detailing the roles of the hydraulically redistributed water, the upward diffusion of soil water and the daytime root uptake. We have found that HR is particularly important in water‐limited climates under which plants have high transpiration demand. At the beginning stage of a dry period, HR modulates the severe impacts that climate has on plant transpiration. Only after a prolonged dry period, impacts of HR are lessened when the groundwater table drops below the depth of water uptake by roots and are diminished when plant transpiration is decoupled from groundwater dynamics. This article is protected by copyright. All rights reserved.
      PubDate: 2016-05-09T10:56:05.842225-05:
      DOI: 10.1002/2015WR017316
       
  • Assimilation of gridded terrestrial water storage observations from GRACE
           into a Land Surface Model
    • Abstract: Observations of terrestrial water storage (TWS) from the Gravity Recovery and Climate Experiment (GRACE) satellite mission have a coarse resolution in time (monthly) and space (roughly 150,000 km2 at mid‐latitudes) and vertically integrate all water storage components over land, including soil moisture and groundwater. Data assimilation can be used to horizontally downscale and vertically partition GRACE‐TWS observations. This work proposes a variant of existing ensemble‐based GRACE‐TWS data assimilation schemes. The new algorithm differs in how the analysis increments are computed and applied. Existing schemes correlate the uncertainty in the modeled monthly TWS estimates with errors in the soil moisture profile state variables at a single instant in the month and then apply the increment either at the end of the month or gradually throughout the month. The proposed new scheme first computes increments for each day of the month and then applies the average of those increments at the beginning of the month. The new scheme therefore better reflects sub‐monthly variations in TWS errors. The new and existing schemes are investigated here using gridded GRACE‐TWS observations. The assimilation results are validated at the monthly time‐scale, using in situ measurements of groundwater depth and soil moisture across the US. The new assimilation scheme yields improved (although not in a statistically significant sense) skill metrics for groundwater compared to the open‐loop (no assimilation) simulations and compared to the existing assimilation schemes. A smaller impact is seen for surface and root‐zone soil moisture, which have a shorter memory and receive smaller increments from TWS assimilation than groundwater. These results motivate future efforts to combine GRACE‐TWS observations with observations that are more sensitive to surface soil moisture, such as L‐band brightness temperature observations from Soil Moisture Ocean Salinity (SMOS) or Soil Moisture Active Passive (SMAP). Finally, we demonstrate that the scaling parameters that are applied to the GRACE observations prior to assimilation should be consistent with the land surface model that is used within the assimilation system. This article is protected by copyright. All rights reserved.
      PubDate: 2016-05-09T10:55:47.211764-05:
      DOI: 10.1002/2015WR018417
       
  • Reply to comments on “Climate and agricultural land use change
           impacts on streamflow in the upper Midwestern United States” by
           Schottler et al.
    • Authors: Satish C. Gupta; Andrew C. Kessler, Melinda K. Brown, William M. Schuh
      PubDate: 2016-05-06T10:15:26.970528-05:
      DOI: 10.1002/2016WR018827
       
  • Water temperature controls in low arctic rivers
    • Authors: Tyler V. King; Bethany T. Neilson, Levi D. Overbeck, Douglas L. Kane
      Abstract: Understanding the dynamics of heat transfer mechanisms is critical for forecasting the effects of climate change on arctic river temperatures. Climate influences on arctic river temperatures can be particularly important due to corresponding effects on nutrient dynamics and ecological responses. It was hypothesized that the same heat and mass fluxes affect arctic and temperate rivers, but that relative importance and variability over time and space differ. Through data collection and application of a river temperature model that accounts for the primary heat fluxes relevant in temperate climates, heat fluxes were estimated for a large arctic basin over wide ranges of hydrologic conditions. Heat flux influences similar to temperate systems included dominant shortwave radiation, shifts from positive to negative sensible heat flux with distance downstream, and greater influences of lateral inflows in the headwater region. Heat fluxes that differed from many temperate systems included consistently negative net longwave radiation and small average latent heat fluxes. Radiative heat fluxes comprised 88% of total absolute heat flux while all other heat fluxes contributed less than 5% on average. Periodic significance was seen for lateral inflows (up to 26%) and latent heat (up to 18%) in the lower and higher stream order portions of the watershed respectively. Evenly distributed lateral inflows from large scale flow differencing and temperatures from representative tributaries provided a data efficient method for estimating the associated heat loads. Poor model performance under low flows demonstrated need for further testing and data collection to support inclusion of additional heat fluxes. This article is protected by copyright. All rights reserved.
      PubDate: 2016-05-06T10:15:23.48825-05:0
      DOI: 10.1002/2015WR017965
       
  • Comment on “Climate and agricultural land use change impacts on
           streamflow in the upper Midwestern United States”
    • Authors: Shawn Schottler; Jason Ulrich, Daniel Engstrom
      PubDate: 2016-05-06T10:10:32.825478-05:
      DOI: 10.1002/2015WR018497
       
  • Wavelet‐based time series bootstrap model for multidecadal
           streamflow simulation using climate indicators
    • Authors: Solomon Tassew Erkyihun; Balaji Rajagopalan, Edith Zagona, Upmanu Lall, Kenneth Nowak
      Abstract: A model to generate stochastic streamflow projections conditioned on quasi‐oscillatory climate indices such as Pacific Decadal Oscillation (PDO) and Atlantic Multi‐decadal Oscillation (AMO) is presented. Recognizing that each climate index has underlying band‐limited components that contribute most of the energy of the signals, we first pursue a wavelet decomposition of the signals to identify and reconstruct these features from annually resolved historical data and proxy based paleo‐reconstructions of each climate index covering the period from 1650 to 2012. A K‐Nearest Neighbor block bootstrap approach is then developed to simulate the total signal of each of these climate index series while preserving its time‐frequency structure and marginal distributions. Finally, given the simulated climate signal time series, a K‐Nearest Neighbor bootstrap is used to simulate annual streamflow series conditional on the joint state space defined by the simulated climate index for each year. We demonstrate this method by applying it to simulation of streamflow at Lees Ferry gauge on the Colorado River using indices of two large scale climate forcings: Pacific Decadal Oscillation (PDO) and Atlantic Multi‐decadal Oscillation (AMO), which are known to modulate the Colorado River Basin (CRB) hydrology at multi‐decadal time scales. Skill in stochastic simulation of multi‐decadal projections of flow using this approach is demonstrated. This article is protected by copyright. All rights reserved.
      PubDate: 2016-05-06T10:10:31.83354-05:0
      DOI: 10.1002/2016WR018696
       
  • Tracking tracer motion in a 4‐D electrical resistivity tomography
           experiment
    • Authors: W. O. C. Ward; P. B. Wilkinson, J. E. Chambers, H. Nilsson, O. Kuras, L. Bai
      Abstract: A new framework for automatically tracking subsurface tracers in electrical resistivity tomography (ERT) monitoring images is presented. Using computer vision and Bayesian inference techniques, in the form of a Kalman filter, the trajectory of a subsurface tracer is monitored by predicting and updating a state model representing its movements. Observations for the Kalman filter are gathered using the maximally stable volumes algorithm, which is used to dynamically threshold local regions of an ERT image sequence to detect the tracer at each time‐step. The application of the framework to the results of 2‐D and 3‐D tracer monitoring experiments show that the proposed method is effective for detecting and tracking tracer plumes in ERT images in the presence of noise, without intermediate manual intervention. This article is protected by copyright. All rights reserved.
      PubDate: 2016-05-06T10:10:24.587144-05:
      DOI: 10.1002/2015WR017958
       
  • Using stochastic dual dynamic programming in problems with multiple
           near‐optimal solutions
    • Abstract: Stochastic dual dynamic programming (SDDP) is one of the few algorithmic solutions available to optimize large‐scale water resources systems while explicitly considering uncertainty. This paper explores the consequences of, and proposes a solution to, the existence of multiple near‐optimal solutions (MNOS) when using SDDP for mid‐ or long‐term river basin management. These issues arise when the optimization problem cannot be properly parametrized due to poorly defined and/or unavailable data sets. This work shows that when MNOS exists, 1) SDDP explores more than one solution trajectory in the same run, suggesting different decisions in distinct simulation years even for the same point in the state‐space, and 2) SDDP is shown to be very sensitive to even minimal variations of the problem setting, e.g. initial conditions ‐ we call this “algorithmic chaos”. Results that exhibit such sensitivity are difficult to interpret. This work proposes a re‐optimization method, which simulates system decisions by periodically applying cuts from one given year from the SDDP run. Simulation results obtained through this re‐optimization approach are steady‐state solutions, meaning that their probability distributions are stable from year to year. This article is protected by copyright. All rights reserved.
      PubDate: 2016-05-06T10:10:21.462064-05:
      DOI: 10.1002/2016WR018608
       
  • Acoustic mapping velocimetry
    • Authors: M. Muste; S. Baranya, R. Tsubaki, D. Kim, H. Ho, H. Tsai, D. Law
      Abstract: Knowledge of sediment dynamics in rivers is of great importance for various practical purposes. Despite its high relevance in riverine environment processes, the monitoring of sediment rates remains a major and challenging task for both suspended and bedload estimation. While the measurement of suspended load is currently an active area of testing with non‐intrusive technologies (optical and acoustic), bedload measurement does not mark a similar progress. This paper describes an innovative combination of measurement techniques and analysis protocols that establishes the proof‐of‐concept for a promising technique, labeled herein Acoustic Mapping Velocimetry (AMV). The technique estimates bedload rates in rivers developing bedforms using a non‐intrusive measurements approach. The raw information for AMV is collected with acoustic multi‐beam technology that in turn provides maps of the bathymetry over longitudinal swaths. As long as the acoustic maps can be acquired relatively quickly and the repetition rate for the mapping is commensurate with the movement of the bedforms, successive acoustic maps capture the progression of the bedform movement. Two‐dimensional velocity maps associated with the bedform migration are obtained by implementing algorithms typically used in particle image velocimetry to acoustic maps converted in gray‐level images. Furthermore, use of the obtained acoustic and velocity maps in conjunction with analytical formulations (e.g., Exner equation) enables estimation of multi‐directional bedload rates over the whole imaged area. This paper presents a validation study of the AMV technique using a set of laboratory experiments. This article is protected by copyright. All rights reserved.
      PubDate: 2016-05-05T03:51:32.545786-05:
      DOI: 10.1002/2015WR018354
       
  • Mapping permeability in low‐resolution micro‐CT images: A
           multiscale statistical approach
    • Authors: Pieter W.S.K. Botha; Adrian P. Sheppard
      Abstract: We investigate the possibility of predicting permeability in low‐resolution x‐ray micro‐computed tomography (µCT). Lower resolution whole core images give greater sample coverage and are therefore more representative of heterogeneous systems; however, the lower resolution causes connecting pore throats to be represented by intermediate gray scale values and limits information on pore system geometry, rendering such images inadequate for direct permeability simulation. We present an imaging and computation workflow aimed at predicting absolute permeability for sample volumes that are too large to allow direct computation. The workflow involves computing permeability from high‐resolution µCT images, along with a series of rock characteristics (notably open pore fraction, pore size and formation factor) from spatially registered low‐resolution images. Multiple linear regression models correlating permeability to rock characteristics provide a means of predicting and mapping permeability variations in larger scale low‐resolution images. Results show excellent agreement between permeability predictions made from 16 and 64 µm/voxel images of 25 mm diameter 80 mm tall core samples of heterogeneous sandstone for which 5 µm/voxel resolution is required to compute permeability directly. The statistical model used at the lowest resolution of 64 µm/voxel (similar to typical whole core image resolutions) includes open pore fraction and formation factor as predictor characteristics. Although binarized images at this resolution do not completely capture the pore system, we infer that these characteristics implicitly contain information about the critical fluid flow pathways. 3D permeability mapping in larger scale lower resolution images by means of statistical predictions lay the groundwork for permeability upscaling and the computation of effective permeability at the core scale. This article is protected by copyright. All rights reserved.
      PubDate: 2016-05-03T09:46:44.908826-05:
      DOI: 10.1002/2015WR018454
       
  • Temporal and spatial dynamics of large lake hypoxia: Integrating
           statistical and three‐dimensional dynamic models to enhance lake
           management criteria
    • Authors: Serghei A. Bocaniov; Donald Scavia
      Abstract: Hypoxia or low bottom water dissolved oxygen (DO) is a world‐wide problem of management concern requiring an understanding and ability to monitor and predict its spatial and temporal dynamics. However, this is often made difficult in large lakes and coastal oceans because of limited spatial and temporal coverage of field observations. We used a calibrated and validated three‐dimensional ecological model of Lake Erie to extend a statistical relationship between hypoxic extent and bottom water DO concentrations to explore implications of the broader temporal and spatial development and dissipation of hypoxia. We provide the first numerical demonstration that hypoxia initiates in the nearshore, not the deep portion of the basin, and that the threshold used to define hypoxia matters in both spatial and temporal dynamics and in its sensitivity to climate. We show that existing monitoring programs likely underestimate both maximum hypoxic extent and the importance of low oxygen in the nearshore, discuss implications for ecosystem and drinking water protection, and recommend how these results could be used to efficiently and economically extend monitoring programs. This article is protected by copyright. All rights reserved.
      PubDate: 2016-05-03T09:46:21.008341-05:
      DOI: 10.1002/2015WR018170
       
  • Testing the ability of a semidistributed hydrological model to simulate
           contributing area
    • Authors: SG. Mengistu; C. Spence
      Abstract: A dry climate, the prevalence of small depressions, and the lack of a well‐developed drainage network are characteristics of environments with extremely variable contributing areas to runoff. These types of regions arguably present the greatest challenge to properly understanding catchment streamflow generation processes. Previous studies have shown that contributing area dynamics are important for streamflow response, but the nature of the relationship between the two is not typically understood. Furthermore, it is not often tested how well hydrological models simulate contributing area. In this study, the ability of a semi‐distributed hydrological model, the PDMROF configuration of Environment Canada's MESH model, was tested to determine if it could simulate contributing area. The study focused on the St. Denis Creek watershed in central Saskatchewan, Canada, which with its considerable topographic depressions, exhibits wide variation in contributing area, making it ideal for this type of investigation. MESH‐PDMROF was able to replicate contributing area derived independently from satellite imagery. Daily model simulations revealed a hysteretic relationship between contributing area and streamflow not apparent from the less frequent remote sensing observations. This exercise revealed that contributing area extent can be simulated by a semi‐distributed hydrological model with a scheme that assumes storage capacity distribution can be represented with a probability function. However, further investigation is needed to determine if it can adequately represent the complex relationship between streamflow and contributing area that is such a key signature of catchment behaviour. This article is protected by copyright. All rights reserved.
      PubDate: 2016-05-03T09:41:17.559613-05:
      DOI: 10.1002/2016WR018760
       
  • Capture zone delineation methodology based on the maximum
           concentration—Preventative groundwater well protection areas for
           heat exchange fluid mixtures
    • Authors: Jarkko Okkonen; Roseanna M. Neupauer
      Abstract: Capture zones of water supply wells are most often delineated based on travel times of water or solute to the well, with the assumption that if the travel time is sufficiently large, the concentration of chemical at the well will not exceed the drinking water standards. In many situations, the likely source concentrations or release masses of contamination from the potential sources are unknown; therefore, the exact concentration at the well cannot be determined. In situations in which the source mass can be estimated with some accuracy, the delineation of the capture zone should be based on the maximum chemical concentration that can be expected at the well, rather than on an arbitrary travel time. We present a new capture zone delineation methodology that is based on this maximum chemical concentration. The method delineates capture zones by solving the adjoint of the advection‐dispersion‐reaction equation and relating the adjoint state and the known release mass to the expected chemical concentration at the well. We demonstrate the use of this method through a case study in which soil heat exchange systems are potential sources of contamination. The heat exchange fluid mixtures contain known fluid volumes and chemical concentrations; thus, in the event of a release, the release mass of the chemical is known. We also demonstrate the use of a concentration basis in quantifying other measures of well vulnerability including exposure time and time to exceed a predefined threshold concentration at the well. This article is protected by copyright. All rights reserved.
      PubDate: 2016-05-03T09:40:57.991118-05:
      DOI: 10.1002/2016WR018715
       
  • Sources and interpretation of channel complexity in forested subalpine
           streams of the Southern Rocky Mountains
    • Authors: Bridget Livers; Ellen Wohl
      Abstract: We evaluate correlations between stream geomorphic complexity and characteristics of the adjacent riparian forest, valley geometry, and land use history in forested subalpine streams of the Colorado Front Range. Measures of geomorphic complexity focus on cross‐sectional, planform, and instream wood piece and logjam variables. We categorize adjacent riparian forests as old‐growth unmanaged forest (OU), younger unmanaged forest (YU), and younger managed forest (YM), and valley geometry as laterally confined, partly confined, or unconfined. Significant differences in geomorphic stream complexity between OU, YU, and YM result primarily from differences in wood pieces and logjams, and these differences correlate strongly with pool volume and organic matter storage. Significant differences in planform and cross‐sectional complexity correlate more strongly with valley geometry, but do not explain as much of the observed variability in complexity between streams as do the wood variables. Unconfined OU streams have the largest wood loads and the greatest complexity, whereas legacy effects of logging, tie‐drives, and channel simplification create lower complexity in YM streams, even relative to YU streams flowing through similarly‐aged forest. We find that management history of riparian forests exerts the strongest control on reduced functional stream channel complexity, regardless of riparian forest stand age. This article is protected by copyright. All rights reserved.
      PubDate: 2016-05-02T11:38:20.062903-05:
      DOI: 10.1002/2015WR018306
       
  • Scale invariance of subsurface flow patterns and its limitation
    • Authors: S. Hergarten; G. Winkler, S. Birk
      Abstract: Preferential flow patterns in the subsurface are of great importance for the availability and the quality of water resources. However, knowledge of their spatial structure is still behind their importance, so that understanding the nature of preferential flow patterns is a major issue in subsurface hydrology. Comparing the statistics of river catchment sizes and spring discharges we found that the morphology of preferential subsurface flow patterns is probably scale‐invariant and similar to that of dendritic river networks. This result is not limited to karstic aquifers where the occurrence of dendritic structures has been known at least qualitatively for a long time. The scale invariance even seems to be independent of the lithology of the aquifer. However, scale invariance of river patterns seems to be only limited by the continental scale, while scale invariance of subsurface flow patterns breaks down at much smaller scales. The upper limit of scale invariance in subsurface flow patterns is highly variable. We found a range from thousands of square kilometers for limestone aquifers down to less than one square kilometer in the weathered zone and debris accumulations of crystalline rocks. This article is protected by copyright. All rights reserved.
      PubDate: 2016-05-02T11:38:07.595374-05:
      DOI: 10.1002/2015WR017530
       
  • Hazard function analysis for flood planning under nonstationarity
    • Authors: Laura K. Read; Richard M. Vogel
      Abstract: The field of hazard function analysis (HFA) involves a probabilistic assessment of the ‘time to failure' or ‘return period', T, of an event of interest. HFA is used in epidemiology, manufacturing, medicine, actuarial statistics, reliability engineering, economics and elsewhere. For a stationary process, the probability distribution function (pdf) of the return period always follows an exponential distribution, the same is not true for nonstationary processes. When the process of interest, X, exhibits nonstationary behavior, HFA can provide a complementary approach to risk analysis with analytical tools particularly useful for hydrological applications. After a general introduction to HFA we describe a new mathematical linkage between the magnitude of the flood event, X, and its return period, T, for nonstationary processes. We derive the probabilistic properties of T for a nonstationary 1‐parameter exponential model of X, and then use both Monte‐Carlo simulation and HFA to generalize the behavior of T when X arises from a nonstationary 2‐parameter lognormal distribution. For this case, our findings suggest that a 2‐parameter Weibull distribution provides a reasonable approximation for the pdf of T. We document how HFA can provide an alternative approach to characterizing the probabilistic properties of both nonstationary flood series and the resulting pdf of T. This article is protected by copyright. All rights reserved.
      PubDate: 2016-05-02T11:37:45.778969-05:
      DOI: 10.1002/2015WR018370
       
  • Comment on “Is unique scaling of aquifer macrodispersivity supported
           by field data?” by A. Zech et al.
    • Authors: Shlomo P. Neuman
      PubDate: 2016-05-02T11:37:34.912117-05:
      DOI: 10.1002/2016WR018636
       
  • Reply to comment by S. Neuman on “Is unique scaling of aquifer
           macrodispersivity supported by field data?”
    • Authors: A. Zech; S. Attinger, V. Cvetkovic, G. Dagan, P. Dietrich, A. Fiori, Y. Rubin, G. Teutsch
      PubDate: 2016-05-02T11:37:25.381597-05:
      DOI: 10.1002/2016WR018812
       
  • Revisiting hydraulic hysteresis based on long term monitoring of hydraulic
           states in lysimeters
    • Abstract: Hysteretic processes have been recognized for decades as an important characteristic of soil hydraulic behaviour. Several studies confirmed that wetting and drying periods cannot be described by a simple functional relationship, and that some non‐equilibrium of the water retention characteristics has to be taken into account. A large number of models describing the hysteresis of the soil water retention characteristic were successfully tested on soil cores under controlled laboratory conditions. However, its relevance under field conditions under natural forcings has rarely been investigated. In practice, the modeling of field soils usually neglects the hysteretic nature of soil hydraulic properties. In this study, long‐term observations of water content and matric potential in lysimeters of the lysimeter network TERENO‐SoilCan are presented, clearly demonstrating the hysteretic behavior of field soils. We propose a classification into three categories related to different time scales. Based on synthetic and long term monitoring data, three different models of hysteresis (Mualem [1984], Parker and Lenhard [1987], Poulovassilis and Kargas [2000]) were applied to data sets showing different degrees of hysteresis. We found no single model to be superior to the others. The model ranking depended on the degree of hysteresis. All models were able to reflect the general structure of hysteresis in most cases but failed to reproduce the detailed trajectories of state variables especially under highly transient conditions. As an important result we found that the temporal dynamics of wetting and drying significantly affects these trajectories which should be accounted for in future model concepts. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-29T04:50:46.273205-05:
      DOI: 10.1002/2015WR018319
       
  • High‐resolution modeling of coastal freshwater discharge and glacier
           mass balance in the Gulf of Alaska watershed
    • Authors: J.P. Beamer; D.F. Hill, A. Arendt, G.E. Liston
      Abstract: A comprehensive study of the Gulf of Alaska (GOA) drainage basin was carried out to improve understanding of the coastal freshwater discharge (FWD) and glacier volume loss (GVL). Hydrologic processes during the period 1980‐2014 were modeled using a suite of physically based, spatially distributed weather, energy‐balance snow/ice melt, soil water balance, and runoff routing models at a high resolution (1 km horizontal grid; daily time step). Meteorological forcing was provided by the North American Regional Reanalysis (NARR), Modern Era Retrospective Analysis for Research and Applications (MERRA), and Climate Forecast System Reanalysis (CFSR) datasets. Streamflow and glacier mass balance modeled using MERRA and CFSR compared well with observations in four watersheds used for calibration in the study domain. However, only CFSR produced regional seasonal and long term trends in water balance that compared favorably with independent Gravity Recovery and Climate Experiment (GRACE) and airborne altimetry data. Mean annual runoff using CFSR was 760 km3 yr−1, 8% of which was derived from the long‐term removal of stored water from glaciers (glacier volume loss). The annual runoff from CFSR was partitioned into 63% snowmelt, 17% glacier ice melt, and 20% rainfall. Glacier runoff, taken as the sum of rainfall, snow and ice melt occurring each season on glacier surfaces, was 38% of the total seasonal runoff, with the remaining runoff sourced from non‐glacier surfaces. Our simulations suggests that existing GRACE solutions, previously reported to represent glacier mass balance alone, are actually measuring the full water budget of land and ice surfaces. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-27T18:41:24.67043-05:0
      DOI: 10.1002/2015WR018457
       
  • Ensemble forecasting of short‐term system scale irrigation demands
           using real time flow data and numerical weather predictions
    • Authors: Kushan C. Perera; Andrew W. Western, David E. Robertson, Biju George, Bandara Nawarathna
      Abstract: Irrigation demands fluctuate in response to weather variations and a range of irrigation management decisions, which creates challenges for water supply system operators. This paper develops a method for real‐time ensemble forecasting of irrigation demand and applies it to irrigation command areas of various sizes for lead times of 1 to 5 days. The ensemble forecasts are based on a deterministic time series model coupled with ensemble representations of the various inputs to that model. Forecast inputs include past flow, precipitation, and potential evapotranspiration. These inputs are variously derived from flow observations from a modernized irrigation delivery system; short‐term weather forecasts derived from numerical weather prediction models and observed weather data available from automatic weather stations. The predictive performance for the ensemble spread of irrigation demand was quantified using rank histograms, the mean continuous rank probability score (CRPS), the mean CRPS reliability and the temporal mean of the ensemble root mean squared error (MRMSE). The mean forecast was evaluated using root mean squared error (RMSE), Nash–Sutcliffe model efficiency (NSE) and bias. The NSE values for evaluation periods ranged between 0.96 (1 day lead time, whole study area) and 0.42 (5 days lead time, smallest command area). Rank histograms and comparison of MRMSE, mean CRPS, mean CRPS reliability and RMSE indicated that the ensemble spread is generally a reliable representation of the forecast uncertainty for short lead times but underestimates the uncertainty for long lead times. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-27T18:41:02.561197-05:
      DOI: 10.1002/2015WR018532
       
  • Acceleration of groundwater remediation by deep sweeps and vortex
           ejections induced by rapidly pulsed pumping
    • Authors: David M. Kahler; Zbigniew J. Kabala
      Abstract: One key limiting factor to groundwater remediation is contaminant sequestered in pores whose contents do not mix well with the bulk flow. Mixing between well‐connected (pores whose volume is flushed as water flows through the aquifer) and poorly‐connected pores (pores whose volume does not exchange readily when water flows through the aquifer) is of primary concern. Under steady flow, contaminants are effectively trapped in the poorly‐connected pores and are transferred only by molecular diffusion. This slow mixing process between pore types is a bottleneck to remediation. We present a novel rapidly pulsed pumping method that increases the mixing between these pore types. We do it in the context of pump‐and‐treat remediation because it is the most common remediation practice. In rapidly pulsed pumping, the increase in flow causes a deep sweep, which pushes the flow into poorly‐connected pores and sweeps out sequestered contaminants. The decrease in flow causes a vortex ejection, which causes the vortex within the poorly‐connected pore to emerge with contaminant. These actions are modeled with computational fluid mechanics to elucidate the individual mechanisms and determine how they function and interact. Cleanup of single and multiple poorly‐connected pore systems were simulated and show the acceleration possible. This technique can decrease the time and cost needed to remediate contaminated aquifers, which in the United States has been estimated to exceed $1 trillion. Since our rapidly pulsed pumping method enhances mixing between well‐ and poorly‐connected pores, it can be applied to other remediation schemes such as in situ methods. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-27T18:40:40.454549-05:
      DOI: 10.1002/2015WR017157
       
  • Inferring river bathymetry via Image‐to‐Depth Quantile
           Transformation (IDQT)
    • Authors: Carl J. Legleiter
      Abstract: Conventional, regression‐based methods of inferring depth from passive optical image data undermine the advantages of remote sensing for characterizing river systems. This study introduces and evaluates a more flexible framework, Image‐to‐Depth Quantile Transformation (IDQT), that involves linking the frequency distribution of pixel values to that of depth. In addition, a new image processing workflow involving deep water correction and Minimum Noise Fraction (MNF) transformation can reduce a hyperspectral data set to a single variable related to depth and thus suitable for input to IDQT. Applied to a gravel‐bed river, IDQT avoided negative depth estimates along channel margins and under‐predictions of pool depth. Depth retrieval accuracy (R2 = 0.79) and precision (0.27 m) were comparable to an established band ratio‐based method, although a small shallow bias (0.04 m) was observed. Several ways of specifying distributions of pixel values and depths were evaluated but had negligible impact on the resulting depth estimates, implying that IDQT was robust to these implementation details. In essence, IDQT uses frequency distributions of pixel values and depths to achieve an aspatial calibration; the image itself provides information on the spatial distribution of depths. The approach thus reduces sensitivity to misalignment between field and image data sets and allows greater flexibility in the timing of field data collection relative to image acquisition, a significant advantage in dynamic channels. IDQT also creates new possibilities for depth retrieval in the absence of field data if a model could be used to predict the distribution of depths within a reach. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-27T18:36:44.97602-05:0
      DOI: 10.1002/2016WR018730
       
  • Hydrological drivers of record‐setting water level rise on Earth's
           largest lake system
    • Authors: A.D. Gronewold; J. Bruxer, D. Durnford, J.P. Smith, A.H. Clites, F. Seglenieks, S.S. Qian, T.S. Hunter, V. Fortin
      Abstract: Between January 2013 and December 2014, water levels on Lake Superior and Lake Michigan‐Huron, the two largest lakes on Earth by surface area, rose at the highest rate ever recorded for a two‐year period beginning in January and ending in December of the following year. This historic event coincided with below‐average air temperatures and extensive winter ice cover across the Great Lakes. It also brought an end to a 15‐year period of persistently below‐average water levels on Lakes Superior and Michigan‐Huron that included several months of record‐low water levels. To differentiate hydrological drivers behind the recent water level rise, we developed a Bayesian Markov chain Monte Carlo (MCMC) routine for inferring historical estimates of the major components of each lake's water budget. Our results indicate that, in 2013, the water level rise on Lake Superior was driven by increased spring runoff and over‐lake precipitation. In 2014, reduced over‐lake evaporation played a more significant role in Lake Superior's water level rise. The water level rise on Lake Michigan‐Huron in 2013 was also due to above‐average spring runoff and persistent over‐lake precipitation, while in 2014, it was due to a rare combination of below‐average evaporation, above‐average runoff and precipitation, and very high inflow rates from Lake Superior through the St. Marys River. We expect, in future research, to apply our new framework across the other Laurentian1 Great Lakes, and to Earth's other large freshwater basins as well. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-27T18:35:47.273273-05:
      DOI: 10.1002/2015WR018209
       
  • Can PDSI inform extreme precipitation?: An exploration with a 500 year
           long paleoclimate reconstruction over the United States
    • Authors: Scott Steinschneider; Michelle Ho, Edward R. Cook, Upmanu Lall
      Abstract: This study explores whether it is possible to reconstruct the frequency of extreme precipitation occurrence across the contiguous United States (CONUS) using the Living Blended Drought Atlas (LBDA), a 500‐year paleoclimate reconstruction of the summer (June‐August) Palmer Drought Severity Index (PDSI). We first identify regions of the country where the LBDA may reflect the occurrence of extremes based on their seasonality and contribution to total annual moisture delivery. Correlation measures are used to assess the relationship between the frequencies of extreme precipitation occurrence and both the instrumental monthly PDSI and the annual LBDA estimated PDSI. Extreme precipitation is found to account for a large portion of total precipitation west of the Mississippi River and clusters in particular seasons (winter and summer), supporting a strong relationship with the LBDA without much information loss from the instrumental PDSI data. Dimension reduction techniques are used to explore the joint spatiotemporal structure of extreme precipitation occurrence and LBDA across the country. The primary modes of variability of the LBDA and extreme precipitation occurrence relate remarkably well for a region centered over the Southwest that exhibits an ENSO‐like time‐frequency structure. Generalized linear models (GLMs) are used to demonstrate the feasibility of reconstructing the annual extreme precipitation frequency over the 500‐year pre‐historic record at two sites in the Southwest and Southern Plains. GLM‐based reconstructions show a high degree of structured variability in the likelihood of extreme precipitation occurrences over the pre‐historic record. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-26T10:15:54.601661-05:
      DOI: 10.1002/2016WR018712
       
  • Impact of kinetic mass transfer on free convection in a porous medium
    • Authors: Chunhui Lu; Liangsheng Shi, Yiming Chen, Yueqing Xie, Craig T. Simmons
      Abstract: We investigate kinetic mass transfer effects on unstable density‐driven flow and transport processes by numerical simulations of a modified Elder problem. The first‐order dual‐domain mass transfer model coupled with a variable‐density‐flow model is employed to describe transport behaviour in porous media. Results show that in comparison to the no‐mass‐transfer case, a higher degree of instability and more unstable system is developed in the mass transfer case due to the reduced effective porosity and correspondingly a larger Rayleigh number (assuming permeability is independent on the mobile porosity). Given a constant total porosity, the magnitude of capacity ratio (i.e. immobile porosity/mobile porosity) controls the macroscopic plume profile in the mobile domain, while the magnitude of mass transfer timescale (i.e., the reciprocal of the mass transfer rate coefficient) dominates its evolution rate. The magnitude of capacity ratio plays an important role on the mechanism driving the mass flux into the aquifer system. Specifically, for a small capacity ratio, solute loading is dominated by the density‐driven transport, while with increasing capacity ratio local mass transfer dominated solute loading may occur at later times. At significantly large times, however, both mechanisms contribute comparably to solute loading. Sherwood Number could be a non‐monotonic function of mass transfer timescale due to complicated interactions of solute between source zone, mobile zone and immobile zone in the top boundary layer, resulting in accordingly a similar behaviour of the total mass. The initial assessment provides important insights into unstable density‐driven flow and transport in the presence of kinetic mass transfer. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-25T19:04:09.084372-05:
      DOI: 10.1002/2016WR018724
       
  • Modeling nonlinear responses of DOC transport in boreal catchments in
           Sweden
    • Authors: Ville Kasurinen; Knut Alfredsen, Anne Ojala, Jukka Pumpanen, Gesa A. Weyhenmeyer, Martyn N. Futter, Hjalmar Laudon, Frank Berninger
      Abstract: Stream water dissolved organic carbon (DOC) concentrations display high spatial and temporal variation in boreal catchments. Understanding and predicting these patterns is a challenge with great implications for water quality projections and carbon balance estimates. Although several biogeochemical models have been used to estimate stream water DOC dynamics, model biases common during both rain and snow melt driven events. The parsimonious DOC‐model, K‐DOC, with ten calibrated parameters, uses a non‐linear discharge and catchment water storage relationship including soil temperature dependencies of DOC release and consumption. K‐DOC was used to estimate the stream water DOC concentrations over five years for eighteen nested boreal catchments having total area of 68 km2 (varying from 0.04 to 67.9 km2). The model successfully simulated DOC concentrations during base flow conditions, as well as, hydrological events in catchments dominated by organic and mineral soils reaching NSEs from 0.46 to 0.76. Our semi‐mechanistic model was parsimonious enough to have all parameters estimated using statistical methods. We did not find any clear differences between forest and mire dominated catchments that could be explained by soil type or tree species composition. However, parameters controlling slow release and consumption of DOC from soil water behaved differently for small headwater catchments (less than 2 km2) than for those that integrate larger areas of different ecosystem types (10‐68 km2). Our results emphasize that it is important to account for non‐linear dependencies of both, soil temperature and catchment water storage, when simulating DOC dynamics of boreal catchments This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-25T19:03:55.980175-05:
      DOI: 10.1002/2015WR018343
       
  • Utilizing the state of ENSO as a means for season‐ahead predictor
           selection
    • Authors: Brian G. Zimmerman; Daniel J. Vimont, Paul J. Block
      Abstract: This paper introduces the Nino Index Phase Analysis (NIPA) framework for forecasting hydroclimatic variables on a seasonal timescale. Antecedent Sea Surface Temperatures (SSTs) are commonly used in statistical predictive frameworks for seasonal forecasting, however the typical approach of evaluating all the years on record in one bin (‘phase') does not often provide the level of skill required by decision makers. For many locations around the world, the most influential climate signal on the seasonal timescale is the El Nino Southern Oscillation (ENSO), and there are various indices used to capture the state of ENSO and provide this information. NIPA utilizes the state of ENSO to classify the years of record into four phases, operating under the hypothesis that ENSO itself is affecting the ‘mean state' of the atmospheric ‐ oceanic system, and relevant teleconnections depend on and must be selected within these mean states. A case study focused on spring precipitation over the Lower Colorado River Basin (LCRB) in Texas is chosen to illustrate NIPA's potential. Results show that correlations between wintertime SST fields and spring precipitation in the LCRB improve from 0.21 to 0.47 for the typical ‘one phase' and the NIPA ‘four phase' approach, respectively. Even greater improvements are seen across tercile‐based skill scores such as the Heidke Hit Skill Score and Ranked Probability Skill Score; skill is particularly strong for years exhibiting extreme wet or dry conditions. It also outperforms the North American Multi‐Model Ensemble predictions across the LCRB for the selected seasons. This is encouraging as improved predictability through NIPA may translate to better decision‐making for water managers. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-25T18:56:28.45626-05:0
      DOI: 10.1002/2015WR017644
       
  • Terrestrial freshwater lenses in stable riverine settings: Occurrence and
           controlling factors
    • Authors: Adrian D. Werner; Tariq Laattoe
      Abstract: Rivers in arid and semi‐arid regions often traverse saline aquifers, creating buoyant freshwater lenses in the adjoining riparian and floodplain zones. The occurrence of freshwater lenses where the river is otherwise gaining saline groundwater appears counterintuitive, given that both hydraulic and density forces act towards the river. In this paper, an analytical solution is presented that defines the extent of a stable, sharp‐interface terrestrial freshwater lens (in cross section) in a riverine environment that otherwise contains saline groundwater moving towards the river. The method is analogous to the situation of an island freshwater lens, except in the riverine setting, the saltwater is mobile and the lens is assumed to be stagnant. The solution characterizes the primary controlling factors of riverine freshwater lenses, which are larger for situations involving lower hydraulic conductivities and rates of saltwater discharge to the river. Deeper aquifers, more transmissive riverbeds, and larger freshwater‐saltwater density differences produce more extensive lenses. The analytical solution predicts the parameter combinations that preclude the occurrence of freshwater lenses. The utility of the solution as a screening method to predict the occurrence of terrestrial freshwater lenses is demonstrated by application to parameter ranges typical of the South Australian portion of the River Murray, where freshwater lenses occur in only a portion of the neighboring floodplains. Despite assumptions of equilibrium conditions and a sharp freshwater‐saltwater interface, the solution for predicting the occurrence of riverine freshwater lenses presented in this study has immediate relevance to the management of floodplains in which freshwater lenses are integral to biophysical conditions. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-25T18:56:07.451954-05:
      DOI: 10.1002/2015WR018346
       
  • A multivariate Copula‐based framework for dealing with Hazard
           Scenarios and Failure Probabilities
    • Authors: G. Salvadori; F. Durante, C. De Michele, M. Bernardi, L. Petrella
      Abstract: This paper is of methodological nature, and deals with the foundations of Risk Assessment. Several international guidelines have recently recommended to select appropriate/relevant Hazard Scenarios in order to tame the consequences of (extreme) natural phenomena. In particular, the scenarios should be multivariate, i.e. they should take into account the fact that several variables, generally not independent, may be of interest. In this work, it is shown how a Hazard Scenario can be identified in terms of (i) a specific geometry and (ii) a suitable probability level. Several scenarios, as well as a Structural approach, are presented, and due comparisons are carried out. In addition, it is shown how the Hazard Scenario approach illustrated here is well suited to cope with the notion of Failure Probability, a tool traditionally used for design and risk assessment in engineering practice. All the results outlined throughout the work are based on the Copula Theory, which turns out to be a fundamental theoretical apparatus for doing multivariate risk assessment: formulas for the calculation of the probability of Hazard Scenarios in the general multi‐dimensional case (d ≥ 2) are derived, and worthy analytical relationships among the probabilities of occurrence of Hazard Scenarios are presented. In addition, the Extreme Value and Archimedean special cases are dealt with, relationships between dependence ordering and scenario levels are studied, and a counter‐example concerning Tail Dependence is shown. Suitable indications for the practical application of the techniques outlined in the work are given, and two case studies illustrate the procedures discussed in the paper. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-25T18:55:43.452289-05:
      DOI: 10.1002/2015WR017225
       
  • A global analysis of the seaward salt marsh extent: The importance of
           tidal range
    • Authors: Thorsten Balke; Martin Stock, Kai Jensen, Tjeerd J. Bouma, Michael Kleyer
      Abstract: Despite the growing interest in ecosystem services provided by intertidal wetlands, we lack sufficient understanding of the processes that determine the seaward extent of salt marsh vegetation on tidal flats. With the present study, we aim to establish a globally valid demarcation between tidal flats and salt marsh vegetation in relation to tidal range. By comparing results from a regional GIS study with a global literature search on the salt marsh‐ tidal flat border, we are able to define the global critical elevation, above which salt marsh plants can grow in the intertidal zone. Moreover, we calculate inundation characteristics from global tide gauge records to determine inundation duration and frequency at this predicted salt marsh ‐ tidal flat border depending on tidal range. Our study shows that the height difference between the lowest elevation of salt‐marsh pioneer vegetation and mean high water increases logarithmically with tidal range when including macrotidal salt marshes. Hence, the potentially vegetated section of the tidal frame below mean high water does not proportionally increase with tidal range. The data analysis suggests that inundation frequency rather than duration defines the global lower elevational limit of vascular salt marsh plants on tidal flats. This is critical information to better estimate sea level rise and coastal change effects on lateral marsh development. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-25T09:49:27.855499-05:
      DOI: 10.1002/2015WR018318
       
  • Identification and quantification of redox and pH buffering processes in a
           heterogeneous, low carbonate aquifer during managed aquifer recharge
    • Authors: Simone Seibert; Olivier Atteia, S. Ursula Salmon, Adam Siade, Grant Douglas, Henning Prommer
      Abstract: Managed aquifer recharge of aerobic water into deep aquifers often induces the oxidation of pyrite, which can lead to groundwater acidification and metal mobilisation. As circumneutral pH is often maintained by the dissolution of sedimentary calcite or high injectant alkalinity little attention is generally paid to potential alternative pH buffering processes. In contrast, this study analysed water quality evolution from a 2 year long groundwater replenishment trial in an anaerobic, mostly carbonate free aquifer. While injection of aerobic, very low salinity water triggered pyrite oxidation, the comprehensive field data showed that in many aquifer zones pH was buffered without substantial release of inorganic carbon. A numerical analysis was performed to test and evaluate different conceptual models and suggested that either proton buffering or the dissolution of aluminosilicates, or a combination thereof, can explain the observed, rapid buffering at locations where carbonates were absent. In contrast to many previous managed aquifer recharge (MAR) studies, the oxidation of sedimentary pyrite by nitrate was found to be of minor importance or negligible. The study also highlights that the depositional history of the aquifer, and the associated differences in mineralogy and geochemistry, need to be considered when estimating groundwater quality evolution during the injection of various water types for aquifer replenishment or other management purposes. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-25T09:48:14.544007-05:
      DOI: 10.1002/2015WR017802
       
  • From conservative to reactive transport under diffusion‐controlled
           conditions
    • Abstract: We assess the possibility to use conservative transport information, such as that contained in transit time distributions, breakthrough curves and tracer tests, to predict non‐linear fluid‐rock interactions in fracture/matrix or mobile/immobile conditions. Reference simulated data are given by conservative and reactive transport simulations in several diffusive porosity structures differing by their topological organization. Reactions includes non‐linear kinetically‐controlled dissolution and desorption. Effective Multi‐Rate Mass Transfer models (MRMT) are calibrated solely on conservative transport information without pore topology information and provide concentration distributions on which effective reaction rates are estimated. Reference simulated reaction rates and effective reaction rates evaluated by MRMT are compared, as well as characteristic desorption and dissolution times. Although not exactly equal, these indicators remain very close whatever the porous structure, differing at most by 0.6% and 10% for desorption and dissolution. At shorter times, this close agreement arises from the fine characterization of the diffusive porosity close to the mobile zone that controls fast mobile‐diffusive exchanges. At intermediate to larger times, concentration gradients are strongly reduced by diffusion, and reactivity can be captured by a very limited number of rates. We conclude that effective models calibrated solely on conservative transport information like MRMT can accurately estimate monocomponent kinetically‐controlled non‐linear fluid‐rock interactions. Their relevance might extend to more advanced biogeochemical reactions because of the close representation of conservative concentration distributions, even by parsimonious models (e.g., MRMT with 3‐5 rates). We propose a methodology to estimate reactive transport from conservative transport in mobile‐immobile conditions. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-25T09:46:21.484295-05:
      DOI: 10.1002/2015WR018294
       
  • Valuing year‐to‐go hydrologic forecast improvements for a
           peaking hydropower system in the Sierra Nevada
    • Authors: David E. Rheinheimer; Roger C. Bales, Carlos A. Oroza, Jay R. Lund, Joshua H. Viers
      Abstract: We assessed the potential value of hydrologic forecasting improvements for a snow‐dominated high‐elevation hydropower system in the Sierra Nevada of California, using a hydropower optimization model. To mimic different forecasting skill levels for inflow time series, rest‐of‐year inflows from regression‐based forecasts were blended in different proportions with representative inflows from a spatially distributed hydrologic model. The statistical approach mimics the simpler, historical forecasting approach that is still widely used. Revenue was calculated using historical electricity prices, with perfect price foresight assumed. With current infrastructure and operations, perfect hydrologic forecasts increased annual hydropower revenue by $0.14 to $1.6 million, with lower values in dry years and higher values in wet years, or about $0.8 million (1.2%) on average, representing overall willingness‐to‐pay for perfect information. A second, sensitivity analysis found a wider range of annual revenue gain or loss using different skill levels in snow measurement in the regression‐based forecast, mimicking expected declines in skill as climate warms and historical snow measurements no longer represent current conditions. The value of perfect forecasts was insensitive to storage capacity for small and large reservoirs, relative to average inflow, and modestly sensitive to storage capacity with medium (current) reservoir storage. The value of forecasts is highly sensitive to powerhouse capacity, particularly for the range of capacities in the northern Sierra Nevada. The approach can be extended to multi‐reservoir, multi‐purpose systems to help guide investments in forecasting. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-22T08:49:15.452454-05:
      DOI: 10.1002/2015WR018295
       
  • Catchment‐scale and reach‐scale controls on the distribution
           and expectation of geomorphic channel adjustment
    • Authors: Peyton E. Lisenby; Kirstie Fryirs
      Abstract: Variability in channel function (behavior) can be assessed by characterizing different forms of adjustment over time. Here, historical channel adjustments in three tributary systems of the Lockyer Valley, Southeast Queensland (SEQ) are analyzed in order to evaluate the range of catchment‐ and reach‐scale controls on channel behavior. Over 300 individual adjustments and 13 forms of adjustment were identified over a ∼ 130 year time span. We measured the width‐to‐depth ratio (W:D), mean stream power (ω), and basin area (A) at the location of all observed adjustments. The most common forms of adjustment were avulsions, lateral expansion of the channel, and bend adjustments. The tributary systems behave distinctly different from one another according to statistical comparisons between the W:D, ω, and A data for these forms of adjustment. We find that it is possible to develop process domains or typologies for forms of geomorphic adjustment found in the Lockyer Valley. These domains or typologies provide the foundations for synoptic comparisons between catchments and assessing the expectation of channel adjustment (forecasting), which should be included in process‐based river management practice. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-22T07:16:06.719837-05:
      DOI: 10.1002/2015WR017747
       
  • Confined aquifer head measurements and storage properties in the San Luis
           Valley, Colorado, from spaceborne InSAR observations
    • Abstract: Interferometric synthetic aperture radar (InSAR), a remote sensing technique for measuring centimeter‐level surface deformation, is used to estimate hydraulic head in the confined aquifer of the San Luis Valley (SLV), Colorado. Reconstructing head measurements from InSAR in agricultural regions can be difficult, as InSAR phase data are often decorrelated due to vegetation growth. Analysis of 17 L‐band ALOS PALSAR scenes, acquired between January, 2007 and March, 2011, demonstrates that comprehensive InSAR deformation measurements can be recovered over the vegetated groundwater basin with an improved processing strategy. Local skeletal storage coefficients and time delays between the head change and deformation are estimated through a joint InSAR‐well data analysis. InSAR subsidence estimates are transformed to head changes with finer temporal and spatial resolution than is possible using existing well records alone. Both InSAR and well data suggest that little long‐term water‐storage loss occurred in the SLV over the study period and that inelastic compaction was negligible. The seasonal head variations derived from InSAR are consistent with the existing well data at most locations where confined aquifer pumping activity dominates. Our results demonstrate the advantages of InSAR measurements for basin‐wide characterization of aquifer storage properties and groundwater levels over agricultural regions. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-21T19:21:26.758254-05:
      DOI: 10.1002/2015WR018466
       
  • Water table‐dependent hydrological changes following peatland
           forestry drainage and restoration: Analysis of restoration success
    • Abstract: A before‐after‐control approach was used to analyze the impact of peatland restoration on hydrology, based on high temporal resolution water‐table (WT) data from 43 boreal peatlands representative of a south‐boreal to north‐boreal climate gradient. During the study, 24 forestry drained sites were restored and 19 pristine peatlands used as control sites. Different approaches were developed and used to analyze WT changes (mean WT position, WT fluctuation, WT hydrograph, recession, and storage characteristics). Restoration increased WT in most cases but particularly in spruce mires, followed by pine mires and fens. Before restoration, the WT fluctuation (WTF) was large, indicating peat temporary storage gain (SG). After restoration, the WT hydrograph recession limb slopes and SG coefficients (Rc) declined significantly. Drainage or restoration did not significantly affect mean diurnal WT fluctuations, used here as a proxy for evapotranspiration. Overall, the changes in WT characteristics following restoration indicated creation of favorable hydrological conditions for recovery of functional peatland ecosystems in previously degraded peatland sites. This was supported by calculation of bryophyte species abundance thresholds for WT. These results can be used to optimize restoration efforts in different peatland systems and as a qualitative conceptual basis for future restoration operations. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-21T19:20:48.232851-05:
      DOI: 10.1002/2015WR018578
       
  • Global‐scale regionalization of hydrologic model parameters
    • Authors: Hylke E. Beck; Albert I. J. M. van Dijk, Ad de Roo, Diego G. Miralles, Tim R. McVicar, Jaap Schellekens, L. Adrian Bruijnzeel
      Abstract: Current state‐of‐the‐art models typically applied at continental to global scales (hereafter called macro‐scale) tend to use a priori parameters, resulting in suboptimal streamflow (Q) simulation. For the first time, a scheme for regionalization of model parameters at the global scale was developed. We used data from a diverse set of 1787 small‐to‐medium sized catchments (10‐10000 km2) and the simple conceptual HBV model to set up and test the scheme. Each catchment was calibrated against observed daily Q, after which 674 catchments with high calibration and validation scores, and thus presumably good‐quality observed Q and forcing data, were selected to serve as donor catchments. The calibrated parameter sets for the donors were subsequently transferred to 0.5° grid cells with similar climatic and physiographic characteristics, resulting in parameter maps for HBV with global coverage. For each grid cell, we used the ten most similar donor catchments, rather than the single most similar donor, and averaged the resulting simulated Q, which enhanced model performance. The 1113 catchments not used as donors were used to independently evaluate the scheme. The regionalized parameters outperformed spatially‐uniform (i.e., averaged calibrated) parameters for 79% of the evaluation catchments. Substantial improvements were evident for all major Köppen‐Geiger climate types and even for evaluation catchments > 5000 km distant from the donors. The median improvement was about half of the performance increase achieved through calibration. HBV with regionalized parameters outperformed nine state‐of‐the‐art macro‐scale models, suggesting these might also benefit from the new regionalization scheme. The produced HBV parameter maps including ancillary data are available via http://water.jrc.ec.europa.eu/HBV/. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-20T18:06:13.217009-05:
      DOI: 10.1002/2015WR018247
       
  • Relation between grid, channel, and Peano networks in
           high‐resolution digital elevation models
    • Authors: Samuele De Bartolo; Francesco Dell'Accio, Giuseppe Frandina, Giovanni Moretti, Stefano Orlandini, Massimo Veltri
      Abstract: The topological interconnection between grid, channel, and Peano networks is investigated by extracting grid and channel networks from high‐resolution digital elevation models of real drainage basins, and by using a perturbed form of the equation describing how the average junction degree varies with Horton‐Strahler order in Peano networks. The perturbed equation is used to fit the data observed over the Hortonian substructures of real networks. The perturbation parameter, denoted as “uniformity factor,” is shown to indicate the degree of topological similarity between Hortonian and Peano networks. The sensitivities of computed uniformity factors and drainage densities to grid cell size and selected threshold for channel initiation are evaluated. While the topological relation between real and Peano networks may not vary significantly with grid cell size, these networks are found to exhibit the same drainage density only for specific grid cell sizes, which may depend on the selected threshold for channel initiation. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-20T18:00:48.833203-05:
      DOI: 10.1002/2015WR018076
       
  • A probabilistic formulation of bed load transport to include spatial
           variability of flow and surface grain size distributions
    • Authors: Angel Monsalve; Elowyn M. Yager, Jens M. Turowski, Dieter Rickenmann
      Abstract: Bed load fluxes are typically calculated as a function of the reach averaged boundary shear stress and a representative bed grain size distribution. In steep, rough channels, heterogeneous bed surface texture and macro‐roughness elements cause significant local deviations from the mean shear stress but this variability is often omitted in bed load calculations. Here we present a probabilistic bed load transport formulation that explicitly includes local variations in the flow field and grain size distribution. The model is then tested in a 10% gradient stream, to evaluate its predictive capability and to explore relations between surface grain size sorting and boundary shear stress. The boundary shear stress field, calculated using a quasi‐3D hydraulic model, displayed substantial variability between patch classes, but the patch mean dimensionless shear stress varied inversely with patch median grain size. We developed an empirical relation between the applied shear stress on each patch class and the reach averaged shear stress and median grain size. Predicted sediment volumes using this relation in our bed load equation were as accurate as those using complete shear stress distributions and more accurate than current bed load transport equations. Our results suggest that when spatially variable grain size distributions (e.g. patches of sediment) are present they must be explicitly included in bed load transport calculations. Spatial variability in shear stress was relatively more important than grain size variations for sediment transport predictions. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-20T10:46:07.493693-05:
      DOI: 10.1002/2015WR017694
       
  • Unlocking the full potential of Earth observation during the 2015 Texas
           flood disaster
    • Abstract: Intense rainfall during late April and early May 2015 in Texas and Oklahoma led to widespread and sustained flooding in several river basins. Texas state agencies relevant to emergency response were activated when severe weather then ensued for six weeks from May 8 until June 19 following Tropical Storm Bill. An international team of scientists and flood response experts assembled and collaborated with decision‐making authorities for user‐driven high resolution satellite acquisitions over the most critical areas; while experimental automated flood mapping techniques provided daily on‐going monitoring. This allowed mapping of flood inundation from an unprecedented number of space‐ and air‐borne images. In fact, a total of 27,174 images have been ingested to the USGS Hazards Data Distribution System (HDDS) Explorer, except for the SAR images used. Based on the Texas flood use case, we describe the success of this effort as well as the limitations in fulfilling the needs of the decision‐makers, and reflect upon these. In order to unlock the full potential for Earth observation data in flood disaster response, we suggest in a call for action (i) stronger collaboration from the onset between agencies, product developers and decision‐makers; (ii) quantification of uncertainties when combining data from different sources in order to augment information content; (iii) include a default role for the end‐user in satellite acquisition planning; and (iv) proactive assimilation of methodologies and tools into the mandated agencies. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-20T10:45:41.189053-05:
      DOI: 10.1002/2015WR018428
       
  • Modeling soil evaporation efficiency in a range of soil and atmospheric
           conditions using a meta‐analysis approach
    • Abstract: A meta‐analysis data‐driven approach is developed to represent the soil evaporative efficiency (SEE) defined as the ratio of actual to potential soil evaporation. The new model is tested across a bare soil database composed of more than 30 sites around the world, a clay fraction range of 0.02‐0.56, a sand fraction range of 0.05‐0.92, and about 30,000 acquisition times. SEE is modeled using a soil resistance (rss) formulation based on surface soil moisture (θ) and two resistance parameters rss,ref and θefolding. The data‐driven approach aims to express both parameters as a function of observable data including meteorological forcing, cut‐off soil moisture value θ1/2 at which SEE=0.5, and first derivative of SEE at θ1/2, named Δθ1/2−1. An analytical relationship between (rss,ref; θefolding) and (θ1/2; Δθ1/2−1) is first built by running a soil energy balance model for two extreme conditions with rss = 0 and rss ∼ ∞ using meteorological forcing solely, and by approaching the middle point from the two (wet and dry) references points. Two different methods are then investigated to estimate the pair (θ1/2; Δθ1/2−1) either from the time series of SEE and θ observations for a given site, or using the soil texture information for all sites. The first method is based on an algorithm specifically designed to accomodate for strongly nonlinear SEE(θ) relationships and potentially large random deviations of observed SEE from the mean observed SEE(θ). The second method parameterizes θ1/2 as a multilinear regression of clay and sand percentages, and sets Δθ1/2−1 to a constant mean value for all sites. The new model significantly outperformed the evaporation modules of ISBA (Interaction Sol‐Biosphére‐Atmosphére), H‐TESSEL (Hydrology‐Tiled ECMWF Scheme for Surface Exchange over Land), and CLM (Community Land Model). It has potential for integration in various land‐surface schemes, and real calibration capabilities using combined thermal and microwave remote sensing data. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-20T04:21:30.669361-05:
      DOI: 10.1002/2015WR018233
       
  • Channel morphology and flow structure of an abandoned channel under
           varying stages
    • Authors: Katie H. Costigan; Joseph E. Gerken
      Abstract: Abandoned channels are those channels left behind as meandering rivers migrate over their floodplains but remain among the most enigmatic features of the riverscape, especially related to their hydraulics and geomorphology. Abandoned channels are being considered and implemented as restoration and rehabilitation strategies for large rivers but we do not yet have a sound understanding of their hydromorphodynamics. The overall objectives of this work were to assess the bed morphology and flow structure of a large, dynamically connected abandoned channel (e.g., the channel is inundated during annual or decadal floods through bank overflow) under varying stages. Here we document the hydromorphodynamics of an abandoned channel during 3.4, 9.2, and 37.9 return interval discharges using an acoustic Doppler current profiler. Flow separation was observed along the channel entrance during the lowest flow surveying campaign but was not seen during the higher flow campaign. Width to depth ratio and channel width at the exit both progressively decreased from the first surveying campaign, despite the final campaign having the highest measured discharge. Large zones of flow stagnation and recirculation were observed, with depth averaged velocity vectors not aligning in one direction, in the abandoned channel where water from the entrance was meeting water coming up from the exit during moderate discharges. The abandoned channel has been maintained for at least 25 years due to its low diversion angle and it being perched above the Kansas River. Results of this study provide insights of how flow hydraulics and physical characteristics of abandoned channel change under varying stages. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-19T10:36:31.999154-05:
      DOI: 10.1002/2015WR017601
       
  • Vertical variation of mixing within porous sediment beds below turbulent
           flows
    • Authors: I.D. Chandler; I. Guymer, J.M. Pearson, R. van Egmond
      Abstract: River ecosystems are influenced by contaminants in the water column, in the pore water and adsorbed to sediment particles. When exchange across the sediment‐water interface (hyporheic exchange) is included in modelling, the mixing coefficient is often assumed to be constant with depth below the interface. Novel fibre‐optic fluorometers have been developed and combined with a modified EROSIMESS system to quantify the vertical variation in mixing coefficient with depth below the sediment‐water interface. The study considered a range of particle diameters and bed shear velocities, with the permeability Péclet number, between 1,000 and 77,000 and the shear Reynolds number, between 5 and 600. Different parameterisation of both an interface exchange coefficient and a spatially variable in‐sediment mixing coefficient are explored. The variation of in‐sediment mixing is described by an exponential function applicable over the full range of parameter combinations tested. The empirical relationship enables estimates of the depth to which concentrations of pollutants will penetrate into the bed sediment, allowing the region where exchange will occur faster than molecular diffusion to be determined. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-19T10:36:10.907817-05:
      DOI: 10.1002/2015WR018274
       
  • Valuing water resources in Switzerland using a hedonic price model
    • Authors: Diana van Dijk; Rosi Siber, Roy Brouwer, Ivana Logar, Dorsa Sanadgol
      Abstract: In this paper, linear and spatial hedonic price models are applied to the housing market in Switzerland, covering all 26 cantons in the country over the period 2005‐2010. Besides structural house, neighborhood and socio‐economic characteristics, we include a wide variety of new environmental characteristics related to water to examine their role in explaining variation in sales prices. These include water abundance, different types of water bodies, the recreational function of water and water disamenity. Significant spatial autocorrelation is found in the estimated models, as well as non‐linear effects for distances to the nearest lake and large river. Significant effects are furthermore found for water abundance and the distance to large rivers, but not to small rivers. Although in both linear and spatial models water related variables explain less than one percent of the price variation, the distance to the nearest bathing site has a larger marginal contribution than many neighborhood related distance variables. The housing market shows to differentiate between different water related resources in terms of relative contribution to house prices, which could help the housing development industry make more geographically targeted planning activities. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-19T10:35:43.031134-05:
      DOI: 10.1002/2015WR017534
       
  • The impact of land‐cover change on flood peaks in peatland basins
    • Authors: Jihui Gao; Joseph Holden, Mike Kirkby
      Abstract: In headwater peatlands, saturation‐excess overland flow is a dominant source of river discharge. Human modifications to headwater peatlands result in vegetation cover change but there is a lack of understanding about how the spatial distribution of such change impacts flood peaks. A fully distributed version of TOPMODEL with an overland flow velocity module was used to simulate flood response for three upland peat basins. Bare peat strips adjacent to channels resulted in a higher and faster flow peak; for a 20 mm/hr rainfall event, with bare riparian zones covering 10% of the basin area, peaks were increased, compared to the current hydrograph, by 12.8%, 1.8% and 19.6% in the three basins. High density Sphagnum ground cover over the same riparian zones reduced flow peaks (e.g. by 10.1%, 1.8% and 13.4% for the 20 mm hr−1 event) compared to the current hydrograph. With similar total areas of land‐cover change, the size of randomly located patches of changed cover had no effect on peak flow for patch sizes up to 40000 m2. However, cover changes on gentle slope areas generally resulted in a larger change in peak flow when compared with the same changes on steeper slopes. Considering all results for the same proportion of catchment area that undergoes change, land‐cover change along narrow riparian buffer strips had the highest impact on river flow. Thus, the protection and revegetation of damaged riparian areas in upland peat catchments may be highly beneficial for flood management. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-15T10:46:04.759807-05:
      DOI: 10.1002/2015WR017667
       
  • A critical evaluation of the Miller and Miller similar media theory for
           application to natural soils
    • Authors: Morteza Sadeghi; Bijan Ghahraman, Arthur W. Warrick, Markus Tuller, Scott B. Jones
      Abstract: The Miller‐Miller similar media theory is widely applied to characterize the spatial variability of soil hydraulic properties. For a group of soils a distinct scaling factor is commonly assigned to each individual soil to coalesce the soil water characteristic and hydraulic conductivity functions to single curves. It is generally assumed that the Miller‐Miller theory is valid as long as soils are “similar” either with regard to their microscopic pore space geometry or the closely related macroscopic soil hydraulic functions. In this paper it is illustrated that similarity is not the sole required condition for validity of the Miller‐Miller theory. In addition, the interrelation between the soil water characteristic and the hydraulic conductivity functions considered for scaling need to be comparable. The interrelation is dependent not only on the pore space geometry, but also on solid‐liquid interactions. Hence similar interrelation cannot be concluded from similarity of microscopic pore space geometry. A dimensionless parameter termed the “joint scaling factor” was defined and applied to evaluate the soundness of the interrelation condition for 26 soils from the UNSODA database that were grouped into 6 classes of similar soils. Obtained results clearly reveal the crucial importance of the interrelation condition for the Miller‐Miller scaling theory, which has been hidden behind the “similarity” requirement, and contradict the general belief that Miller‐Miller scaling is valid as long as soils are “similar”. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-15T10:45:42.44235-05:0
      DOI: 10.1002/2015WR017929
       
  • Comment on “Climate and agricultural land use change impacts on
           streamflow in the upper midwestern United States” by Satish C. Gupta
           et al.
    • Authors: Dingbao Wang
      PubDate: 2016-04-12T20:38:02.827375-05:
      DOI: 10.1002/2015WR018469
       
  • Time domain random walks for hydrodynamic transport in heterogeneous media
    • Authors: Anna Russian; Marco Dentz, Philippe Gouze
      Abstract: We derive a general formulation of the time domain random walk (TDRW) approach to model the hydrodynamic transport of inert solutes in complex geometries and heterogeneous media. We demonstrate its formal equivalence with the discretized advection‐dispersion equation and show that the TDRW is equivalent to a continuous time random walk (CTRW) characterized by space‐dependent transition times and transition probabilities. The transition times are exponentially distributed. We discuss the implementation of different concentration boundary conditions and initial conditions as well as the occurrence of numerical dispersion. Furthermore, we propose an extension of the TDRW scheme to account for mobile‐immobile multirate mass transfer. Finally, the proposed TDRW scheme is validated by comparison to analytical solutions for spatially homogeneous and heterogeneous transport scenarios. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-12T20:33:03.162746-05:
      DOI: 10.1002/2015WR018511
       
  • Value of long‐term streamflow forecasts to reservoir operations for
           water supply in snow‐dominated river catchments
    • Authors: D. Anghileri; N. Voisin, A. Castelletti, F. Pianosi, B. Nijssen, D.P. Lettenmaier
      Abstract: We present a forecast‐based adaptive management framework for water supply reservoirs and evaluate the contribution of long‐term inflow forecasts to reservoir operations. Our framework is developed for snow‐dominated river basins that demonstrate large gaps in forecast skill between seasonal and inter‐annual time horizons. We quantify and bound the contribution of seasonal and inter‐annual forecast components to optimal, adaptive reservoir operation. The framework uses an Ensemble Streamflow Prediction (ESP) approach to generate retrospective, one‐year‐long streamflow forecasts based on the Variable Infiltration Capacity (VIC) hydrology model. We determine the optimal sequence of daily release decisions using the Model Predictive Control (MPC) optimization scheme. We then assess the forecast value by comparing system performance based on the ESP forecasts with the performances based on climatology and perfect forecasts. We distinguish among the relative contributions of the seasonal component of the forecast versus the inter‐annual component by evaluating system performance based on hybrid forecasts, which are designed to isolate the two contributions. As an illustration, we first apply the forecast‐based adaptive management framework to a specific case study, i.e., Oroville Reservoir in California, then we modify the characteristics of the reservoir and the demand to demonstrate the transferability of the findings to other reservoir systems. Results from numerical experiments show that, on average, the overall ESP value in informing reservoir operation is 35% less than the perfect forecast value and the inter‐annual component of the ESP forecast contributes 20‐60% of the total forecast value. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-12T20:32:41.891472-05:
      DOI: 10.1002/2015WR017864
       
  • Recharge of low‐arsenic aquifers tapped by community wells in
           Araihazar, Bangladesh, inferred from environmental isotopes
    • Authors: I. Mihajlov; M. Stute, P. Schlosser, B. J. Mailloux, Y. Zheng, I. Choudhury, K.M. Ahmed, A. van Geen
      Abstract: More than 100,000 community wells have been installed in the 150‐300 m depth range throughout Bangladesh over the past decade to provide low‐arsenic drinking water (
      PubDate: 2016-04-12T20:32:34.689413-05:
      DOI: 10.1002/2015WR018224
       
  • Reply to comments by Dingbao Wang on “Climate and agricultural land
           use change impacts on streamflow in the upper Midwestern United
           States”
    • Authors: Satish C. Gupta; Andrew C. Kessler, Melinda K. Brown, William M. Schuh
      PubDate: 2016-04-08T13:03:38.299889-05:
      DOI: 10.1002/2016WR018727
       
  • Statistical analysis of turbulent super‐streamwise vortices based on
           observations of streaky structures near the free surface in the smooth
           open channel flow
    • Authors: Qiang Zhong; Qigang Chen, Hao Wang, Danxun Li, Xingkui Wang
      Abstract: Long streamwise‐elongated high‐ and low‐speed streaks are repeatedly observed near the free surface in open channel flows in natural rivers and lab experiments. Super‐streamwise vortex model has been proposed to explain this widespread phenomenon for quite some time. However, statistical evidence of the existence of the super‐streamwise vortices as one type of coherent structures is still insufficient. Correlation and proper orthogonal decomposition (POD) analysis based on PIV experimental data in the streamwise‐spanwise plane near the free surface in a smooth open channel flow are employed to investigate this topic. Correlation analysis revealed that the streaky structures appear frequently near the free surface and their occurrence probability at any spanwise position is equal. The spanwise velocity fluctuation usually flows from low‐speed streaks toward high‐speed streaks. The average spanwise width and spacing between neighboring low (or high) speed streaks are approximately h and 2h respectively. POD analysis reveals that there are streaks with different spanwise width in the instantaneous flow fields. Typical streamwise rotational movement can be sketched out directly based on the results from statistical analyzes. Point‐by‐point analysis indicates that this pattern is consistent everywhere in the measurement window and is without any inhomogeneity in the spanwise direction, which reveals the essential difference between coherent structures and secondary flow cells. The pattern found by statistical analysis is consistent with the notion that the super‐streamwise vortices exist universally as one type of coherent structure in open channel flows. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-06T14:56:07.46989-05:0
      DOI: 10.1002/2015WR017728
       
  • Daytime sensible heat flux estimation over heterogeneous surfaces using
           multitemporal land‐surface temperature observations
    • Abstract: Equations based on surface renewal (SR) analysis to estimate the sensible heat flux (H) require as input the mean ramp amplitude and period observed in the ramp‐like pattern of the air temperature measured at high frequency. A SR‐based method to estimate sensible heat flux (HSR‐LST) requiring only low‐frequency measurements of the air temperature, horizontal mean wind speed, and land‐surface temperature as input was derived and tested under unstable conditions over a heterogeneous canopy (olive grove). HSR‐LST assumes that the mean ramp amplitude can be inferred from the difference between land‐surface temperature and mean air temperature through a linear relationship and that the ramp frequency is related to a wind shear scale characteristic of the canopy flow. The land‐surface temperature was retrieved by integrating in‐situ sensing measures of thermal infrared energy emitted by the surface. The performance of HSR‐LST was analysed against flux tower measurements collected at two heights (close to and well above the canopy top). Crucial parameters involved in HSR‐LST, which define the above mentioned linear relationship, were explained using the canopy height and the land surface temperature observed at sunrise and sunset. Although the olive grove can behave as either an isothermal or anisothermal surface, HSR‐LST performed close to H measured using the eddy covariance and the Bowen ratio energy balance methods. Root mean square differences between HSR‐LST and measured H were of about 55 W m−2. Thus, by using multi‐temporal thermal acquisitions, HSR‐LST appears to bypass inconsistency between land surface temperature and the mean aerodynamic temperature. The one‐source bulk transfer formulation for estimating H performed reliable after calibration against the eddy covariance method. After calibration, the latter performed similar to the proposed SR‐LST method. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-06T10:36:35.101646-05:
      DOI: 10.1002/2015WR017587
       
  • Contribution of recycled moisture to precipitation in oases of arid
           central Asia: A stable isotope approach
    • Authors: Shengjie Wang; Mingjun Zhang, Yanjun Che, Fenli Chen, Fang Qiang
      Abstract: Terrestrial moisture contributed by surface evaporation and transpiration, also known as recycled moisture, plays an important role in hydrological processes especially across arid central Asia. The stable hydrogen and oxygen isotopes can be used for water budget analysis to calculate the contribution of recycled moisture to precipitation between two locations along the moisture flow. Based on a three‐component isotopic mixing model, the moisture recycling in oasis stations of arid central Asia during summer months is assessed. At large oases of Urumqi, the proportional contribution of recycled moisture to local precipitation is approximately 16.2%, and the mean proportions of surface evaporation and transpiration are 5.9%±1.5% and 10.3%±2.2%, respectively. At small oases like Shihezi and Caijiahu the contribution of recycled moisture is less than 5%, and the proportion of surface evaporation is much less than that of transpiration. The vegetative cover in arid central Asia is generally sparse, but the evapotranspiration contribution to precipitation cannot be ignored at the widely distributed oases. The oasis effect shows great variability depending on locations and water availability for evapotranspiration. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-06T10:36:14.731884-05:
      DOI: 10.1002/2015WR018135
       
  • The psychology of recycled water: Factors predicting disgust and
           willingness to use
    • Abstract: Water recycling is increasingly recognized as a critical strategy to maintain sustainable water supplies. Yet public acceptance of water recycling often lags behind. It is unclear the degree to which individuals are aware of the role of disgust in their decisions about recycled water, how important anticipated disgust is to willingness to use when controlling for other factors, and what the most effective method of presenting information about water recycling would be to decrease disgust reactions and increase willingness to use. We used a two‐pronged approach, combining a survey with open‐ended and psychometric measures with an experimental manipulation, in a US, web‐based sample [N = 428]. Only 2% of participants self‐identified disgust as important to their decisions about recycled water. When measured directly using a Likert scale, however, anticipated disgust was the strongest predictor of willingness to use recycled water when controlling for individual differences that have been shown to impact willingness to use, including a subscale of individual pathogen disgust sensitivity. Finally, participants were exposed to an educational brochure about water reuse framed either affectively or cognitively or were shown a simple, neutral definition. Exposure to either the affectively or cognitively framed brochures lowered anticipated disgust, but did not significantly affect willingness to use recycled water compared to the neutral brochure. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-04T03:45:27.58243-05:0
      DOI: 10.1002/2015WR018340
       
  • Stage‐discharge rating curves based on satellite altimetry and
           modeled discharge in the Amazon Basin
    • Abstract: In this study, rating curves (RCs) were determined by applying satellite altimetry to a poorly gauged basin. This study demonstrates the synergistic application of remote sensing and watershed modeling to capture the dynamics and quantity of flow in the Amazon River Basin, respectively. Three major advancements for estimating basin‐scale patterns in river discharge are described. The first advancement is the preservation of the hydrological meanings of the parameters expressed by Manning's equation to obtain a dataset containing the elevations of the river beds throughout the basin. The second advancement is the provision of parameter uncertainties and, therefore, the uncertainties in the rated discharge. The third advancement concerns estimating the discharge while considering backwater effects. We analyzed the Amazon Basin using nearly one thousand series that were obtained from ENVISAT and Jason‐2 altimetry for more than 100 tributaries. Discharge values and related uncertainties were obtained from the rain‐discharge MGB‐IPH model. We used a global optimization algorithm based on the Monte Carlo Markov Chain and Bayesian framework to determine the rating curves. The data was randomly allocated into 80% calibration and 20% validation subsets. A comparison with the validation samples produced a Nash‐Sutcliffe efficiency (Ens) of 0.68. When the MGB discharge uncertainties were less than 5%, the Ens value increased to 0.81 (mean). A comparison with the in situ discharge resulted in an Ens value of 0.71 for the validation samples (and 0.77 for calibration). The Ens values at the mouths of the rivers that experienced backwater effects significantly improved when the mean monthly slope was included in the RC. Our RCs were not mission dependent, and the Ens value was preserved when applying ENVISAT rating curves to Jason‐2 altimetry at cross‐overs. The cease‐to‐flow parameter of our RCs provided a good proxy for determining river bed elevation. This proxy was validated against Acoustic Doppler current profiler (ADCP) cross sections with an accuracy of more than 90%. Altimetry measurements are routinely delivered within a few days, and this RC dataset provides a simple and cost‐effective tool for predicting discharge throughout the basin in nearly real time. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-04T03:45:01.057146-05:
      DOI: 10.1002/2014WR016618
       
  • Alternating irrigation water quality as a method to control solute
           concentrations and mass fluxes below irrigated fields: A numerical study
    • Authors: David Russo
      Abstract: The aim of the present numerical study was to extend the data‐driven protocol for the control of soil salinity [Russo et al., 2015], to control chloride and nitrate concentrations and mass fluxes below agricultural fields irrigated with treated waste water (TWW). The protocol is based on alternating irrigation water quality between TWW and desalinized water (DSW), guided by solute concentrations at soil depth, zs. Two different schemes, the first requires measurements of soil solution concentrations of chloride and nitrate at zs, while, the second scheme requires only measurements of soil solution EC at zs, were investigated. For this purpose, 3‐D numerical simulations of flow and transport were performed for variably saturated, spatially heterogeneous, flow domains located at two different field sites. The sites differ in crop type, irrigation method and in their lithology; these differences, in turn, considerably affect the performance of the proposed schemes, expressed in terms of their ability to reduce solute concentrations that drained below the root zone. Results of the analyses suggest that the proposed data‐driven schemes allow the use of low‐quality water for irrigation, while minimizing the consumption of high‐quality water to a level, which, for given climate, soil, crop, irrigation method, and water quality, may be determined by the allowable nitrate and chloride concentrations in the groundwater. The results of the present study indicate that with respect to the diminution of groundwater contamination by chloride and nitrate, the more data demanding, first scheme is superior the second scheme. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-04T03:41:42.220744-05:
      DOI: 10.1002/2015WR018287
       
  • Regime‐shifting streamflow processes: Implications for water supply
           reservoir operations
    • Authors: S.W.D. Turner; S. Galelli
      Abstract: This paper examines the extent to which regime‐like behavior in streamflow time series impacts reservoir operating policy performance. We begin by incorporating a regime state variable into a well‐established stochastic dynamic programming model. We then simulate and compare optimized release policies—with and without the regime state variable—to understand how regime shifts affect operating performance in terms of meeting water delivery targets. Our optimization approach uses a hidden Markov model to partition the streamflow time series into a small number of separate regime states. The streamflow persistence structures associated with each state define separate month‐to‐month streamflow transition probability matrices for computing penalty cost expectations within the optimization procedure. The algorithm generates a four‐dimensional array of release decisions conditioned on the within‐year time period, reservoir storage state, inflow class, and underlying regime state. Our computational experiment is executed on 99 distinct, hypothetical water supply reservoirs fashioned from the Australian Bureau of Meteorology's Hydrologic Reference Stations. Results show that regime‐like behavior is a major cause of sub‐optimal operations in water supply reservoirs; conventional techniques for optimal policy design may misguide the operator, particularly in regions susceptible to multi‐year drought. Stationary streamflow models that allow for regime‐like behavior can be incorporated into traditional stochastic optimization models to enhance the flexibility of operations. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-04T03:41:07.685506-05:
      DOI: 10.1002/2015WR017913
       
  • The impact of information on behavior under an ambient‐based policy
           for regulating nonpoint source pollution
    • Authors: Haoran Miao; Jacob Fooks, Todd Guilfoos, Kent Messer, Soni M. Pradhanang, Jordan Suter, Simona Trandafir, Emi Uchida
      Abstract: Stemming from Segerson [1988], literature on nonpoint source pollution shows that ambient‐based regulatory policies can induce polluters in a common watershed to comply with an exogenously determined pollution standard. This study uses laboratory economic experiments in a spatially heterogeneous setting to test the effectiveness of an ambient tax/subsidy policy in a setting with realistic in‐stream nutrient transport dynamics when varying levels of sensor information on ambient pollution is available to the agents and the regulator. We find that increasing the frequency of ambient monitoring improves the spatial allocation of emissions reductions. In particular with more frequent monitoring, the ambient‐based policy induces firms further from the monitoring point to reduce emissions significantly more than downstream firms. Overall, the results suggest that enhanced temporal resolution leads to efficiency gains. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-04T03:39:13.934145-05:
      DOI: 10.1002/2015WR018142
       
  • Understanding satellite‐based monthly‐to‐seasonal
           reservoir outflow estimation as a function of hydrologic controls
    • Authors: Matthew Bonnema; Safat Sikder, Yabin Miao, Xiaodong Chen, Faisal Hossain, Ismat Ara Pervin, S M. Mahbubur Rahman, Hyongki Lee
      Abstract: Growing population and increased demand for water is causing an increase in dam and reservoir construction in developing nations. When rivers cross international boundaries, the downstream stakeholders often have little knowledge of upstream reservoir operation practices. Satellite remote sensing in the form of radar altimetry and multi‐sensor precipitation products can be used as a practical way to provide downstream stakeholders with the fundamentally elusive upstream information on reservoir outflow needed to make important and proactive water management decisions. This study uses a mass balance approach of three hydrologic controls to estimate reservoir outflow from satellite data at monthly and annual time scales: precipitation induced inflow, evaporation, and reservoir storage change. Furthermore, this study explores the importance of each of these hydrologic controls to the accuracy of outflow estimation. The hydrologic controls found to be unimportant could potentially be neglected from similar future studies. Two reservoirs were examined in contrasting regions of the world, the Hungry Horse Reservoir in a mountainous region in northwest U.S. and the Kaptai Reservoir in a low‐lying, forested region of Bangladesh. It was found that this mass balance method estimated the annual outflow of both reservoirs with reasonable skill. The estimation of monthly outflow from both reservoirs was however less accurate. The Kaptai basin exhibited a shift in basin behavior resulting in variable accuracy across the 9‐year study period. Monthly outflow estimation from Hungry Horse Reservoir was compounded by snow accumulation and melt processes, reflected by relatively low accuracy in summer and fall, when snow processes control runoff. Furthermore, it was found that the important hydrologic controls for reservoir outflow estimation at the monthly time scale differs between the two reservoirs, with precipitation induced inflow being the most important control for the Kaptai Reservoir and storage change being the most important for Hungry Horse Reservoir. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-04T03:38:19.808037-05:
      DOI: 10.1002/2015WR017830
       
  • Integrating cobenefits produced with water quality BMPs into credits
           markets: Conceptualization and experimental illustration for EPRI's Ohio
           River Basin trading
    • Authors: Pengfei Liu; Stephen K. Swallow
      Abstract: This paper develops a method that incorporates the public value for environmental co‐benefits when a conservation buyer can purchase water quality credits based on non‐market valuation results. We demonstrate this approach through an experiment with adult students in a classroom laboratory environment. Our application contributes to the study of individual preference and willingness to pay for co‐benefits associated with the production of water quality credits in relation to the Ohio River Basin Trading Project. We use three different methods to elicit individuals' willingness to pay (WTP), including 1) a hypothetical referendum, 2) a real referendum lacking incentive compatibility and 3) a real choice with incentive compatibility. Methodologically, our WTP estimates suggest individuals are more sensitive to the cost changes and reveal the lowest value in the real choice with incentive compatibility. Practically, we find individuals value certain co‐benefits and credits as public goods. Incorporating public value toward co‐benefits may improve the overall efficiency of a water quality trading market. Based on our specification of a planner's welfare function, results suggest a 34% welfare improvement after identifying an optimal allocation of a buyer's budget across credits derived from agricultural management practices producing different portfolios of co‐benefits. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-04T03:37:30.338511-05:
      DOI: 10.1002/2015WR018130
       
  • Impact of Homeowner Association (HOA) landscaping guidelines on
           residential water use
    • Authors: Elizabeth A. Wentz; Sandra Rode, Xiaoxiao Li, Elizabeth M. Tellman, B.L. Turner
      Abstract: The association between increasing water intensive land‐cover, such as the use of turf grass and trees, and increasing water use is a growing concern for water‐stressed arid cities. Appropriate regulatory measures addressing residential landscaping, such as those applied by Homeowner Associations (HOAs), may serve to reduce municipal water use, joining other water‐use reducing measures under consideration by arid cities. This research assesses quantitatively the role that Covenants, Conditions, and Restrictions (CCRs) applied to landscaping by HOAs play on water consumption. Statistical comparisons and models of n=1,973 parcels in Goodyear, Arizona, USA, reveal that: HOA yards have less vegetation cover and those households use less peak‐season water (July) than those households in non‐HOA neighborhoods. This hold true even though the HOA CCRs regulate only the minimum required front‐yard vegetation and most residents maintain more than the minimum vegetation level. Furthermore, front‐yard landscaping tends to be mimicked in the backyard such that total yard landscaping tracks best with total household water use. Results of the study suggest that HOA landscaping regulations have the potential to reduce peak‐season water use by up to 24% if CCRs were to set maximum vegetation regulations rather than minimum and if compliance were enforced. Lowering residential water consumption in this way potentially involves tradeoffs with the cooling effects of vegetation and its consequences on the urban heat island effect, on energy use, and on home values. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-04T03:35:45.502481-05:
      DOI: 10.1002/2015WR018238
       
  • Stream solute tracer time scales changing with discharge and reach length
           confound process interpretation
    • Authors: Noah M. Schmadel; Adam S. Ward, Marie J. Kurz, Jan H. Fleckenstein, Jay P. Zarnetske, David M. Hannah, Theresa Blume, Michael Vieweg, Phillip J. Blaen, Christian Schmidt, Julia L.A. Knapp, Megan J. Klaar, Paul Romeijn, Thibault Datry, Toralf Keller, Silvia Folegot, Amaia I. Marruedo Arricibita, Stefan Krause
      Abstract: Improved understanding of stream solute transport requires meaningful comparison of processes across a wide range of discharge conditions and spatial scales. At reach scales where solute tracer tests are commonly used to assess transport behavior, such comparison is still confounded due to the challenge of separating dispersive and transient storage processes from the influence of the advective timescale that varies with discharge and reach length. To better resolve interpretation of these processes from field‐based tracer observations, we conducted recurrent conservative solute tracer tests along a 1‐km study reach during a storm discharge period and further discretized the study reach into six segments of similar length but different channel morphologies. The resulting suite of data, spanning an order of magnitude in advective timescales, enabled us to (1) characterize relationships between tracer response and discharge in individual segments and (2) determine how combining the segments into longer reaches influences interpretation of dispersion and transient storage from tracer tests. We found that the advective timescale was the primary control on the shape of the observed tracer response. Most segments responded similarly to discharge, implying that the influence of morphologic heterogeneity was muted relative to advection. Comparison of tracer data across combined segments demonstrated that increased advective timescales could be misinterpreted as a change in dispersion or transient storage. Taken together, our results stress the importance of characterizing the influence of changing advective timescales on solute tracer responses before such reach scale observations can be used to infer solute transport at larger network scales. This article is protected by copyright. All rights reserved.
      PubDate: 2016-04-04T03:35:02.491258-05:
      DOI: 10.1002/2015WR018062
       
  • Association of dissolved mercury with dissolved organic carbon in U.S.
           rivers and streams: The role of watershed soil organic carbon
    • Authors: Olivia M. Stoken; Ami L. Riscassi, Todd M. Scanlon
      Abstract: Streams and rivers are important pathways for the export of atmospherically deposited mercury (Hg) from watersheds. Dissolved Hg (HgD) is strongly associated with dissolved organic carbon (DOC) in stream water, but the ratio of HgD to DOC is highly variable between watersheds. In this study, the HgD:DOC ratios from 19 watersheds were evaluated with respect to Hg wet deposition and watershed soil organic carbon (SOC) content. On a subset of sites where data were available, DOC quality measured by specific ultra violet absorbance at 254 nm, was considered as an additional factor that may influence HgD:DOC . No significant relationship was found between Hg wet deposition and HgD:DOC, but SOC content (g m−2) was able to explain 81% of the variance in the HgD:DOC ratio (ng mg−1) following the form: HgD:DOC=17.8*SOC−0.41. The inclusion of DOC quality as a secondary predictor variable explained only an additional 1% of the variance. A mathematical framework to interpret the observed power‐law relationship between HgD:DOC and SOC suggests Hg supply limitation for adsorption to soils with relatively large carbon pools. With SOC as a primary factor controlling the association of HgD with DOC, SOC datasets may be utilized to predict stream HgD:DOC ratios on a more geographically widespread basis. In watersheds where DOC data is available, estimates of HgD may be readily obtained. Future Hg emissions policies must consider soil‐mediated processes that affect the transport of Hg and DOC from terrestrial watersheds to streams for accurate predictions of water quality impacts. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-31T03:26:11.606156-05:
      DOI: 10.1002/2015WR017849
       
  • The importance of base flow in sustaining surface water flow in the Upper
           Colorado River Basin
    • Authors: Matthew P. Miller; Susan G. Buto, David D. Susong, Christine A. Rumsey
      Abstract: The Colorado River has been identified as the most overallocated river in the world. Considering predicted future imbalances between water supply and demand, and the growing recognition that baseflow (a proxy for groundwater discharge to streams) is critical for sustaining flow in streams and rivers, there is a need to develop methods to better quantify present‐day baseflow across large regions. We adapted and applied the spatially referenced regression on watershed attributes (SPARROW) water quality model to assess the spatial distribution of baseflow, the fraction of streamflow supported by baseflow, and estimates of and potential processes contributing to the amount of baseflow that is lost during in‐stream transport in the Upper Colorado River Basin (UCRB). On average, 56% of the streamflow in the UCRB originated as baseflow, and precipitation was identified as the dominant driver of spatial variability in baseflow at the scale of the UCRB, with the majority of baseflow discharge to streams occurring in upper elevation watersheds. The model estimates an average of 1.8x1010 m3/yr of baseflow in the UCRB; greater than 80% of which is lost during in‐stream transport to the Lower Colorado River Basin via processes including evapotranspiration and water diversion for irrigation. Our results indicate that surface waters in the Colorado River Basin are dependent on baseflow, and that management approaches that consider groundwater and surface water as a joint resource will be needed to effectively manage current and future water resources in the Basin. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-31T03:25:47.668725-05:
      DOI: 10.1002/2015WR017963
       
  • Fully coupled atmospheric‐hydrological modeling at regional and
           long‐term scales: Development, application, and analysis of
           WRF‐HMS
    • Authors: Sven Wagner; Benjamin Fersch, Fei Yuan, Zhongbo Yu, Harald Kunstmann
      Abstract: A closed description of the regional water balance requires hydro‐meteorological modeling systems which represent the atmosphere, land surface and subsurface. We developed such a meso‐scale modeling system, extending the atmospheric model WRF with the distributed hydrological model HMS in a fully coupled way. It includes explicit lateral groundwater and land surface flow parameterization schemes and two‐way groundwater‐unsaturated zone interaction by replacing the free drainage bottom boundary of WRF's Noah‐LSM with a Fixed‐head or Darcy‐flux boundary condition. The system is exemplarily applied for the Poyang Lake basin (160,000 km2) and the period 1979‐1986 using a two‐nest approach covering East Asia (30 km) and the Poyang Lake basin (10 km) driven by ERA Interim. Stand‐alone WRF effectively simulates temperature (bias 0.5°C) and precipitation (bias 21‐26%). Stand‐alone HMS simulations provide reasonable streamflow estimates. A significant impact on the regional water balance was found if groundwater‐unsaturated zone interaction is considered. But the differences between the two groundwater coupling approaches are minor. For the fully‐coupled model system, streamflow results strongly depend on the simulation quality for precipitation. Two‐way interaction results in net upward water fluxes in up to 25% of the basin area after the rainy season. In total, two‐way interaction increases basin averaged recharge amounts. The evaluation with CPC and GLEAM indicates a better performance of the fully coupled simulation. The impact of groundwater coupling on LSM and atmospheric variables differs. Largest differences occur for the variable recharge (26%), whereas for atmospheric variables the basin‐averaged impact is minor (
      PubDate: 2016-03-29T03:15:45.985798-05:
      DOI: 10.1002/2015WR018185
       
  • Terrestrial contribution to the heterogeneity in hydrological changes
           under global warming
    • Authors: Sanjiv Kumar; Francis Zwiers, Paul A. Dirmeyer, David M. Lawrence, Rajesh Shrestha, Arelia Werner
      Abstract: This study investigates a physical basis for heterogeneity in hydrological changes, which suggests a greater detectability in wet than dry regions. Wet regions are those where atmospheric demand is less than precipitation (energy‐limited), and dry regions are those where atmospheric demand is greater than precipitation (water‐limited). Long‐term streamflow trends in western North America and an analysis of Coupled Model Intercomparison Project Phase 5 (CMIP5) climate models at global scales show geographically heterogeneous detectability of hydrological changes. We apply the Budyko framework and state‐of‐the‐art climate model data from CMIP5 to quantify the sensitivity and detectability of terrestrial hydrological changes . The Budyko framework quantifies the partitioning of precipitation into evapotranspiration and runoff components. We find that the terrestrial hydrological sensitivity is three times greater in regions where the hydrological cycle is energy‐limited rather than water‐limited. This additional source (the terrestrial part) contributes to 30‐40% greater detectability in energy‐limited regions. We also quantified the contribution of changes in the catchment efficiency parameter that oppose the effects of increasing evaporative demand in global warming scenarios. Incorporating changes to the catchment efficiency parameter in the Budyko framework reduces dry biases in global runoff change projections by 88% in the 21st century. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-28T18:41:20.232635-05:
      DOI: 10.1002/2016WR018607
       
  • Improvement of the hillslope‐storage Boussinesq model by considering
           lateral flow in the unsaturated zone
    • Authors: Jun Kong; Chengji Shen, Zhaoyang Luo, Guofen Hua, Hongjun Zhao
      Abstract: Unsaturated flow is an important factor that affects groundwater motion. Among various drainage models, the nonlinear Hillslope‐storage Boussinesq (HSB) model has been commonly used to predict water flux along a slope. In this study, we improved this model by considering lateral flow in the unsaturated zone. Using modified van Genuchten functions, we analytically expressed the concept of equivalent propagation thickness in the vadose zone. This analytical expression was then incorporated into the HSB model to reflect two different stages of the drainage process and to simulate the hillslope drainage process more accurately. The model results indicated that lateral flow has significant effects in the unsaturated zone during the hillslope drainage process. Even in sandy aquifers, the amount of water contributed by the unsaturated zone is a key factor that enables a decrease in the water table during the middle and late stages of the process. A comparison between the measured and simulated results based on both convergent‐ and divergent‐type hillslope drainage processes revealed that the thickness of the saturated zone decreases as the unsaturated flow increases. This study emphasizes the necessity of considering unsaturated flow in the HSB model to improve the accuracy of predicting groundwater outflow rates and develop more accurate hydrographs. The concept of equivalent propagation thickness also provides a criterion for assessing the importance of unsaturated lateral flow for future drainage research. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-28T18:40:47.253203-05:
      DOI: 10.1002/2015WR018054
       
  • Aquifer imaging with pressure waves—Evaluation of low‐impact
           characterization through sandbox experiments
    • Authors: YaoQuan Zhou; David Lim, Fausto Cupola, Michael Cardiff
      Abstract: Understanding the detailed spatial variation of hydraulic properties in the subsurface has been the subject of intensive research over the past three decades. A recently developed approach to characterize subsurface properties is hydraulic tomography, in which a series of pumping tests are jointly inverted using a heterogeneous numerical model. Recently, Cardiff et al. (2013) proposed a modified tomography approach named Oscillatory Hydraulic Tomography (OHT), in which periodic pumping signals of different frequencies serve as the aquifer stimulation, and pressure responses are recorded at observation locations for tomographic analysis. Its key advantages over traditional hydraulic tomography are that: (1) there is no net injection or extraction of water, and (2) the impulse (an oscillatory signal of known frequency) is easily extracted from noisy data. However, OHT has only been evaluated through numerical experiments to date. In this work, we evaluate OHT performance by attempting to image known heterogeneities in a synthetic aquifer. An instrumented laboratory sandbox is filled with material of known hydraulic properties, and we measure aquifer responses due to oscillatory pumping stimulations at periods of 2, 5, 10, and 20 s. Pressure oscillation time series are processed through Fourier Transforms and inverted tomographically to obtain estimates of aquifer heterogeneity, using a fast, steady‐periodic groundwater flow model. We show that OHT is able to provide robust estimates of aquifer hydraulic conductivity even in cases where relatively few pumping tests and observation locations are available. The use of multiple stimulation frequencies is also shown to improve imaging results.
      PubDate: 2016-03-24T12:23:32.780707-05:
      DOI: 10.1002/2015WR017751
       
  • Movements of the thermocline lead to high variability in benthic mixing in
           the nearshore of a large lake
    • Authors: Mijanur R. Chowdhury; Mathew G. Wells, Todd Howell
      Abstract: The thermocline of Lake Ontario is in constant motion, and as it washes back and forth along the sloping lakebed there is a striking asymmetry in near‐bed stratification and benthic turbulence between its rise and fall. Detailed field observations of the stratification and water currents from the summers of 2012 and 2013 showed that the thermocline motions had large amplitudes (as high as 15 m) and a dominant period between 16‐17.5 h, corresponding to a near‐inertial internal Poincaré wave. During the falling phase, the warmer down‐slope flow was strongly stratified with near‐bed water temperature gradients of 1 oC m−1. In contrast during the rising phase of colder up‐slope flow, there was an unstable stratification in near‐bed water and large temperature overturns due to the differential advection of stratified waters, i.e. the shear‐driven convective mechanism. Using a Thorpe‐scale analysis of overturns, the inferred turbulent diffusivity during the up‐slope flow was Kz =5x10−4 m2 s−1. In striking contrast during the down‐slope flow, the strong stratification had lower turbulent diffusivities of Kz =10−6 m2 s−1. The near bottom region of Lake Ontario within the thermocline swash‐zone has intense biological activity and the highest concentrations of invasive dreissenid mussels. We discuss the potential biological implications of the striking variability in benthic mixing and near‐bed stratification for nutrient cycling in the Lake Ontario nearshore. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-24T03:31:28.408492-05:
      DOI: 10.1002/2015WR017725
       
  • Free phase gas processes in a northern peatland inferred from autonomous
           field‐scale resistivity imaging
    • Abstract: The mechanisms that control free phase gas (FPG) dynamics within peatlands, and therefore estimates of past, present, and future gas fluxes to the atmosphere remain unclear. Electrical resistivity imaging (ERI) is capable of autonomously collecting three dimensional data on the cm to tens of meter scale and thus provides a unique opportunity to observe FPG dynamics in situ. We collected 127 3D ERI datasets as well as water level, soil temperature, atmospheric pressure, and limited methane flux data at a site in a northern peatland over the period July‐August, 2013 to improve the understanding of mechanisms controlling gas releases at a hitherto uncaptured field scale. Our results show the ability of ERI to image the spatial distribution of gas accumulation and infer dynamics of gas migration through the peat column at high (i.e. hourly) temporal resolution. Furthermore, the method provides insights into the role of certain mechanisms previously associated with the triggering of FPG releases such as drops in atmospheric pressure. During these events, buoyancy‐driven gas release primarily occurs in shallow peat as proposed by the ‘shallow peat model.' Releases from the deeper peat are impeded by confining layers, and we observed a large loss of FPG in deep peat that may likely represent a rupture event where accumulated FPG escaped the confining layer as suggested by the 'deep peat model'. Negative linear correlations between water table elevation and resistivity result from hydrostatic pressure regulating bubble volume, although these variations did not appear to trigger FPG transfer or release. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-23T17:51:12.534212-05:
      DOI: 10.1002/2015WR018111
       
  • The role of US states in facilitating effective water governance under
           stress and change
    • Authors: Christine J. Kirchhoff; Lisa Dilling
      Abstract: Worldwide water governance failures undermine effective water management under uncertainty and change. Overcoming these failures requires employing more adaptive, resilient water management approaches; yet, while scholars have advance theory of what adaptive, resilient approaches should be, there is little empirical evidence to support those normative propositions. To fill this gap, we reviewed the literature to derive theorized characteristics of adaptive, resilient water governance including knowledge generation and use, participation, clear rules for water use, and incorporating non‐stationarity. Then, using interviews and documentary analysis focused on five US states' allocation and planning approaches, we examined empirically if embodying these characteristics made states more (or less) adaptive and resilient in practice. We found that adaptive, resilient water governance requires not just possessing these characteristics but combining and building on them. That is, adaptive, resilient water governance requires well‐funded, transparent knowledge systems combined with broad, multi‐level participatory processes that support learning, strong institutional arrangements that establish authorities and rules and that allow flexibility as conditions change, and resources for integrated planning and allocation. We also found that difficulty incorporating climate change or altering existing water governance paradigms and inadequate funding of water programs undermine adaptive, resilient governance. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-23T17:45:44.187274-05:
      DOI: 10.1002/2015WR018431
       
  • Hydrologic modeling in dynamic catchments: A data assimilation approach
    • Authors: S. Pathiraja; L. Marshall, A. Sharma, H. Moradkhani
      Abstract: The transferability of conceptual hydrologic models in time is often limited by both their structural deficiencies and adopted parameterisations. Adopting a stationary set of model parameters ignores biases introduced by the data used to derive them, as well as any future changes to catchment conditions. Although time invariance of model parameters is one of the hallmarks of a high quality hydrologic model, very few (if any) models can achieve this due to their inherent limitations. It is therefore proposed to consider parameters as potentially time varying quantities, which can evolve according to signals in hydrologic observations. In this paper, we investigate the potential for Data Assimilation (DA) to detect known temporal patterns in model parameters from streamflow observations. It is shown that the success of the DA algorithm is strongly dependent on the method used to generate background (or prior) parameter ensembles (also referred to as the parameter evolution model). A range of traditional parameter evolution techniques are considered and found to be problematic when multiple parameters with complex time variations are estimated simultaneously. Two alternative methods are proposed, the first is a Multi‐Layer approach that uses the EnKF to estimate hyperparameters of the temporal structure, based on apriori knowledge of the form of non‐stationarity. The second is a Locally Linear approach that uses local linear estimation and requires no assumptions of the form of parameter non‐stationarity. Both are shown to provide superior results in a range of synthetic case studies, when compared to traditional parameter evolution techniques. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-21T10:39:13.026986-05:
      DOI: 10.1002/2015WR017192
       
  • Using earth‐tide‐induced water pressure changes to measure in
           situ permeability: A comparison with long‐term pumping tests
    • Abstract: Good constraints on hydrogeological properties are an important first step in any quantitative model of groundwater flow. Field estimation of permeability is difficult as it varies over orders of magnitude in natural systems and is scale‐dependent. Here we directly compare permeabilities inferred from tidal responses with conventional large‐scale, long‐term pumping tests at the same site. Tidally induced water pressure changes recorded in wells are used to infer permeability at ten locations in a densely fractured sandstone unit. Each location is either an open‐hole well or a port in a multilevel monitoring well. Tidal response is compared at each location to the results of two conventional, long‐term and large scale pumping tests performed at the same site. We obtained consistent values between the methods for a range of site‐specific permeabilities varying from ∼10−15 m2 to 10−13 m2 for both open wells with large open intervals and multilevel monitoring well. We conclude that the tidal analysis is able to capture passive and accurate estimates of permeability. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-21T10:38:07.560513-05:
      DOI: 10.1002/2015WR017346
       
  • Numerical experiments to explain multiscale hydrological responses to
           mountain pine beetle tree mortality in a headwater watershed
    • Authors: Colin A. Penn; Lindsay A. Bearup, Reed M. Maxwell, David W. Clow
      Abstract: The effects of mountain pine beetle (MPB)‐induced tree mortality on a headwater hydrologic system were investigated using an integrated physical modeling framework with a high‐resolution computational grid. Simulations of MPB‐affected and unaffected conditions, each with identical atmospheric forcing for a normal water year, were compared at multiple scales to evaluate the effects of scale on MPB‐affected hydrologic systems. Individual locations within the larger model were shown to maintain hillslope‐scale processes affecting snowpack dynamics, total evapotranspiration, and soil moisture that are comparable to several field‐based studies and previous modeling work. Hillslope‐scale analyses also highlight the influence of compensating changes in evapotranspiration and snow processes. Reduced transpiration in the Grey Phase of MPB‐induced tree mortality was offset by increased late‐summer evaporation, while overall snowpack dynamics were more dependent on elevation effects than MPB‐induced tree mortality. At the watershed scale, unaffected areas obscured the magnitude of MPB effects. Annual water yield from the watershed increased during Grey Phase simulations by 11 percent; a difference that would be difficult to diagnose with long‐term gage observations that are complicated by inter‐annual climate variability. The effects on hydrology observed and simulated at the hillslope scale can be further damped at the watershed scale, which spans more life zones and a broader range of landscape properties. These scaling effects may change under extreme conditions, e.g. increased total MPB‐affected area or a water year with above average snowpack. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-21T10:29:23.221334-05:
      DOI: 10.1002/2015WR018300
       
  • Recovery times of riparian vegetation
    • Authors: R. Vesipa; C. Camporeale, L. Ridolfi
      Abstract: Riparian vegetation is a key element in a number of processes that determine the eco‐geomorphological features of the river landscape. Depending on the river water stage uctuations, vegetation biomass randomly switches between growth and degradation phases, and exhibits relevant temporal variations. A full understanding of vegetation dynamics is therefore only possible if the hydrological stochastic forcing is considered. In this vein, we focus on the recovery time of vegetation, namely the typical time taken by vegetation to recover a well developed state starting from a low biomass value (induced, for instance, by an intense ood). The analytical expression of the plot‐dependent recovery time is given, the role of hydrological and biological parameters is discussed, and the impact of river‐induced randomness is highlighted. Finally, the effect of man‐induced hydrological changes (e.g., river damming or climate changes) is explored. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-21T10:26:57.252114-05:
      DOI: 10.1002/2015WR018490
       
  • Fluvial geomorphology and aquatic‐to‐terrestrial Hg export are
           weakly coupled in small urban streams of Columbus, Ohio
    • Abstract: Although mercury (Hg) contamination is common in stream ecosystems, mechanisms governing bioavailability and bioaccumulation in fluvial systems remain poorly resolved as compared to lentic systems. In particular, streams in urbanized catchments are subject to fluvial geomorphic alterations that may contribute to Hg distribution, bioaccumulation, and export across the aquatic‐to‐terrestrial boundary. In 12 streams of urban Columbus, Ohio, we investigated the influence of fluvial geomorphic characteristics related to channel geometry, streamflow, and sediment size and distribution on (1) Hg concentrations in sediment and body burdens in benthic larval and adult emergent aquatic insects and (2) aquatic‐to‐terrestrial contaminant transfer to common riparian spiders of the families Pisauridae and Tetragnathidae via changes in aquatic insect Hg body burdens as well as in aquatic insect density and community composition. Hydrogeomorphic characteristics were weakly related to Hg body burdens in emergent insects (channel geometry) and tetragnathid spiders (streamflow), but not to Hg concentrations in sediment or benthic insects. Streamflow characteristics were also related to emergent insect density, while wider channels were associated with benthic insect community shifts towards smaller‐bodied and more tolerant taxa (e.g., Chironomidae). Thus, our results provide initial evidence that fluvial geomorphology may influence aquatic‐to‐terrestrial contaminant Hg transfer through the collective effects on emergent insect body burdens as well as on aquatic insect community composition and abundance. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-18T18:18:14.815478-05:
      DOI: 10.1002/2015WR018416
       
  • Calibration of soil moisture sensing with subsurface heated fiber optics
           using numerical simulation
    • Abstract: The heat pulse probe method can be implemented with actively heated fiber optics (AHFO) to obtain distributed measurements of soil water content (θ) by using reported soil thermal responses measured by Distributed Temperature Sensing (DTS) and with a soil‐specific calibration relationship. However, most reported applications have been calibrated to homogeneous soils in a laboratory, while inexpensive efficient in‐situ calibration procedures useful in heterogeneous soils are lacking. Here we employed the Hydrus 2D/3D code to define a soil‐specific calibration curve. We define a 2D geometry of the fiber optic cable and the surrounding soil media, and simulate heat pulses to capture the soil thermal response at different soil water contents. The model was validated in an irrigated field using DTS data from two locations along the FO deployment in which reference moisture sensors were installed. Results indicate that θ was measured with the model‐based calibration with accuracy better than 0.022 m3 m−3. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-18T18:17:50.03448-05:0
      DOI: 10.1002/2015WR017897
       
  • Simulating bioclogging effects on dynamic riverbed permeability and
           infiltration
    • Authors: Michelle E. Newcomer; Susan S. Hubbard, Jan H. Fleckenstein, Ulrich Maier, Christian Schmidt, Martin Thullner, Craig Ulrich, Nicolas Flipo, Yoram Rubin
      Abstract: Bioclogging in rivers can detrimentally impact aquifer recharge. This is particularly so in dry regions, where losing rivers are common, and where disconnection between surface water and groundwater (leading to the development of an unsaturated zone) can occur. Reduction in riverbed permeability due to biomass growth is a time‐variable parameter that is often neglected, yet permeability reduction from bioclogging can introduce order of magnitude changes in seepage fluxes from rivers over short (i.e., monthly) timescales. To address the combined effects of bioclogging and disconnection on infiltration, we developed numerical representations of bioclogging processes within a one‐dimensional, variably‐saturated flow model representing losing‐connected and losing‐disconnected rivers. We tested these formulations using a synthetic case study informed with biological data obtained from the Russian River, California, U.S.A. Our findings show that modeled biomass growth reduced seepage for losing‐connected and losing‐disconnected rivers. However, for rivers undergoing disconnection, infiltration declines occurred only after the system was fully disconnected. Before full disconnection, biologically‐induced permeability declines were not significant enough to offset the infiltration gains introduced by disconnection. The two effects combine to lead to a characteristic infiltration curve where peak infiltration magnitude and timing is controlled by permeability declines relative to hydraulic gradient gains. Biomass growth was found to hasten the onset of full disconnection; a condition we term ‘effective disconnection'. Our results show that river infiltration can respond dynamically to bioclogging and subsequent permeability declines that are highly dependent on river connection status. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-18T18:17:26.177866-05:
      DOI: 10.1002/2015WR018351
       
  • A laboratory study to estimate pore geometric parameters of sandstones
           using complex conductivity and nuclear magnetic resonance for permeability
           prediction
    • Authors: Gordon Osterman; Kristina Keating, Andrew Binley, Lee Slater
      Abstract: We estimate parameters from the Katz and Thompson permeability model using laboratory complex electrical conductivity (CC) and nuclear magnetic resonance (NMR) data to build permeability models parameterized with geophysical measurements. We use the Katz and Thompson model based on the characteristic hydraulic length scale, determined from mercury injection capillary pressure estimates of pore throat size, and the intrinsic formation factor, determined from multi‐salinity conductivity measurements, for this purpose. Two new permeability models are tested, one based on CC data and another that incorporates CC and NMR data. From measurements made on forty‐five sandstone cores collected from fifteen different formations, we evaluate how well the CC relaxation time and the NMR transverse relaxation times compare to the characteristic hydraulic length scale and how well the formation factor estimated from CC parameters compares to the intrinsic formation factor. We find: (1) the NMR transverse relaxation time models the characteristic hydraulic length scale more accurately than the CC relaxation time (R2 of 0.69 and 0.39 and normalized root mean square errors (NRMSE) of 0.16 and 0.20, respectively); (2) the CC estimated formation factor is well correlated with the intrinsic formation factor (NRMSE=0.23). We demonstrate that that permeability estimates from the joint‐NMR‐CC model (NRMSE=0.13) compare favorably to estimates from the Katz and Thompson model (NRMSE=0.074). This model advances the capability of the Katz and Thompson model by employing parameters measureable in the field giving it the potential to more accurately estimate permeability using geophysical measurements than are currently possible. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-18T18:16:59.799346-05:
      DOI: 10.1002/2015WR018472
       
  • Combining information from multiple flood projections in a hierarchical
           Bayesian framework
    • Authors: Nataliya Le Vine
      Abstract: This study demonstrates, in the context of flood frequency analysis, the potential of a recently proposed hierarchical Bayesian approach to combine information from multiple models. The approach explicitly accommodates shared multi‐model discrepancy as well as the probabilistic nature of the flood estimates, and treats the available models as a sample from a hypothetical complete (but unobserved) set of models. The methodology is applied to flood estimates from multiple hydrological projections (the Future Flows Hydrology dataset) for 135 catchments in the UK. The advantages of the approach are shown to be: 1) to ensure adequate ‘baseline' with which to compare future changes; 2) to reduce flood estimate uncertainty; 3) to maximise use of statistical information in circumstances where multiple weak predictions individually lack power, but collectively provide meaningful information; 4) to diminish the importance of model consistency when model biases are large; and 5) to explicitly consider the influence of the (model performance) stationarity assumption. Moreover, the analysis indicates that reducing shared model discrepancy is the key to further reduction of uncertainty in the flood frequency analysis. The findings are of value regarding how conclusions about changing exposure to flooding are drawn, and to flood frequency change attribution studies. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-18T18:16:34.210896-05:
      DOI: 10.1002/2015WR018143
       
  • Joint editorial—Fostering innovation and improving impact assessment
           for journal publications in hydrology
    • Abstract: Editors of several journals in the field of hydrology met during the Assembly of the International Association of Hydrological Sciences—IAHS (within the Assembly of the International Union of Geodesy and Geophysics—IUGG) in Prague in June 2015. This event was a follow‐up of a similar meeting held in July 2013 in Gothenburg (as reported by Blöschl et al., 2014). These meetings enable the group of editors to review the current status of the journals and the publication process, and share thoughts on future strategies. Journals were represented in the 2015 meeting through their editors, as shown in the list of authors. The main points on fostering innovation and improving impact assessment in journal publications in hydrology are communicated in this joint editorial published in the above journals. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-18T18:16:09.325791-05:
      DOI: 10.1002/2016WR018895
       
  • Effect of tillage on macropore flow and phosphorus transport to tile
           drains
    • Authors: Mark R. Williams; Kevin W. King, William Ford, Anthony R. Buda, Casey D. Kennedy
      Abstract: Elevated phosphorus (P) concentrations in subsurface drainage water are thought to be the result of P bypassing the soil matrix via macropore flow. The objectives of this study were to quantify event water delivery to tile drains via macropore flow paths during storm events and to determine the effect of tillage practices on event water and P delivery to tiles. Tile discharge, total dissolved P (DP) and total P (TP) concentrations, and stable oxygen and deuterium isotopic signatures were measured from two adjacent tile‐drained fields in Ohio, USA during seven spring storms. Fertilizer was surface‐applied to both fields and disk tillage was used to incorporate the fertilizer on one field while the other remained in no‐till. Median DP concentration in tile discharge prior to fertilizer application was 0.08 mg L−1 in both fields. Following fertilizer application, median DP concentration was significantly greater in the no‐tilled field (1.19 mg L−1) compared to the tilled field (0.66 mg L−1), with concentrations remaining significantly greater in the no‐till field for the remainder of the monitored storms. Both DP and TP concentrations in the no‐till field were significantly related to event water contributions to tile discharge, while only TP concentration was significantly related to event water in the tilled field. Event water accounted for between 26‐69% of total tile discharge from both fields, but tillage substantially reduced maximum contributions of event water. Collectively, these results suggest that incorporating surface‐applied fertilizers has the potential to substantially reduce the risk of P transport from tile‐drained fields. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-18T18:15:45.443285-05:
      DOI: 10.1002/2015WR017650
       
  • Robust flood frequency analysis: Performance of EMA with multiple
           Grubbs‐Beck outlier tests
    • Authors: J.R. Lamontagne; J.R. Stedinger, Xin Yu, C.A. Whealton, Ziyao Xu
      Abstract: Flood frequency analysis generally involves the use of simple parametric probability distributions to smooth and extrapolate the information provided by short flood records to estimate extreme flood flow quantiles. Parametric probability distributions can have difficulty simultaneously fitting both the largest and smallest floods. A danger is that the smallest observations in a record can distort the exceedance probabilities assigned to the large floods of interest. The identification and treatment of such Potentially Influential Low Floods (PILFs) frees a fitting algorithm to describe the distribution of the larger observations. This can allow parametric flood frequency analysis to be both efficient, and also robust to deviations from the proposed probability model's lower tail. Historically, PILF identification involved subjective judgement. We propose a new multiple Grubbs‐Beck outlier test (MGBT) for objective PILF identification. MGBT PILF identification rates (akin to Type I errors) are reported for the log‐Normal (LN) distribution, and the log‐Pearson Type III (LP3) distribution with a variety of skew coefficients. MGBT PILF identification generally matched subjective identification from a recent California flood frequency study. Monte Carlo results show that censoring of PILFs identified by the MGBT algorithm improves the extreme quantile estimator efficiency of the expected moments algorithm (EMA) for negatively skewed LP3 distributions and has little effect for zero or positive skews; simultaneously it protects against deviations from the LP3 in the lower tail, as illustrated by distorted LN examples. Thus, MGBT generally makes flood frequency analysis based on the LP3 distribution with EMA both more accurate and more robust. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-18T18:15:18.568633-05:
      DOI: 10.1002/2015WR018093
       
  • Thermal convection of temperature‐dependent viscous fluids within
           three‐dimensional faulted geothermal systems: Estimation from linear
           and numerical analyses
    • Authors: Victor .I. Malkovsky; Fabien Magri
      Abstract: Linear stability analysis and numerical simulations of density‐driven flow are presented in order to estimate the effects of temperature‐dependent fluid viscosity variation on the onset of free thermal convection within a three‐dimensional fault embedded into impermeable rocks. The strongly‐coupled equations of density‐driven flow are linearized. The solution was obtained through expansion into Fourier series. Simple polynomial expressions fitting the neutral stability curves are given for a range of fault aspect ratios, fluid viscosity properties and thermal conductivity heterogeneity, providing a new tool for the estimation of critical Rayleigh numbers in faulted systems. The results are validated against the limiting case of temperature‐invariant viscosity (i.e. constant). 3D numerical simulations of free convection within a fault are run using the finite element technique in order to verify the theoretical results. It turned out that at average geothermal temperature conditions, thermal convection can develop within faults which permeability is up to four times lower than the case of a fluid with constant viscosity, in agreement with the developed linear theory. The polynomial expressions of this study can be applied to any numerical model for testing the feasibility of fault‐convection in 3D geothermal basin. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-18T18:14:50.150027-05:
      DOI: 10.1002/2015WR018001
       
  • On the use of SRTM and altimetry data for flood modeling in data sparse
           regions
    • Authors: Alessio Domeneghetti
      Abstract: The growing availability of remotely sensed data has fostered the implementation of hydraulic modeling in poorly gauged regions. However, these applications suffer the lack of knowledge of river bathymetry, which cannot be directly inferred from satellite instruments. This study explores the possibility to set‐up, calibrate and validate a hydrodynamic model which geometry is based on global and freely available satellite data. First, the study tests two different procedures for inferring the river bathymetry under the water surface level. Second, focusing on a Po River stretch of ∼ 140 km (Northern Italy), the study further assesses the suitability of space‐borne topographic and remotely sensed altimetry data (i.e. ERS‐2 and ENVISAT) for implementing and calibrating hydrodynamic models. Referring to 90 m SRTM (Shuttle Radar Topography Mission) digital elevation model for the representation of the riverbed morphology, the work analyzes the performances of different 1D numerical models which cross‐sections are modified according to two approaches: (1) Channel Bankfull depth (CB) and (2) Slope‐Break (SB) approach. The calibration and validation processes are performed by referring to extended altimetry time series (∼ 16 years of data), while the accuracy and trustworthiness of 1D models are tested with reference to a quasi‐2D model based on detailed geometry data. Results show that both CB and SB approaches enhance the performance of SRTM‐based models. In particular, the SB approach is completely based on satellite‐borne data and shows Nash‐Sutcliffe efficiency, MAE and RMSE values similar to those obtained with the benchmark model. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-18T18:13:41.06893-05:0
      DOI: 10.1002/2015WR017967
       
  • Toward improved prediction of the bedrock depth underneath hillslopes:
           Bayesian inference of the bottom‐up control hypothesis using
           high‐resolution topographic data
    • Abstract: The depth to bedrock controls a myriad of processes by influencing subsurface flow paths, erosion rates, soil moisture and water uptake by plant roots. As hillslope interiors are very difficult and costly to illuminate and access, the topography of the bedrock surface is largely unknown. This essay is concerned with the prediction of spatial patterns in the depth to bedrock (DTB) using high‐resolution topographic data, numerical modeling and Bayesian analysis. Our DTB model builds on the bottom‐up control on fresh‐bedrock topography hypothesis of\cite{Rempe2014} and includes a mass movement and bedrock‐valley morphology term to extent the usefulness and general applicability of the model. We reconcile the DTB model with field observations using Bayesian analysis with the DREAM algorithm\citep{Vrugt2008,Vrugt2009}. We investigate explicitly the benefits of using spatially distributed parameter values to account implicitly, and in a relatively simple way, for rock mass heterogeneities that are very difficult, if not impossible, to characterize adequately in the field. We illustrate our method using an artificial data set of bedrock depth observations and then evaluate our DTB model with real‐world data collected at the Papagaio river basin in Rio de Janeiro, Brazil. Our results demonstrate that the DTB model predicts accurately the observed bedrock depth data. The posterior mean DTB simulation is shown to be in good agreement with the measured data. The posterior prediction uncertainty of the DTB model can be propagated forward through hydromechanical models to derive probabilistic estimates of factors of safety. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-18T18:13:06.488547-05:
      DOI: 10.1002/2015WR018147
       
  • Watershed model calibration to the base flow recession curve with and
           without evapotranspiration effects
    • Authors: S.M. Jepsen; T.C. Harmon, Y. Shi
      Abstract: Calibration of watershed models to the shape of the baseflow recession curve is a way to capture the important relationship between groundwater discharge and subsurface water storage in a catchment. In some montane Mediterranean regions, such as the mid‐elevation Providence Creek catchment in the southern Sierra Nevada of California (USA), nearly all baseflow recession occurs after snowmelt, and during this time evapotranspiration (ET) usually exceeds baseflow. We assess the accuracy to which watershed models can be calibrated to ET‐dominated baseflow recession in Providence Creek, both in terms of fitting a discharge time‐series and realistically capturing the observed discharge‐storage relationship for the catchment. Model parameters estimated from calibrations to ET‐dominated recession are compared to parameters estimated from reference calibrations to baseflow recession with ET‐effects removed (“potential recession”). We employ the Penn State Integrated Hydrologic Model (PIHM) for simulations of baseflow and ET, and methods that are otherwise general in nature. In models calibrated to ET‐dominated recession, simulation errors in ET and the targeted relationship for recession (−dQ/dt versus Q) contribute substantially (up to 57% and 46%, respectively) to overestimates in the discharge‐storage differential, defined as d(lnQ)/dS, relative to that derived from water flux observations. These errors result in overestimates of deep‐subsurface hydraulic conductivity in models calibrated to ET‐dominated recession, by up to an order of magnitude, relative to reference calibrations to potential recession. These results illustrate a potential opportunity for improving model representation of discharge‐storage dynamics by calibrating to the shape of baseflow recession after removing the complicating effects of ET. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-18T18:11:12.396603-05:
      DOI: 10.1002/2015WR017827
       
  • Spatial and temporal variations in nitrogen export from a New Zealand
           pastoral catchment revealed by stream water nitrate isotopic composition
    • Authors: Naomi S. Wells; W. Troy Baisden, Travis Horton, Tim J. Clough
      Abstract: Viable indicators of nitrogen (N) attenuation at the catchment scale are needed in order to sustainably manage global agricultural intensification. We hypothesized that the dominance of a single land use (pasture production) and strong ground‐to‐surface water connectivity would combine to create a system in which surface water nitrate isotopes (δ15N and δ18O of NO3‐) could be used to monitor variations in catchment‐scale attenuation. Nitrate isotopes were measured monthly over a two‐year period in four reaches along a spring‐fed, gaining stream (mean NO3‐‐N of 6 mg l−1) in Canterbury, New Zealand. The streamwater NO3‐ pool indicated that the highest degree of denitrification occurred in the shallow upper reaches. Moving downstream through increasingly sandy soils, the isotopic signature of denitrification became progressively weaker. The lowest reaches fell into the expected range for NO3‐ produced from the nitrification of pasture N sources (urine and fertilizers), implying that the attenuation capacity of the groundwater and riparian systems was lower than the rate of N inputs. After excluding months affected by effluent spills or extreme weather (n = 4), variations in the degree of denitrification over stream distance were combined with the measured NO3‐ discharge to estimate N attenuation over time in the sub‐catchment. Attenuation was highly responsive to rainfall: 93% of calculated attenuation (20 kg NO3‐‐N ha−1 y−1) occurred within 48 h of rainfall. These findings demonstrate the potential for detailed NO3‐ stable isotope data to provide integrative measures of catchment NO3‐ loss pathways. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-18T18:10:45.724131-05:
      DOI: 10.1002/2015WR017642
       
  • Smart pilot points using reversible‐jump Markov‐chain Monte
           Carlo
    • Abstract: Pilot points are typical means for calibration of highly parameterized numerical models. We propose a novel procedure based on estimating not only the pilot point values, but also their number and suitable locations. This is accomplished by a trans‐dimensional Bayesian inversion procedure that also allows for uncertainty quantification. The utilized algorithm, reversible‐jump Markov‐Chain Monte Carlo (RJ‐MCMC), is computationally demanding and this challenges the application for model calibration. We present a solution for fast, approximate simulation through the application of a Bayesian inversion. A fast pathfinding algorithm is used to estimate tracer travel times instead of doing a full transport simulation. This approach extracts the information from measured breakthrough curves, which is crucial for the reconstruction of aquifer heterogeneity. As a result, the “smart pilot points” can be tuned during thousands of rapid model evaluations. This is demonstrated for both a synthetic and a field application. For the selected synthetic layered aquifer, two different hydrofacies are reconstructed. For the field investigation, multiple fluorescent tracers were injected in different well screens in a shallow alluvial aquifer and monitored in a tomographic source‐receiver configuration. With the new inversion procedure, a sand layer was identified and reconstructed with a high spatial resolution in 3‐D. The sand layer was successfully validated through additional slug tests at the site. The promising results encourage further applications in hydrogeological model calibration, especially for cases with simulation of transport. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-18T18:04:29.246-05:00
      DOI: 10.1002/2015WR017922
       
  • Reply to Comment by Sahoo et al. on “Quantifying renewable
           groundwater stress with GRACE”
    • PubDate: 2016-03-18T10:56:24.93924-05:0
      DOI: 10.1002/2015WR018329
       
  • Appreciation of peer reviewers for 2015
    • PubDate: 2016-03-15T11:05:39.708193-05:
      DOI: 10.1002/2016WR018922
       
  • Roughness, Resistance, and Dispersion: Relationships in Small Streams
    • Authors: Christian Noss; Andreas Lorke
      Abstract: Although relationships between roughness, flow, and transport processes in rivers and streams have been investigated for several decades, the prediction of flow resistance and longitudinal dispersion in small streams is still challenging. Major uncertainties in existing approaches for quantifying flow resistance and longitudinal dispersion at the reach scale arise from limitations in the characterization of riverbed roughness. In this study, we characterized the riverbed roughness in small moderate‐gradient streams (0.1‐0.5% bed slope) and investigated its effects on flow resistance and dispersion. We analyzed high‐resolution transect‐based measurements of stream depth and width, which resolved the complete roughness spectrum with scales ranging from the micro to the reach scale. Independently measured flow resistance and dispersion coefficients were mainly affected by roughness at spatial scales between the median grain size and the stream width, i.e. by roughness between the micro‐ and the mesoscale. We also compared our flow resistance measurements with calculations using various flow resistance equations. Flow resistance in our study streams was well approximated by the equations that were developed for high gradient streams (> 1%) and it was overestimated by approaches developed for sand‐bed streams with a smooth riverbed or ripple bed. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-14T10:33:47.686672-05:
      DOI: 10.1002/2015WR017449
       
  • Comment on “Quantifying renewable groundwater stress with
           GRACE” by Alexandra S. Richey et al.
    • Authors: Sasmita Sahoo; Tess Russo, Upmanu Lall
      Abstract: Richey et al. [2015a] estimate groundwater stress for 37 of the world's largest aquifer systems. Their results suggest a positive annual linear trend in groundwater storage in the Ogallala/High Plains Aquifer, USA (herein referred to as High Plains) using NASA's GRACE satellite data, while previous studies and our analysis using groundwater level observations over the same time period show groundwater depletion. This comment is limited to results from the High Plains, but raises questions about how best to interpret GRACE‐derived results for major aquifers globally. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-14T10:28:13.790217-05:
      DOI: 10.1002/2015WR018085
       
  • Tracking multiple sediment cascades at the river network scale identifies
           controls and emerging patterns of sediment connectivity
    • Authors: Rafael J. P. Schmitt; Simone Bizzi, Andrea Castelletti
      Abstract: Sediment connectivity in fluvial networks results from the transfer of sediment between multiple sources and sinks. Connectivity scales differently between all sources and sinks as a function of distance, source grain size and sediment supply, network topology and topography, and hydrologic forcing. In this paper, we address the challenge of quantifying sediment connectivity and its controls at the network scale. We expand the concept of a single, catchment‐scale sediment cascade towards representing sediment transport from each source as a suite of individual cascading processes. We implement this approach in the herein presented CAtchment Sediment ConnectivityAnd DElivery (CASCADE) modeling framework. In CASCADE, each sediment cascade establishes connectivity between a specific source and its multiple sinks. From a source perspective, the fate of sediment is controlled by its detachment and downstream transport capacity, resulting in a specific trajectory of transfer and deposition. From a sink perspective, the assemblage of incoming cascades defines provenance, sorting, and magnitude of sediment deliveries. At the network scale, this information reveals emerging patterns of connectivity and the location of bottlenecks, where dis‐connectivity occurs. In this paper, we apply CASCADE to quantitatively analyze the sediment connectivity of a major river system in SE Asia. The approach provides a screening model that can support analyses of large, poorly monitored river systems. We test the sensitivity of CASCADE to various parameters and identify the distribution of energy between the multiple, simultaneously active sediment cascades as key control behind network sediment connectivity at the network scale. To conclude, CASCADE enables a quantitative, spatially explicit analysis of network connectivity with potential applications in both river science and management. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-12T01:58:59.386833-05:
      DOI: 10.1002/2015WR018097
       
  • Evaluating the relative air permeability of porous media from their water
           retention curves
    • Authors: S. Assouline; A. Tuli, J.W. Hopmans
      Abstract: Accurate modeling of water and air flow in porous media requires the definition of the relevant hydraulic properties, namely, the water retention curve (WRC) and the relative hydraulic conductivity function (RHC), as well as the definition of the relative air permeability function (RAP). Capitalizing on the approach developed previously to represent the RHC (Assouline, 2001), a new model allowing the prediction of RAP based on information resulting from the WRC is proposed. The power value ηa in the model is a decreasing exponential function of the coefficient of variation, ε, characterizing the pore size distribution of the porous medium, and stemming from its WRC. The model was calibrated using data from 22 disturbed and undisturbed soil samples and was validated using data from 6 soil samples ranging from sand to silty clay loam. The proposed model provided accurate prediction of the soil RAP and performed in some cases (sandy loam and silty clay loam soils) better than available alternative models. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-12T01:58:45.089637-05:
      DOI: 10.1002/2015WR018286
       
  • Predicting long‐term streamflow variability in moist eucalypt
           forests using forest growth models and a sapwood area index
    • Authors: D. Jaskierniak; G. Kuczera, R. Benyon
      Abstract: A major challenge in surface hydrology involves predicting streamflow in ungauged catchments with heterogeneous vegetation and spatiotemporally varying evapotranspiration (ET) rates. We present a top‐down approach for quantifying the influence of broad‐scale changes in forest structure on ET and hence streamflow. Across three catchments between 18 and 100 km2 in size and with regenerating Eucalyptus regnans and E. delegatensis forest, we demonstrate how variation in ET can be mapped in space and over time using LiDAR data and commonly available forest inventory data. The model scales plot‐level sapwood area (SA) to the catchment‐level using basal area (BA) and tree stocking density (N) estimates in forest growth models. The SA estimates over a 69 year regeneration period are used in a relationship between SA and vegetation induced streamflow loss (L) to predict annual streamflow (Q) with annual rainfall (P) estimates. Without calibrating P, BA, N, SA, and L to Q data, we predict annual Q with R2 between 0.68 and 0.75 and Nash Sutcliffe efficiency (NSE) between 0.44 and 0.48. To remove bias, the model was extended to allow for runoff carry‐over into the following year as well as minor correction to rainfall bias, which produced R2 values between 0.72 and 0.79, and NSE between 0.70 and 0.79. The model under‐predicts streamflow during drought periods as it lacks representation of ecohydrological processes that reduce L with either reduced growth rates or rainfall interception during drought. Refining the relationship between sapwood thickness and forest inventory variables is likely to further improve results. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-09T17:44:05.78706-05:0
      DOI: 10.1002/2015WR018029
       
  • Exploring the influence of precipitation extremes and human water use on
           total water storage (TWS) changes in the
           Ganges‐Brahmaputra‐Meghna River Basin
    • Abstract: Climate extremes such as droughts and intense rainfall events are expected to strongly influence global/regional water resources in addition to the growing demands for freshwater. This study examines the impacts of precipitation extremes and human water usage on total water storage (TWS) over the Ganges‐Brahmaputra‐Meghna (GBM) River Basin in South Asia. Monthly TWS changes derived from GRACE (2002‐2014) and soil moisture from three reanalyses (1979‐2014) are used to estimate new extreme indices. These indices are applied in conjunction with standardised precipitation indices (SPI) to explore the impacts of precipitation extremes on TWS in the region. The results indicate that although long‐term precipitation do not indicate any significant trends over the two sub‐basins (Ganges and Brahmaputra‐Meghna), there is significant decline in rainfall (9.0±4.0 mm/decade) over the Brahmaputra‐Meghna River Basin from 1998‐2014. Both river basins exhibit a rapid decline of TWS from 2002‐2014 (Ganges: 12.2±3.4 km3/year and Brahmaputra‐Meghna: 9.1±2.7 km3/year). While the Ganges River Basin has been regaining TWS (5.4±2.2 km3/year) from 2010 onwards, the Brahmaputra‐Meghna River Basin showed a further decline (13.0±3.2 km3/year) in TWS from 2011 onwards. The impact of human water consumption on TWS appears to be considerably higher in Ganges compared to Brahmaputra‐Meghna, where it is mainly concentrated over Bangladesh. The interannual water storage dynamics are found to be strongly associated with meteorological forcing data such as precipitation. In particular, extreme drought conditions, such as those of 2006 and 2009, had profound negative impacts on the TWS, where groundwater resources are already being unsustainably exploited. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-04T13:54:36.271696-05:
      DOI: 10.1002/2015WR018113
       
  • Time varying nonstationary multivariate risk analysis using a dynamic
           Bayesian copula
    • Abstract: A time varying risk analysis is proposed for an adaptive design framework in non‐stationary conditions arising from climate change. A Bayesian, dynamic conditional copula is developed for modeling the time‐varying dependence structure between mixed continuous and discrete multi‐attributes of multi‐dimensional hydro‐meteorological phenomena. Joint Bayesian inference is carried out to fit the marginals and copula in an illustrative example using an adaptive, Gibbs Markov Chain Monte Carlo (MCMC) sampler. Posterior mean estimates and credible intervals are provided for the model parameters and the Deviance Information Criterion (DIC) is used to select the model that best captures different forms of non‐stationarity over time. This study also introduces a fully Bayesian, time‐varying joint return period for multivariate time‐dependent risk analysis in non‐stationary environments. The results demonstrate that the nature and the risk of extreme‐climate multi‐dimensional processes are changed over time under the impact of climate change, and accordingly the long‐term decision making strategies should be updated based on the anomalies of the non‐stationary environment. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-04T12:03:48.952296-05:
      DOI: 10.1002/2015WR018525
       
  • Closed‐flow column experiments—Insights into solute transport
           provided by a damped oscillating breakthrough behavior
    • Authors: Thomas Ritschel; Kai Uwe Totsche
      Abstract: Transport studies that employ column experiments in closed‐flow mode complement classical approaches by providing new characteristic features observed in the solute breakthrough and equilibrium between liquid and solid phase. Specific to the closed‐flow mode is the recirculation of the effluent to the inflow via a mixing vessel. Depending on the ratio of volumes of mixing vessel and water‐filled pore space, a damped oscillating solute concentration emerges in the effluent and mixing vessel. The oscillation characteristics, e.g. frequency, amplitude and damping, allow for the investigation of solute transport in a similar fashion as known for classical open‐flow column experiments. However, the closed loop conserves substances released during transport within the system. In this way, solute and porous medium can equilibrate with respect to physicochemical conditions. With this paper, the features emerging in the breakthrough curves of saturated column experiments run in closed‐flow mode and methods of evaluation are illustrated under experimental boundary conditions forcing the appearance of oscillations. We demonstrate that the effective pore water volume and the pumping rate can be determined from a conservative tracer breakthrough curve uniquely. In this way, external preconditioning of the material, e.g. drying, can be avoided. A reactive breakthrough experiment revealed a significant increase in the pore water pH value as a consequence of the closed loop. These results highlight the specific impact of the closed mass balance. Furthermore, the basis for the modeling of closed‐flow experiments is given by the derivation of constitutive equations and numerical implementation, validated with the presented experiments. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-04T12:02:26.00204-05:0
      DOI: 10.1002/2015WR018317
       
  • A data fusion‐based drought index
    • Abstract: Drought and water stress monitoring plays an important role in the management of water resources, especially during periods of extreme climate conditions. Here, a data fusion based drought index (DFDI) has been developed and analyzed for three different locations of varying landuse and climate regimes in Australia. The proposed index comprehensively considers all types of drought through a selection of indices and proxies associated with each drought type. In deriving the proposed index, weekly data from three different data sources (OzFlux Network, Asia‐Pacific Water Monitor, and MODIS‐Terra satellite) were employed to first derive commonly used individual standardized drought indices (SDIs), which were then grouped using an advanced clustering method. Next, three different multivariate methods (principal component analysis, factor analysis, and independent component analysis) were utilized to aggregate the SDIs located within each group. For the two clusters in which the grouped SDIs best reflected the water availability and vegetation conditions, the variables were aggregated based on an averaging between the standardized first principal components of the different multivariate methods. Then, considering those two aggregated indices as well as the classifications of months (dry/wet months and active/non‐active months), the proposed DFDI was developed. Finally, the symbolic regression method was used to derive mathematical equations for the proposed DFDI. The results presented here show that the proposed index has revealed new aspects in water stress monitoring which previous indices were not able to, by simultaneously considering both hydro‐meteorological and ecological concepts to define the real water stress of the study areas. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-04T12:01:37.18164-05:0
      DOI: 10.1002/2015WR017834
       
  • Pore‐scale displacement mechanisms as a source of hysteresis for
           two‐phase flow in porous media
    • Abstract: The macroscopic description of the hysteretic behavior of two‐phase flow in porous media remains a challenge. It is not obvious how to represent the underlying pore scale processes at the Darcy‐scale in a consistent way. Darcy‐scale thermodynamic models do not completely eliminate hysteresis and our findings indicate that the shape of displacement fronts is an additional source of hysteresis that has not been considered before. This is a shortcoming because effective process behavior such as trapping efficiency of CO2 or oil production during water flooding are directly linked to pore scale displacement mechanisms with very different front shape such as capillary fingering, flat frontal displacement or cluster growth. Here we introduce fluid topology, expressed by the Euler characteristic of the non‐wetting phase (χn), as a shape measure of displacement fronts. Using two high‐quality data sets obtained by fast X‐ray tomography we show that χn is hysteretic between drainage and imbibition and characteristic for the underlying displacement pattern. In a more physical sense the Euler characteristic can be interpreted as a parameter describing local fluid connectedness. It may provide the closing link between a topological characterization and macroscopic formulations of two‐phase immiscible displacement in porous rock. Since fast X‐ray tomography is currently becoming a mature technique, we expect a significant growth in high quality datasets of real time fluid displacement processes in the future. The novel measures of fluid topology presented here have the potential to become standard metrics needed to fully explore them. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-04T11:57:04.227224-05:
      DOI: 10.1002/2015WR018254
       
  • Simultaneous sorption and mechanical entrapment during polymer flow
           through porous media
    • Authors: R. Farajzadeh; P. Bedrikovetsky, M. Lotfollahi, L.W. Lake
      Abstract: Physical adsorption and mechanical entrapment are two major causes of polymer retention in porous media. Physical adsorption is considered an equilibrium process and is often modelled by assuming a Langmuir isotherm. The outcome is a steady‐state pressure response because the permeability reduction is also accounted for by adsorption. However, some experimental data show gradual increase of pressure with time implying that polymer retention is a time‐dependent process. We discuss simultaneous effect of sorption and mechanical entrapment on the polymer retention in porous media. An exact solution for 1‐D flow problem for the case of constant filtration coefficient and Langmuir‐sorption isotherm, including explicit formulae for breakthrough concentration and pressure drop across the core is derived. The general model with a varying filtration coefficient was successfully matched with experimental data confirming the occurrence of simultaneous sorption with deep‐bed filtration during polymer flow in porous media. In the absence of mechanical entrapment, the physical adsorption causes delay in the polymer front and does not affect the polymer concentration behind the front. Addition of mechanical entrapment results in slow recovery of the injected concentration at the outlet (for a varying filtration coefficient) or reaching to a steady‐state concentration, which is only a fraction of the injected concentration (for a constant filtration coefficient). Accurate assessment and quantification of the polymer retention requires both pressure and effluent concentration data at the outlet of the porous medium. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-01T19:17:25.040441-05:
      DOI: 10.1002/2015WR017885
       
  • Describing the catchment‐averaged precipitation as a stochastic
           process improves parameter and input estimation
    • Abstract: Rainfall input uncertainty is one of the major concerns in hydrological modeling. Unfortunately, during inference, input errors are usually neglected, which can lead to biased parameters and implausible predictions. Rainfall multipliers can reduce this problem but still fail when the observed input (precipitation) has a different temporal pattern from the true one or if the true non‐zero input is not detected. In this study we propose an improved input error model which is able to overcome these challenges and to assess and reduce input uncertainty. We formulate the average precipitation over the watershed as a stochastic input process (SIP) and, together with a model of the hydrosystem, include it in the likelihood function. During statistical inference we use “noisy” input (rainfall) and output (runoff) data to learn about the “true” rainfall, model parameters, and runoff. We test the methodology with the rainfall‐discharge dynamics of a small urban catchment. To assess its advantages, we compare SIP with simpler methods of describing uncertainty within statistical inference: i) standard least squares (LS), ii) bias description (BD), and iii) rainfall multipliers (RM). We also compare two scenarios: accurate versus inaccurate forcing data. Results show that when inferring the input with SIP and using inaccurate forcing data, the whole‐catchment precipitation can still be realistically estimated and thus physical parameters can be “protected” from the corrupting impact of input errors. While correcting the output rather than the input, BD inferred similarly unbiased parameters. This is not the case with LS and RM. During validation, SIP also delivers realistic uncertainty intervals for both rainfall and runoff. Thus, the technique presented is a significant step towards better quantifying input uncertainty in hydrological inference. As a next step, SIP will have to be combined with a technique addressing model structure uncertainty. This article is protected by copyright. All rights reserved.
      PubDate: 2016-03-01T19:16:34.22974-05:0
      DOI: 10.1002/2015WR017871
       
  • Remote Monitoring of Volumetric Discharge Employing Bathymetry Determined
           from Surface Turbulence Metrics
    • Authors: E. D. Johnson; E. A. Cowen
      Abstract: Current methods employed by the United States Geological Survey (USGS) to measure river discharge are manpower‐intensive, expensive, and during high flow events require field personnel to work in dangerous conditions. Indirect methods of estimating river discharge, which involve the use of extrapolated rating curves, can result in gross error during high flow conditions due to extrapolation error and/or bathymetric change. Our goal is to develop a remote method of monitoring volumetric discharge that reduces costs at the same or improved accuracy compared with current methods, while minimizing risk to field technicians. We report the results of Large‐Scale Particle Image Velocimetry (LSPIV) and Acoustic Doppler Velocimetry (ADV) measurements conducted in a wide open‐channel under a range of flow conditions, i.e. channel aspect ratio (B/H = 6.6 ‐ 31.9), Reynolds number (ReH = 4,950 ‐ 73,800) and Froude number (Fr = 0.04 ‐ 0.46). Experiments were carried out for two different channel cross‐sections (rectangular and asymmetric‐compound) and two bathymetric roughness conditions (smooth glass and rough gravel bed). The results show that the mean surface velocity normalized by the depth‐averaged velocity (the velocity index) decreases with increasing δ*/H, where δ* is the boundary layer displacement thickness) and that the integral length scales, L11,1 and L22,1, calculated on the free‐surface vary predictably with the local flow depth. Remote determination of local depth‐averaged velocity and flow depth over a channel cross‐section yields an estimate of volumetric discharge. This article is protected by copyright. All rights reserved.
      PubDate: 2016-02-26T17:47:39.425876-05:
      DOI: 10.1002/2015WR017736
       
  • Residence times of stream‐groundwater exchanges due to transient
           stream stage fluctuations
    • Authors: James L. McCallum; Margaret Shanafield
      Abstract: The biogeochemical functioning of stream ecosystems is heavily dependent on water and water‐borne nutrient fluxes between the stream itself and the streambed and banks (i. e. the hyporheic zone). The travel time of water exchanges through the hyporheic zone has been investigated previously; however, these studies have primarily modelled exchanges under steady state conditions assuming spatial pressure variations. This assumes that the hydraulic gradients that drive the exchanges are maintained the whole time the stream water remains in the bed or banks, which is unrealistic. Therefore, in this study we use a transient approach to investigate residence time distributions (RTDs) of bank inflow and bank outflow during both regular, diurnal stream stage variations and storm flow events. We demonstrate that RTDs reflect the timing and magnitude bank inflows, rather than smooth RTDs. We also show that small percentages of water from a given bank inflow event may be present in bank outflows for long periods of time, due to dispersion and diffusion within the bank, and lower rates of bank outflow, relative to bank inflow. This is apparent in the synthetic model of a single storm flow event, where 10% remained in the bank after 50 days. Additionally, residence times for a given bank inflow event are longer when repeated events occur, because the bank outflows from one event are “interrupted” by an increase in stream stage during a successive event. For example, field data capturing events of variable timing and magnitude showed that 70 days after each of three storm flow events occurred, 40, 12 and 30% of the bank inflow event remained in the banks. These cases indicate that bank exchanges are temporally dynamic and the RTDs of return flows can have significant tailing, which will dictate rates of nutrient exchange within the near‐stream environment. This article is protected by copyright. All rights reserved.
      PubDate: 2016-02-26T17:46:52.541043-05:
      DOI: 10.1002/2015WR017441
       
  • Mapping Land Water and Energy Balance Relations Through Conditional
           Sampling of Remote Sensing Estimates of Atmospheric Forcing and Surface
           States
    • Authors: Leila Farhadi; Dara Entekhabi, Guido Salvucci
      Abstract: In this study we develop and apply a mapping estimation capability for key unknown parameters that link the surface water and energy balance equations. The method is applied to the Gourma region in West Africa. The accuracy of the estimation method at point scale was previously examined using flux tower data. In this study the capability is scaled to be applicable with remotely sensed data products and hence allow mapping. Parameters of the system are estimated through a process that links atmospheric forcing (precipitation and incident radiation), surface states and unknown parameters. Based on conditional averaging of land surface temperature and moisture states respectively, a single objective function is posed that measures moisture and temperature dependent errors solely in terms of observed forcings and surface states. This objective function is minimized with respect to parameters to identify evapotranspiration and drainage models and estimate water and energy balance flux components. The uncertainty of the estimated parameters (and associated statistical confidence limits) is obtained through the inverse of Hessian of the objective function, which is an approximation of the covariance matrix. This calibration free method is applied to the mesoscale region of Gourma using multi‐platform remote sensing data. The retrievals are verified against tower‐flux field site data and physiographic characteristics of the region. The focus is to find the functional form of the evaporative fraction dependence on soil moisture, a key closure function for surface and subsurface heat and moisture dynamics, using remote sensing data. This article is protected by copyright. All rights reserved.
      PubDate: 2016-02-26T17:46:32.333544-05:
      DOI: 10.1002/2015WR017680
       
  • Matching ecohydrological processes and scales of banded vegetation
           patterns in semi‐arid catchments
    • Authors: Athanasios Paschalis; Gabriel G. Katul, Simone Fatichi, Gabriele Manoli, Peter Molnar
      Abstract: While the claim that water‐carbon interactions result in spatially coherent vegetation patterning is rarely disputed in many arid and semi‐arid regions, the significance of the detailed water pathways and other high frequency variability remain an open question. How the short temporal scale meteorological fluctuations form the long term spatial variability of available soil water in complex terrains due to the various hydrological, land surface and vegetation dynamic feedbacks, frames the scope of the work here. Knowledge of the detailed mechanistic feedbacks between soil, plants and the atmosphere will lead to advances in our understanding of plant water availability in arid and semi‐arid ecosystems and will provide insights for future model development concerning vegetation pattern formation. In this study, quantitative estimates of water fluxes and vegetation productivity are provided for a semi‐arid ecosystem with established vegetation bands on hillslopes using numerical simulations. A state‐of‐the‐science process based ecohydrological model is used, which resolves hydrological and plant physiological processes at the relevant space and time scales, for relatively small periods (e.g. decades) of mature ecosystems (i.e. spatially static vegetation distribution). To unfold the mechanisms that shape the spatial distribution of soil moisture, plant productivity and the relevant surface/subsurface and atmospheric water fluxes, idealized hillslope numerical experiments are constructed, where the effects of soil‐type, slope steepness and overland flow accumulation area are quantified. Those mechanisms are also simulated in the presence of complex topography features on landscapes. The main results are: (a) Short temporal scale meteorological variability and accurate representation of the scales at which each ecohydrological process operates are crucial for the estimation of the spatial variability of soil water availability to the plant root zone; (b) Water fluxes such as evapotranspiration, infiltration, runoff‐runon and subsurface soil water movement have a dynamic short temporal scale behavior that determines the long term spatial organization of plant soil water availability in ecosystems with established vegetation patterns; (c) Hypotheses concerning the hydrological responses that can lead to vegetation pattern formation have to accommodate realistic and physically based representations of the fast dynamics of key ecohydrological fluxes. This article is protected by copyright. All rights reserved.
      PubDate: 2016-02-25T18:16:09.472964-05:
      DOI: 10.1002/2015WR017679
       
  • Groundwater exchanges near a channelized versus unmodified stream mouth
           discharging to a subalpine lake
    • Authors: Jim Constantz; Ramon Naranjo, Richard G. Niswonger, Kip Allander, Bethany Neilson, Donald Rosenberry, David W. Smith, Celia Z. Rosecrans, David A. Stonestrom
      Abstract: The terminus of a stream flowing into a larger river, pond, lake, or reservoir is referred to as the stream‐mouth reach or simply the stream mouth. The terminus is often characterized by rapidly changing thermal and hydraulic conditions that result in abrupt shifts in surface‐water/groundwater (sw/gw) exchange patterns, creating the potential for unique biogeochemical processes and ecosystems. Worldwide shoreline development is changing stream‐lake interfaces through channelization of stream mouths, i.e., channel straightening and bank‐stabilization to prevent natural meandering at the shoreline. In the central Sierra Nevada (US), Lake Tahoe's shoreline has an abundance of both ‘unmodified' (i.e., not engineered though potentially impacted by broader watershed engineering) and channelized stream mouths. Two representative stream mouths along the lake's north shore, one channelized and one unmodified, were selected to compare and contrast water and heat exchanges. Hydraulic and thermal properties were monitored during separate campaigns in September 2012 and 2013 and sw/gw exchanges were estimated within the stream mouth‐shoreline continuum. Heat‐ and water‐flow patterns indicated clear differences in the channelized versus the unmodified stream mouth. For the channelized stream mouth, relatively modulated, cool‐temperature, low‐velocity longitudinal streambed flows discharged offshore beneath warmer buoyant lakeshore water. In contrast, a seasonal barrier bar formed across the unmodified stream mouth, creating higher‐velocity subsurface flow paths and higher diurnal temperature variations relative to shoreline water. As a consequence, channelization altered sw/gw exchanges potentially altering biogeochemical processing and ecological systems in and near the stream mouth. This article is protected by copyright. All rights reserved.
      PubDate: 2016-02-22T18:22:22.770132-05:
      DOI: 10.1002/2015WR017013
       
  • Bootstrap rank‐ordered conditional mutual information
           (broCMI)—A nonlinear input variable selection method for water
           resources modeling
    • Authors: John Quilty; Jan Adamowski, Bahaa Khalil, Maheswaran Rathinasamy
      Abstract: The input variable selection problem has recently garnered much interest in the time series modeling community, especially within water resources applications, demonstrating that information theoretic (nonlinear) based input variable selection algorithms such as partial mutual information (PMI) selection (PMIS) provide an improved representation of the modeled process when compared to linear alternatives such as partial correlation input selection (PCIS). PMIS is a popular algorithm for water resources modeling problems considering nonlinear input variable selection; however, this method requires the specification of two nonlinear regression models, each with parametric settings that greatly influence the selected input variables. Other attempts to develop input variable selection methods using conditional mutual information (CMI) (an analogue to PMI) have been formulated under different parametric pretenses such as k nearest‐neighbour (KNN) statistics or kernel density estimates (KDE). In this paper we introduce a new input variable selection method based on CMI that uses a non‐parametric multivariate continuous probability estimator based on Edgeworth approximations (EA). We improve the EA method by considering the uncertainty in the input variable selection procedure by introducing a bootstrap resampling procedure that uses rank statistics to order the selected input sets; we name our proposed method bootstrap rank‐ordered CMI (broCMI). We demonstrate the superior performance of broCMI when compared to CMI based alternatives (EA, KDE, and KNN), PMIS, and PCIS input variable selection algorithms on a set of seven synthetic test problems and a real‐world urban water demand (UWD) forecasting experiment in Ottawa, Canada. This article is protected by copyright. All rights reserved.
      PubDate: 2016-02-22T18:21:10.7609-05:00
      DOI: 10.1002/2015WR016959
       
  • A sociohydrological model for smallholder farmers in Maharashtra, India
    • Authors: Saket Pande; Hubert H. G. Savenije
      Abstract: We present a socio‐hydrological model that can help us to better understand the system dynamics of a smallholder farmer. It couples the dynamics of the six main assets of a typical smallholder farmer: water storage capacity, capital, livestock, soil fertility and grazing access. The hydro‐climatic variability, which is a main driver and source of uncertainty of the smallholder system, is accounted for at sub‐annual scale. The model incorporates rule‐based adaptation mechanisms of smallholders (for example: adjusting expenditures on food and fertilizers, selling livestocks etc.) when farmers face adverse socio‐hydrological conditions, such as low annual rainfall, occurrence of dry spells or variability of input or commodity prices. We have applied the model to analyze the socio‐hydrology of a cash‐crop producing smallholder in Maharashtra, India, in a semi‐synthetic case study setting. Of late, this region has witnessed many suicides of farmers who could not extricate themselves out of the debt trap. These farmers lacked irrigation and were susceptible to fluctuating commodity prices and climatic variability. We studied the sensitivity of a smallholder's capital, an indicator of smallholder wellbeing, to 2 types of cash crops (cotton and sugarcane), water storage capacity, availability of irrigation, initial capital that a smallholder starts with, prevalent wage rates and access to grazing. We found that i) smallholders with low water storage capacities and no irrigation are most susceptible to distress, ii) a smallholder's well being is low at low wage rates, iii) wage rate is more important than absolution of debt, iv) well being is sensitive to water storage capacity up to a certain level and v) wellbeing increases with increasing area available for livestock grazing. Our results indicate that government intervention to absolve the debt of farmers or to invest in local storage to buffer rainfall variability may not be enough. In addition alternative sources of income may need to be provided, for instance by ensuring minimum wages or by providing more access to grazing areas. This article is protected by copyright. All rights reserved.
      PubDate: 2016-02-22T18:20:46.290325-05:
      DOI: 10.1002/2015WR017841
       
  • Fluid flow in porous media with rough pore‐solid interface
    • Authors: Behzad Ghanbarian; Allen G. Hunt, Hugh Daigle
      Abstract: Quantifying fluid flow through porous media hinges on the description of permeability, a property of considerable importance in many fields ranging from oil and gas exploration to hydrology. A common building block for modeling porous media permeability is consideration of fluid flow through tubes with circular cross section described by Poiseuille's law in which flow discharge is proportional to the 4th power of the tube's radius. In most natural porous media, pores are neither cylindrical nor smooth, they often have an irregular cross section and rough surfaces. This study presents a theoretical scaling of Poiseuille's approximation for flow in pores with irregular rough cross section quantified by a surface fractal dimension Ds2. The flow rate is a function of the average pore radius to the power 2(3‐Ds2) instead of 4 in the original Poiseuille's law. Values of Ds2 range from 1 to 2, hence, the power in the modified Poiseuille's approximation varies between 4 and 2, indicating that flow rate decreases as pore surface roughness (and surface fractal dimension Ds2) increases. We also proposed pore length‐radius relations for isotropic and anisotropic fractal porous media. The new theoretical derivations are compared with standard approximations and with experimental values of relative permeability. The new approach results in substantially improved prediction of relative permeability of natural porous media relative to the original Poiseuille equation. This article is protected by copyright. All rights reserved.
      PubDate: 2016-02-22T18:17:37.421221-05:
      DOI: 10.1002/2015WR017857
       
  • Probabilistic collocation method for strongly nonlinear problems: 3.
           Transform by time
    • Authors: Qinzhuo Liao; Dongxiao Zhang
      Abstract: [1] The probabilistic collocation method (PCM) has drawn wide attention for stochastic analysis recently. Its results may become inaccurate in case of a strongly nonlinear relation between random parameters and model responses. To tackle this problem, we proposed a location‐based transformed PCM (xTPCM) and a displacement‐based transformed PCM (dTPCM) in previous parts of this series [Liao and Zhang, 2013; Liao and Zhang, 2014]. Making use of the transform between response and space, the above two methods, however, have certain limitations. In this study, we introduce a time‐based transformed PCM (tTPCM) employing the transform between response and time. We conduct numerical experiments to investigate its performance in uncertainty quantification. The results show that the tTPCM greatly improves the accuracy of the traditional PCM in a cost‐effective manner and is more general and convenient than the xTPCM/dTPCM. This article is protected by copyright. All rights reserved.
      PubDate: 2016-02-17T18:43:57.185272-05:
      DOI: 10.1002/2015WR017724
       
  • How well will the Surface Water and Ocean Topography (SWOT) mission
           observe global reservoirs?
    • Authors: Kurt C. Solander; John T. Reager, James S. Famiglietti
      Abstract: Accurate observations of global reservoir storage are critical to understand the availability of managed water resources. By enabling estimates of surface water area and height for reservoir sizes exceeding 250 m2 at a maximum repeat orbit of up to 21‐days, the NASA Surface Water and Ocean Topography (SWOT) satellite mission (anticipated launch date 2020) is expected to greatly improve upon existing reservoir monitoring capabilities. It is thus essential that spatial and temporal measurement uncertainty for water bodies is known a priori to maximize the utility of SWOT observations as the data are acquired. In this study, we evaluate SWOT reservoir observations using a three‐pronged approach that assesses temporal aliasing, errors due to specific reservoir spatial properties, and SWOT performance over actual reservoirs using a combination of in‐situ and simulated reservoir observations from the SWOTsim instrument simulator. Results indicate temporal errors to be less than 5% for the smallest reservoir sizes (< 10 km2) with errors less than 0.1% for larger sizes (>100 km2). Surface area and height errors were found to be minimal (area
      PubDate: 2016-02-13T03:37:19.678579-05:
      DOI: 10.1002/2015WR017952
       
  • Tension‐saturated and unsaturated flows from line sources in
           subsurface irrigation: Riesenkampf's and Philip's solutions revisited
    • Authors: A.R. Kacimov; Yu.V. Obnosov
      Abstract: Riesenkampf's (1938), R‐38 (referred to here as R‐38), analytical solution for steady 2‐D flow from a buried line source in a homogeneous Green‐Ampt soil, with a wetting plume bounded by a free surface (capillary fringe), is compared with Philip's (1969), (P‐69), one for genuinely‐unsaturated wetting of Gardner's infinite‐extension soil. Conformal mappings are used in R‐38, from which we derived the flow net, pore‐water isobars, isochrones, fields of Darcian velocity and resultant force acting on saturated porous skeleton, fine geometry (shape and size) of the constant‐head contour encompassing a mole‐emitter or leaky‐pipe, as well as the dependence of the total discharge per unit pipe length on uniform pressure in the pipe, capillarity of the soil, radius of the pipe and saturated hydraulic conductivity. An ovalic “water table” isobar, encompassing P‐69 source, is compared with one of R‐38 for a fixed discharge and saturated conductivity but adjusted sorptive numbers. The Whisler‐Bouwer (1970) relation between the static height of capillary rise and sorptive number is shown to give a good match between R‐38 and P‐69 isobars. This allows to use R‐38 in the source vicinity and P‐69 in the far‐field zone. Computer algebra (Mathematica) routines are used for visualization of the known and extended R‐38 and P‐69 solutions. This article is protected by copyright. All rights reserved.
      PubDate: 2016-02-12T03:17:55.211355-05:
      DOI: 10.1002/2015WR018221
       
  • Uncertainty in hydrological signatures for gauged and ungauged catchments
    • Authors: Ida K. Westerberg; Thorsten Wagener, Gemma Coxon, Hilary K. McMillan, Attilio Castellarin, Alberto Montanari, James Freer
      Abstract: Reliable information about hydrological behavior is needed for water‐resource management and scientific investigations. Hydrological signatures quantify catchment behavior as index values, and can be predicted for ungauged catchments using a regionalization procedure. The prediction reliability is affected by data uncertainties for the gauged catchments used in prediction and by uncertainties in the regionalization procedure. We quantified signature uncertainty stemming from discharge data uncertainty for 43 UK catchments and propagated these uncertainties in signature regionalization, while accounting for regionalization uncertainty with a weighted‐pooling‐group approach. Discharge uncertainty was estimated using Monte Carlo sampling of multiple feasible rating curves. For each sampled rating curve, a discharge time series was calculated and used in deriving the gauged signature uncertainty distribution. We found that the gauged uncertainty varied with signature type, local measurement conditions and catchment behavior, with the highest uncertainties (median relative uncertainty ±30–40% across all catchments) for signatures measuring high‐ and low‐flow magnitude and dynamics. Our regionalization method allowed assessing the role and relative magnitudes of the gauged and regionalized uncertainty sources in shaping the signature uncertainty distributions predicted for catchments treated as ungauged. We found that 1) if the gauged uncertainties were neglected there was a clear risk of over‐conditioning the regionalization inference, e.g. by attributing catchment differences resulting from gauged uncertainty to differences in catchment behavior, and 2) uncertainty in the regionalization results was lower for signatures measuring flow distribution (e.g. mean flow) than flow dynamics (e.g. autocorrelation), and for average flows (and then high flows) compared to low flows. This article is protected by copyright. All rights reserved.
      PubDate: 2016-02-02T18:01:28.709247-05:
      DOI: 10.1002/2015WR017635
       
  • Quantifying the fate of agricultural nitrogen in an unconfined aquifer:
           Stream‐based observations at three measurement scales
    • Abstract: We compared three stream‐based sampling methods to study the fate of nitrate in groundwater in a coastal plain watershed: point measurements beneath the streambed, seepage blankets (novel seepage‐meter design), and reach mass‐balance. The methods gave similar mean groundwater seepage rates into the stream (0.3‐0.6 m/day) during two 3‐4 day field campaigns despite an order of magnitude difference in stream discharge between the campaigns. At low flow, estimates of flow‐weighted mean nitrate concentrations in groundwater discharge ([NO3‐]FWM) and nitrate flux from groundwater to the stream decreased with increasing degree of channel influence and measurement scale, i.e., [NO3‐]FWM was 654, 561, and 451 µM for point, blanket, and reach mass‐balance sampling, respectively. At high flow the trend was reversed, likely because reach mass‐balance captured inputs from shallow transient high‐nitrate flow paths while point and blanket measurements did not. Point sampling may be better suited to estimating aquifer discharge of nitrate, while reach mass‐balance reflects full nitrate inputs into the channel (which at high flow may be more than aquifer discharge due to transient flowpaths, and at low flow may be less than aquifer discharge due to channel‐based nitrate removal). Modeling dissolved N2 from streambed samples suggested (1) about half of groundwater nitrate was denitrified prior to discharge from the aquifer, and (2) both extent of denitrification and initial nitrate concentration in groundwater (700‐1300 µM) were related to land use, suggesting these forms of streambed sampling for groundwater can reveal watershed spatial relations relevant to nitrate contamination and fate in the aquifer. This article is protected by copyright. All rights reserved.
      PubDate: 2016-02-02T18:00:35.724819-05:
      DOI: 10.1002/2015WR017599
       
  • Groundwater transit time distribution and mean from streambed sampling in
           an agricultural coastal plain watershed, North Carolina, USA
    • Authors: Troy E. Gilmore; David P. Genereux, D. Kip Solomon, John E. Solder
      Abstract: We measured groundwater apparent age (τ) and seepage rate (v) in a sandy streambed using point‐scale sampling and seepage blankets (a novel seepage meter). We found very similar MTT estimates from streambed point sampling in a 58 m reach (29 years) and a 2.5 km reach (31 years). The TTD for groundwater discharging to the stream was best fit by a gamma distribution model and was very similar for streambed point sampling in both reaches. Between adjacent point‐scale and seepage blanket samples, water from the seepage blankets was generally younger, largely because blanket samples contained a fraction of “young” stream water. Correcting blanket data for the stream water fraction brought τ estimates for most blanket samples closer to those for adjacent point samples. The MTT estimates from corrected blanket data were in good agreement with those from sampling streambed points adjacent to the blankets. Collectively, agreement among age‐dating tracers, general accord between tracer data and piston‐flow model curves, and large groundwater age gradients in the streambed, suggested that the piston flow apparent ages were reasonable estimates of the groundwater transit times for most samples. Overall, our results from two field campaigns suggest that groundwater collected in the streambed can provide reasonable estimates of apparent age of groundwater discharge, and that MTT can be determined from different age‐dating tracers and by sampling with different groundwater collection devices. Coupled streambed point measurements of groundwater age and groundwater seepage rate represent a novel, reproducible, and effective approach to estimating aquifer TTD and MTT. This article is protected by copyright. All rights reserved.
      PubDate: 2016-02-02T11:07:56.313422-05:
      DOI: 10.1002/2015WR017600
       
  • Influence of soil and climate on root zone storage capacity
    • Abstract: Root zone storage capacity (Sr) is an important variable for hydrology and climate studies, as it strongly influences the hydrological functioning of a catchment and, via evaporation, the local climate. Despite its importance, it remains difficult to obtain a well‐founded catchment representative estimate. This study tests the hypothesis that vegetation adapts its Sr to create a buffer large enough to sustain the plant during drought conditions of a certain critical strength (with a certain probability of exceedance). Following this method, Sr can be estimated from precipitation and evaporative demand data. The results of this 'climate based method' are compared with traditional estimates from soil data for 32 catchments in New Zealand. The results show that the differences between catchments in climate derived catchment representative Sr values are larger than for soil derived Sr values. Using a model experiment we show that the climate derived Sr can better reproduce hydrological regime signatures for humid catchments; for more arid catchments the soil and climate methods perform similarly. This makes the climate based Sr a valuable addition for increasing hydrological understanding and reducing hydrological model uncertainty. This article is protected by copyright. All rights reserved.
      PubDate: 2016-02-02T08:23:42.449484-05:
      DOI: 10.1002/2015WR018115
       
  • Simulating runoff under changing climatic conditions: Revisiting an
           apparent deficiency of conceptual rainfall‐runoff models
    • Authors: Keirnan J. A. Fowler; Murray C. Peel, Andrew W. Western, Lu Zhang, Tim J. Peterson
      Abstract: Hydrologic models have potential to be useful tools in planning for future climate variability. However, recent literature suggests that the current generation of conceptual rainfall runoff models tend to underestimate the sensitivity of runoff to a given change in rainfall, leading to poor performance when evaluated over multi‐year droughts. This research revisited this conclusion, investigating whether the observed poor performance could be due to insufficient model calibration and evaluation techniques. We applied an approach based on Pareto optimality to explore trade‐offs between model performance in different climatic conditions. Five conceptual rainfall runoff model structures were tested in 86 catchments in Australia, for a total of 430 Pareto analyses. The Pareto results were then compared with results from a commonly used model calibration and evaluation method, the Differential Split Sample Test. We found that the latter often missed potentially promising parameter sets within a given model structure, giving a false negative impression of the capabilities of the model. This suggests that models may be more capable under changing climatic conditions than previously thought. Of the 282(347) cases of apparent model failure under the split sample test using the lower (higher) of two model performance criteria trialled, 155(120) were false negatives. We discuss potential causes of remaining model failures, including the role of data errors. Although the Pareto approach proved useful, our aim was not to suggest an alternative calibration strategy, but to critically assess existing methods of model calibration and evaluation. We recommend caution when interpreting split sample results. This article is protected by copyright. All rights reserved.
      PubDate: 2016-02-02T03:03:29.054841-05:
      DOI: 10.1002/2015WR018068
       
  • Enhancing multiple‐point geostatistical modeling: 2. Iterative
           simulation and multiple distance function
    • Authors: Pejman Tahmasebi; Muhammad Sahimi
      Abstract: This series addresses a fundamental issue in multiple‐point statistical (MPS) simulation for generation of realizations of large‐scale porous media. Past methods suffer from the fact that they generate discontinuities and patchiness in the realizations that, in turn, affect their flow and transport properties. Part I of this series addressed certain aspects of this fundamental issue, and proposed two ways of improving of one such MPS method, namely, the cross correlation‐based simulation (CCSIM) method that was proposed by the authors. In the present paper a new algorithm is proposed to further improve the quality of the realizations. The method utilizes the realizations generated by the algorithm introduced in Part I, iteratively removes any possible remaining discontinuities in them, and addresses the problem with honoring hard (quantitative) data, using an error map. The map represents the differences between the patterns in the training image (TI) and the current iteration of a realization. The resulting iterative CCSIM – the iCCSIM algorithm ‐ utilizes a random path and the error map to identify the locations in the current realization in the iteration process that need further “repairing;” that is, those locations at which discontinuities may still exist. The computational time of the new iterative algorithm is considerably lower than one in which every cell of the simulation grid is visited in order to repair the discontinuities. Furthermore, several efficient distance functions are introduced by which one extracts effectively key information from the TIs. To increase the quality of the realizations and extracting the maximum amount of information from the TIs, the distance functions can be used simultaneously. The performance of the iCCSIM algorithm is studied using very complex 2D and 3D examples, including those that are process‐based. Comparison is made between the quality and accuracy of the results with those generated by the original CCSIM algorithm, which demonstrates the superior performance of the iCCSIM. This article is protected by copyright. All rights reserved.
      PubDate: 2016-01-07T18:11:51.293926-05:
      DOI: 10.1002/2015WR017807
       
  • Enhancing multiple‐point geostatistical modeling: 1. Graph theory
           and pattern adjustment
    • Authors: Pejman Tahmasebi; Muhammad Sahimi
      Abstract: In recent years higher‐order geostatistical methods have been used for modeling of a wide variety of large‐scale porous media, such as groundwater aquifers and oil reservoirs. Their popularity stems from their ability to account for qualitative data and the great flexibility that they offer for conditioning the models to hard (quantitative) data, which endow them with the capability for generating realistic realizations of porous formations with very complex channels, as well as features that are mainly a barrier to fluid flow. One group of such models consists of pattern‐based methods that use a set of data points for generating stochastic realizations by which the large‐scale structure and highly‐connected features are reproduced accurately. The cross correlation‐based simulation (CCSIM) algorithm, proposed previously by the authors, is a member of this group that has been shown to be capable of simulating multi‐million cell models in a matter of a few CPU seconds. The method is, however, sensitive to pattern's specifications, such as boundaries and the number of replicates. In this paper the original CCSIM algorithm is reconsidered and two significant improvements are proposed for accurately reproducing large‐scale patterns of heterogeneities in porous media. First, an effective boundary‐correction method based on the graph theory is presented by which one identifies the optimal cutting path/surface for removing the patchiness and discontinuities in the realization of a porous medium. Next, a new pattern adjustment method is proposed that automatically transfers the features in a pattern to one that seamlessly matches the surrounding patterns. The original CCSIM algorithm is then combined with the two methods and is tested using various complex two‐ and three‐dimensional examples. It should, however, be emphasized that the methods that we propose in this paper are applicable to other pattern‐based geostatistical simulation methods. This article is protected by copyright. All rights reserved.
      PubDate: 2016-01-07T18:11:09.582861-05:
      DOI: 10.1002/2015WR017806
       
  • Issue Information
    • Pages: 1541 - 1543
      PubDate: 2016-04-21T08:15:37.890158-05:
      DOI: 10.1002/wrcr.21694
       
  • Evaporation tagging and atmospheric water budget analysis with WRF: A
           regional precipitation recycling study for West Africa
    • Authors: Joel Arnault; Richard Knoche, Jianhui Wei, Harald Kunstmann
      Pages: 1544 - 1567
      Abstract: Regional precipitation recycling is the measure of the contribution of local evaporation E to local precipitation. This study provides a set of two methods developed in the Weather Research and Forecasting WRF model system for investigating regional precipitation recycling mechanisms: (1) tracking of tagged atmospheric water species originating from evaporation in a source region, ie E‐tagging, and (2) three‐dimensional budgets of total and tagged atmospheric water species. These methods are used to quantify the effect of return flow and nonwell vertical mixing neglected in the computation of the bulk precipitation recycling ratio. The developed algorithms are applied to a WRF simulation of the West African Monsoon 2003. The simulated region is characterized by vertical wind shear condition, i.e., southwesterlies in the low levels and easterlies in the mid‐levels, which favors return flow and nonwell vertical mixing. Regional precipitation recycling is investigated in 100 × 100 and 1000 × 1000 km2 areas. A prerequisite condition for evaporated water to contribute to the precipitation process in both areas is that it is lifted to the mid‐levels where hydrometeors are produced. In the 100 × 100 (1000 × 1000) km2 area the bulk precipitation recycling ratio is 0.9 (7.3) %. Our budget analysis reveals that return flow and nonwell vertically mixed outflow increase this value by about +0.2 (2.9) and +0.2 (1.6) %, respectively, thus strengthening the well‐known scale‐dependency of regional precipitation recycling.
      PubDate: 2016-03-04T05:49:58.856989-05:
      DOI: 10.1002/2015WR017704
       
  • River stage influences on uranium transport in a hydrologically dynamic
           groundwater‐surface water transition zone
    • Authors: John M. Zachara; Xingyuan Chen, Chris Murray, Glenn Hammond
      Pages: 1568 - 1590
      Abstract: A well‐field within a uranium (U) plume in the groundwater‐surface water transition zone was monitored for a 3 year period for water table elevation and dissolved solutes. The plume discharges to the Columbia River, which displays a dramatic spring stage surge resulting from snowmelt. Groundwater exhibits a low hydrologic gradient and chemical differences with river water. River water intrudes the site in spring. Specific aims were to assess the impacts of river intrusion on dissolved uranium (Uaq), specific conductance (SpC), and other solutes, and to discriminate between transport, geochemical, and source term heterogeneity effects. Time series trends for Uaq and SpC were complex and displayed large temporal and well‐to‐well variability as a result of water table elevation fluctuations, river water intrusion, and changes in groundwater flow directions. The wells were clustered into subsets exhibiting common behaviors resulting from the intrusion dynamics of river water and the location of source terms. Hot‐spots in Uaq varied in location with increasing water table elevation through the combined effects of advection and source term location. Heuristic reactive transport modeling with PFLOTRAN demonstrated that mobilized Uaq was transported between wells and source terms in complex trajectories, and was diluted as river water entered and exited the groundwater system. While Uaq time‐series concentration trends varied significantly from year‐to‐year as a result of climate‐caused differences in the spring hydrograph, common and partly predictable response patterns were observed that were driven by water table elevation, and the extent and duration of river water intrusion.
      PubDate: 2016-03-04T05:30:18.229136-05:
      DOI: 10.1002/2015WR018009
       
  • Thermal effects of groundwater flow through subarctic fens: A case study
           based on field observations and numerical modeling
    • Pages: 1591 - 1606
      Abstract: Modeling and observation of ground temperature dynamics are the main tools for understanding current permafrost thermal regimes and projecting future thaw. Until recently, most studies on permafrost have focused on vertical ground heat fluxes. Groundwater can transport heat in both lateral and vertical directions but its influence on ground temperatures at local scales in permafrost environments is not well understood. In this study we combine field observations from a subarctic fen in the sporadic permafrost zone with numerical simulations of coupled water and thermal fluxes. At the Tavvavuoma study site in northern Sweden, ground temperature profiles and groundwater levels were observed in boreholes. These observations were used to set up one‐ and two‐dimensional simulations down to 2 m depth across a gradient of permafrost conditions within and surrounding the fen. Two‐dimensional scenarios representing the fen under various hydraulic gradients were developed to quantify the influence of groundwater flow on ground temperature. Our observations suggest that lateral groundwater flow significantly affects ground temperatures. This is corroborated by modeling results that show seasonal ground ice melts 1 month earlier when a lateral groundwater flux is present. Further, although the thermal regime may be dominated by vertically conducted heat fluxes during most of the year, isolated high groundwater flow rate events such as the spring freshet are potentially important for ground temperatures. As sporadic permafrost environments often contain substantial portions of unfrozen ground with active groundwater flow paths, knowledge of this heat transport mechanism is important for understanding permafrost dynamics in these environments.
      PubDate: 2016-03-04T05:16:54.697191-05:
      DOI: 10.1002/2015WR017571
       
  • Integrated time‐lapse geoelectrical imaging of wetland hydrological
           processes
    • Authors: S.S. Uhlemann; J. P. R. Sorensen, A. R. House, P. B. Wilkinson, C. Roberts, D. C. Gooddy, A. M. Binley, J. E. Chambers
      Pages: 1607 - 1625
      Abstract: Wetlands provide crucial habitats, are critical in the global carbon cycle, and act as key biogeochemical and hydrological buffers. The effectiveness of these services is mainly controlled by hydrological processes, which can be highly variable both spatially and temporally due to structural complexity and seasonality. Spatial analysis of 2‐D geoelectrical monitoring data integrated into the interpretation of conventional hydrological data has been implemented to provide a detailed understanding of hydrological processes in a riparian wetland. A two‐layered hydrological system was observed in the peat. In the lower part of the peat, upwelling of deeper groundwater from underlying deposits was considered the driver for a 30% increase in peat resistivity during Winter/Spring. In Spring/Summer there was a 60% decrease in resistivity in the near‐surface peats due to plant transpiration and/or microbial activity. Water exchange between the layers only appeared to be initiated following large drops in the encircling surface water stage. For the first time, we demonstrated that automated interpretation of geoelectrical data can be used to quantify ground movement in the vertical direction. Here, we applied this method to quantify shrink‐swell of expandable soils, affecting hydrological parameters, such as, porosity and permeability. This study shows that an integrated interpretation of hydrological and geophysical data can significantly improve the understanding of wetland hydrological processes. Potentially, this approach can provide the basis for the evaluation of ecosystem services and may aid in the optimization of wetland management strategies.
      PubDate: 2016-03-04T05:19:25.199402-05:
      DOI: 10.1002/2015WR017932
       
  • Simulating California reservoir operation using the classification and
           regression‐tree algorithm combined with a shuffled
           cross‐validation scheme
    • Authors: Tiantian Yang; Xiaogang Gao, Soroosh Sorooshian, Xin Li
      Pages: 1626 - 1651
      Abstract: The controlled outflows from a reservoir or dam are highly dependent on the decisions made by the reservoir operators, instead of a natural hydrological process. Difference exists between the natural upstream inflows to reservoirs and the controlled outflows from reservoirs that supply the downstream users. With the decision maker's awareness of changing climate, reservoir management requires adaptable means to incorporate more information into decision making, such as water delivery requirement, environmental constraints, dry/wet conditions, etc. In this paper, a robust reservoir outflow simulation model is presented, which incorporates one of the well‐developed data‐mining models (Classification and Regression Tree) to predict the complicated human‐controlled reservoir outflows and extract the reservoir operation patterns. A shuffled cross‐validation approach is further implemented to improve CART's predictive performance. An application study of nine major reservoirs in California is carried out. Results produced by the enhanced CART, original CART, and random forest are compared with observation. The statistical measurements show that the enhanced CART and random forest overperform the CART control run in general, and the enhanced CART algorithm gives a better predictive performance over random forest in simulating the peak flows. The results also show that the proposed model is able to consistently and reasonably predict the expert release decisions. Experiments indicate that the release operation in the Oroville Lake is significantly dominated by SWP allocation amount and reservoirs with low elevation are more sensitive to inflow amount than others.
      PubDate: 2016-03-06T07:52:48.33575-05:0
      DOI: 10.1002/2015WR017394
       
  • Global sampling to assess the value of diverse observations in
           conditioning a real‐world groundwater flow and transport model
    • Authors: Joost R. Delsman; Pieter Winters, Alexander Vandenbohede, Gualbert H. P. Oude Essink, Luc Lebbe
      Pages: 1652 - 1672
      Abstract: The use of additional types of observational data has often been suggested to alleviate the ill‐posedness inherent to parameter estimation of groundwater models and constrain model uncertainty. Disinformation in observational data caused by errors in either the observations or the chosen model structure may, however, confound the value of adding observational data in model conditioning. This paper uses the global generalized likelihood uncertainty estimation methodology to investigate the value of different observational data types (heads, fluxes, salinity, and temperature) in conditioning a groundwater flow and transport model of an extensively monitored field site in the Netherlands. We compared model conditioning using the real observations to a synthetic model experiment, to demonstrate the possible influence of disinformation in observational data in model conditioning. Results showed that the value of different conditioning targets was less evident when conditioning to real measurements than in a measurement error‐only synthetic model experiment. While in the synthetic experiment, all conditioning targets clearly improved model outcomes, minor improvements or even worsening of model outcomes was observed for the real measurements. This result was caused by errors in both the model structure and the observations, resulting in disinformation in the observational data. The observed impact of disinformation in the observational data reiterates the necessity of thorough data validation and the need for accounting for both model structural and observational errors in model conditioning. It further suggests caution when translating results of synthetic modeling examples to real‐world applications. Still, applying diverse conditioning data types was found to be essential to constrain uncertainty, especially in the transport of solutes in the model.
      PubDate: 2016-03-06T07:50:53.495596-05:
      DOI: 10.1002/2014WR016476
       
  • Watershed memory at the Coweeta Hydrologic Laboratory: The effect of past
           precipitation and storage on hydrologic response
    • Authors: Fabian Nippgen; Brian L. McGlynn, Ryan E. Emanuel, James M. Vose
      Pages: 1673 - 1695
      Abstract: The rainfall‐runoff response of watersheds is affected by the legacy of past hydroclimatic conditions. We examined how variability in precipitation affected streamflow using 21 years of daily streamflow and precipitation data from five watersheds at the Coweeta Hydrologic Laboratory in southwestern North Carolina, USA. The gauged watersheds contained both coniferous and deciduous vegetation, dominant north and south aspects, and differing precipitation magnitudes. Lag‐correlations between precipitation and runoff ratios across a range of temporal resolutions indicated strong influence of past precipitation (i.e., watershed memory). At all time‐scales, runoff ratios strongly depended on the precipitation of previous time steps. At monthly time scales, the influence of past precipitation was detectable for up to 7 months. At seasonal time scales, the previous season had a greater effect on a season's runoff ratio than the same season's precipitation. At annual time scales, the previous year was equally important for a year's runoff ratio than the same year's precipitation. Estimated watershed storage through time and specifically the previous year's storage state was strongly correlated with the residuals of a regression between annual precipitation and annual runoff, partially explaining observed variability in annual runoff in watersheds with deep soils. This effect was less pronounced in the steepest watershed that also contained shallow soils. We suggest that the location of a watershed on a nonlinear watershed‐scale storage‐release curve can explain differences in runoff during growing and dormant season between watersheds with different annual evapotranspiration.
      PubDate: 2016-03-06T06:30:28.564333-05:
      DOI: 10.1002/2015WR018196
       
  • Characterization of reciprocity gaps from interference tests in fractured
           media through a dual porosity model
    • Pages: 1696 - 1704
      Abstract: We analyze drawdown reciprocity gaps emerging in interference tests performed in a confined fissured karstic formation. Modeling the system as a dual porosity continuum allows characterizing the dynamics of the relative contribution of the connected fractures and the rock matrix to the total flow rate extracted at the pumping wells. Observed lack of reciprocity of drawdowns can then be linked to the occurrence of processes that are not accounted for in the classical flow models based on a single‐continuum representation of the system through flow equations grounded on Darcy's law only. We show that interpreting the system as a dual porosity continuum can cause drawdown reciprocity gaps to emerge as a consequence of local effects associated with an identifiable contribution of the matrix to the total fluid extracted at the well location during pumping. These theoretical results are then employed to identify the contribution to the flow being supplied to the pumping well by the low conductivity matrix constituting the host rock formation, in contrast to that provided by the fractures. An application to data from two interference tests performed at the Hydrogeological Experimental Site (HES) in Poitiers, France, illustrates the approach. We show that, whenever the matrix is assumed to provide a contribution to the total flow rate extracted, nonreciprocity is expected, the latter being linked to the occurrence of a differential drawdown between fracture and matrix at the pumping well. This difference decreases with time in the example presented, displaying a power law late time behavior, with nonreciprocity effects persisting up to remarkably long times.
      PubDate: 2016-03-06T06:29:00.371647-05:
      DOI: 10.1002/2015WR018171
       
  • The effect of loading efficiency on the groundwater response to water
           level changes in shallow lakes and streams
    • Authors: Mark Bakker
      Pages: 1705 - 1715
      Abstract: The loading efficiency (sometimes called the tidal efficiency) is often neglected when simulating the head response in an aquifer to water level changes in lakes and streams. This is not appropriate when the lake or stream only partially penetrates the aquifer. In such cases, the aquifer extends below the lake or stream and is hydraulically connected through a semiconfining layer of lower permeability. The loading efficiency is the ratio between the instantaneous head response below a lake or stream and the water level change in the lake or stream. In sand and clay, whose particles are not cemented together, the instantaneous head response below a stream or lake is nearly equal to the stage change, and the loading efficiency is close to 1. New semianalytic solutions are presented for the groundwater response to water level changes in shallow lakes and streams that account for the loading efficiency of the aquifer. It is shown that the loading efficiency may have a significant effect on the head response. The effect is larger for larger values of the vertical resistance of the semiconfining layer and larger width of the stream and is much more pronounced in confined aquifers than in unconfined aquifers. The importance of the loading efficiency declines with time and with distance from the lake or stream. Graphs are presented that may be used to determine whether a certain combination of parameters gives a significant difference in the head at the lake shore or river bank when the loading efficiency is taken into account.
      PubDate: 2016-03-06T06:29:24.490517-05:
      DOI: 10.1002/2015WR017977
       
  • Imaging of oil layers, curvature and contact angle in a mixed‐wet
           and a water‐wet carbonate rock
    • Authors: Kamaljit Singh; Branko Bijeljic, Martin J. Blunt
      Pages: 1716 - 1728
      Abstract: We have investigated the effect of wettability of carbonate rocks on the morphologies of remaining oil after sequential oil and brine injection in a capillary‐dominated flow regime at elevated pressure. The wettability of Ketton limestone was altered in situ using an oil phase doped with fatty acid which produced mixed‐wet conditions (the contact angle where oil contacted the solid surface, measured directly from the images, θ=180°, while brine‐filled regions remained water‐wet), whereas the untreated rock (without doped oil) was weakly water‐wet (θ=47 ± 9°). Using X‐ray micro‐tomography, we show that the brine displaces oil in larger pores during brine injection in the mixed‐wet system, leaving oil layers in the pore corners or sandwiched between two brine interfaces. These oil layers, with an average thickness of 47 ± 17 µm, may provide a conductive flow path for slow oil drainage. In contrast, the oil fragments into isolated oil clusters/ganglia during brine injection under water‐wet conditions. Although the remaining oil saturation in a water‐wet system is about a factor of two larger than that obtained in the mixed‐wet rock, the measured brine‐oil interfacial area of the disconnected ganglia is a factor of three smaller than that of oil layers.
      PubDate: 2016-03-06T07:51:41.602058-05:
      DOI: 10.1002/2015WR018072
       
  • Relating salt marsh pore water geochemistry patterns to vegetation zones
           and hydrologic influences
    • Authors: Kevan B. Moffett; Steven M. Gorelick
      Pages: 1729 - 1745
      Abstract: Physical, chemical, and biological factors influence vegetation zonation in salt marshes and other wetlands, but connections among these factors could be better understood. If salt marsh vegetation and marsh pore water geochemistry coorganize, e.g., via continuous plant water uptake and persistently unsaturated sediments controlling vegetation zone‐specific pore water geochemistry, this could complement known physical mechanisms of marsh self‐organization. A high‐resolution survey of pore water geochemistry was conducted among five salt marsh vegetation zones at the same intertidal elevation. Sampling transects were arrayed both parallel and perpendicular to tidal channels. Pore water geochemistry patterns were both horizontally differentiated, corresponding to vegetation zonation, and vertically differentiated, relating to root influences. The geochemical patterns across the site were less broadly related to marsh hydrology than to vegetation zonation. Mechanisms contributing to geochemical differentiation included: root‐induced oxidation and nutrient (P) depletion, surface and creek‐bank sediment flushing by rainfall or tides, evapotranspiration creating aerated pore space for partial sediment flushing in some areas while persistently saturated conditions hindered pore water renewal in others, and evapoconcentration of pore water solutes overall. The concentrated pore waters draining to the tidal creeks accounted for 41% of ebb tide solutes (median of 14 elements), including being a potentially toxic source of Ni but a slight sink for Zn, at least during the short, winter study period in southern San Francisco Bay. Heterogeneous vegetation effects on pore water geochemistry are not only significant locally within the marsh but may broadly influence marsh‐estuary solute exchange and ecology.
      PubDate: 2016-03-06T07:50:24.911035-05:
      DOI: 10.1002/2015WR017406
       
  • Theory and generation of conditional, scalable sub‐Gaussian random
           fields
    • Authors: M. Panzeri; M. Riva, A. Guadagnini, S.P. Neuman
      Pages: 1746 - 1761
      Abstract: Many earth and environmental (as well as a host of other) variables, Y, and their spatial (or temporal) increments, ΔY, exhibit non‐Gaussian statistical scaling. Previously we were able to capture key aspects of such non‐Gaussian scaling by treating Y and/or ΔY as sub‐Gaussian random fields (or processes). This however left unaddressed the empirical finding that whereas sample frequency distributions of Y tend to display relatively mild non‐Gaussian peaks and tails, those of ΔY often reveal peaks that grow sharper and tails that become heavier with decreasing separation distance or lag. Recently we proposed a generalized sub‐Gaussian model (GSG) which resolves this apparent inconsistency between the statistical scaling behaviors of observed variables and their increments. We presented an algorithm to generate unconditional random realizations of statistically isotropic or anisotropic GSG functions and illustrated it in two dimensions. Most importantly, we demonstrated the feasibility of estimating all parameters of a GSG model underlying a single realization of Y by analyzing jointly spatial moments of Y data and corresponding increments, ΔY. Here, we extend our GSG model to account for noisy measurements of Y at a discrete set of points in space (or time), present an algorithm to generate conditional realizations of corresponding isotropic or anisotropic random fields, introduce two approximate versions of this algorithm to reduce CPU time, and explore them on one and two‐dimensional synthetic test cases.
      PubDate: 2016-03-06T07:50:04.996209-05:
      DOI: 10.1002/2015WR018348
       
  • Using time scales to characterize phytoplankton assemblages in a deep
           
    • Pages: 1762 - 1780
      Abstract: A combination of field observations and 3‐D hydrodynamic simulations were used to identify the phytoplankton species and to estimate the various time scales of the dominant physical and biological processes in Lake Iseo, a deep subalpine lake located in northern Italy, during a stratified period (July 2010). By ordering the rate processes time scales, we derive a phytoplankton patch categorization and growth interpretation that provides a general framework for the spatial distribution of phytoplankton concentration in Lake Iseo and illuminates the characteristics of their ecological niches. The results show that the diurnal surface layer was well mixed, received strong diurnal radiation, had low phosphorus concentrations and the phytoplankton biomass was sustained by the green alga Sphaerocystis schroeterii. The vertical mixing time scales were much shorter than horizontal mixing time scales causing a depth‐uniform chlorophyll a concentration. The horizontal patch scale was determined by horizontal dispersion balancing the phytoplankton growth time scale, dictating the success of the observed green algae. The strongly stratified nutrient‐rich metalimnion had mild light conditions and Diatoma elongatum and Planktothrix rubescens made up the largest proportions of the total phytoplankton biomass at the intermediate and deeper metalimnetic layers. The vertical transport time scales were much shorter than horizontal transport and vertical dispersion leading to growth niche for the observed phytoplankton. The study showed that time‐scale hierarchy mandates the essential phytoplankton attributes or traits for success in a particular section of the water column and/or water body.
      PubDate: 2016-03-07T08:01:56.391856-05:
      DOI: 10.1002/2015WR017555
       
  • Effects of soil spatial variability at the hillslope and catchment scales
           on characteristics of rainfall‐induced landslides
    • Authors: Linfeng Fan; Peter Lehmann, Dani Or
      Pages: 1781 - 1799
      Abstract: Spatial variations in soil properties affect key hydrological processes, yet their role in soil mechanical response to hydro‐mechanical loading is rarely considered. This study aims to fill this gap by systematically quantifying effects of spatial variations in soil type and initial water content on rapid rainfall‐induced shallow landslide predictions at the hillslope‐ and catchment‐scales. We employed a physically‐based landslide triggering model that considers mechanical interactions among soil columns governed by strength thresholds. At the hillslope scale, we found that the emergence of weak regions induced by spatial variations of soil type and initial water content resulted in early triggering of landslides with smaller volumes of released mass relative to a homogeneous slope. At the catchment scale, initial water content was linked to a topographic wetness index, whereas soil type varied deterministically with soil depth considering spatially correlated stochastic components. Results indicate that a strong spatial organization of initial water content delays landslide triggering, whereas spatially linked soil type with soil depth promoted landslide initiation. Increasing the standard deviation and correlation length of the stochastic component of soil type increases landslide volume and hastens onset of landslides. The study illustrates that for similar external boundary conditions and mean soil properties, landslide characteristics vary significantly with soil variability, hence it must be considered for improved landslide model predictions.
      PubDate: 2016-03-11T06:40:34.250049-05:
      DOI: 10.1002/2015WR017758
       
  • Impact of scale/resolution on evapotranspiration from Landsat and MODIS
           images
    • Authors: Vivek Sharma; Ayse Kilic, Suat Irmak
      Pages: 1800 - 1819
      Abstract: Understanding the role of landscape heterogeneity and its influence on the scaling behavior of surface fluxes as observed by satellite sensors with different spatial resolutions is a critical need to investigate. In this study, the effects of pixel scales on ETc estimation and other parameters that are used to calculate ETc were investigated over different vegetation surfaces in south central Nebraska, USA. Surface Energy Balance System (SEBS) was used to estimate spatially distributed ETc by combining ground‐based meteorological data for Landsat and MODIS imagery. The estimated surface energy fluxes were compared and validated to the measured Bowen Ratio Energy Balance System (BREBS) ETc fluxes. Validation results showed that Landsat has more preferable spatial resolution (30 m) to map and analyze ETc; regression models explained 91% of the variability in the observed data (RMSD = 0.064 mm/h; MBE = 0.04 mm/h). However, for MODIS‐based ETc, the regression model explained only 59% of the variability in observed ETc with a larger error (RMSD = 0.17 mm/h; MBE = 0.15 mm/h). MODIS‐based ETc was about 31% higher than the measured ETc. Imperfect assessment in MODIS‐based retrievals is due to the underlying assumption of spatial heterogeneity and coarser sensor pixel scale (500 m), which was summarized by up‐scaling the Landsat images to MODIS images using output flux aggregation and input up‐scaling procedure using simple average and nearest neighbor aggregation techniques and comparisons were made on both image and pixel scales. Aggregation results illustrate that simple average with output flux aggregation provides close interpretation in aggregating fluxes to coarser resolution than other aggregation approaches. Pixel‐by‐pixel comparison using output aggregation with simple average resulted in close agreement (error range 5%–35%) between measured and up‐scaled fluxes, compared to input up‐scaling using simple average (error range 25%–60%). Larger error in input up‐scaling is due to the changes in the surface roughness parameters due to aggregation in SEBS model. In addition, the magnitude of errors in ETc estimation was observed to be a function of the heterogeneity of the land surface and evaporative elements over the study region. Comparison between up‐scaled ETc at 480 m spatial resolution with original MODIS image at 500 m showed that the output aggregation using simple average aggregation method provided closer representation of ETc at 500 m MODIS pixel resolution than the nearest neighbor resampling method.
      PubDate: 2016-03-11T06:36:20.623482-05:
      DOI: 10.1002/2015WR017772
       
  • Estimating groundwater dynamics at a Colorado River floodplain site using
           historical hydrological data and climate information
    • Authors: Jinsong Chen; Susan S. Hubbard, Kenneth H. Williams, Darren L. Ficklin
      Pages: 1881 - 1898
      Abstract: Long‐term prediction of groundwater dynamics is important for assessing water resources and their impacts on biogeochemical cycling. However, estimating future groundwater dynamics is challenging due to the wide range of spatiotemporal scales in hydrological processes and uncertainty in future climate conditions. In this study, we develop a Bayesian model to combine small‐scale historical hydrological data with large‐scale climate information to estimate groundwater dynamics at a floodplain site in Rifle, Colorado. Although we have only a few years of groundwater elevation measurements, we have 47 years of streamflow data from a gaging station approximately 43 km upstream and long‐term climate prediction on the Upper Colorado River Basin. To estimate future daily groundwater dynamics, we first develop a time series model to downscale the monthly streamflow derived from climate information to daily streamflow, and then transform the daily streamflow to groundwater dynamics at the downstream floodplain site. We use Monte Carlo methods to estimate future groundwater dynamics at the site through sampling from the joint posterior probability distribution. The results suggest that although future groundwater levels are expected to be similar to the current levels, the timing of the high groundwater levels is predicted to occur about 1 month earlier. The developed framework is extendable to other sites to estimate future groundwater dynamics given disparate data sets and climate projections. Additionally, the obtained estimates are being used as input to a site‐specific watershed reactive transport models to predict how climate‐induced changes will influence future biogeochemical cycling relevant to a variety of ecosystem services.
      PubDate: 2016-03-12T07:00:42.11297-05:0
      DOI: 10.1002/2015WR017777
       
  • Sampling variability in estimates of flow characteristics in
           coarse‐bed channels: Effects of sample size
    • Authors: Piotr Cienciala; Marwan A. Hassan
      Pages: 1899 - 1922
      Abstract: Adequate description of hydraulic variables based on a sample of field measurements is challenging in coarse‐bed streams, a consequence of high spatial heterogeneity in flow properties that arises due to the complexity of channel boundary. By applying a resampling procedure based on bootstrapping to an extensive field data set, we have estimated sampling variability and its relationship with sample size in relation to two common methods of representing flow characteristics, spatially averaged velocity profiles and fitted probability distributions. The coefficient of variation in bed shear stress and roughness length estimated from spatially averaged velocity profiles and in shape and scale parameters of gamma distribution fitted to local values of bed shear stress, velocity, and depth was high, reaching 15–20% of the parameter value even at the sample size of 100 (sampling density 1 m−2). We illustrated implications of these findings with two examples. First, sensitivity analysis of a 2‐D hydrodynamic model to changes in roughness length parameter showed that the sampling variability range observed in our resampling procedure resulted in substantially different frequency distributions and spatial patterns of modeled hydraulic variables. Second, using a bedload formula, we showed that propagation of uncertainty in the parameters of a gamma distribution used to model bed shear stress led to the coefficient of variation in predicted transport rates exceeding 50%. Overall, our findings underscore the importance of reporting the precision of estimated hydraulic parameters. When such estimates serve as input into models, uncertainty propagation should be explicitly accounted for by running ensemble simulations.
      PubDate: 2016-03-12T06:58:10.438081-05:
      DOI: 10.1002/2015WR017259
       
  • Spatiotemporal patterns of water table fluctuations and evapotranspiration
           induced by riparian vegetation in a semiarid area
    • Authors: Weifeng Yue; Tiejun Wang, Trenton E. Franz, Xunhong Chen
      Pages: 1948 - 1960
      Abstract: Groundwater evapotranspiration (ETg) links various ecohydrological processes and is an important component in regional water budgets. In this study, an extensive monitoring network was established in a semiarid riparian area to investigate various controls on the spatiotemporal pattern of water table fluctuations (WTFs) and ETg induced by riparian vegetation. Along a vegetation gradient (∼1200 m), diurnal WTFs were observed during a growing season in areas covered by woody species (Populus sect. Aigeiros and Juniperus virginiana) and wet slough vegetation (Panicum virgatum and Bromus inermis) with deeper root systems; whereas, no diurnal WTFs were found in the middle section with shallower‐rooted grasses (Poa pratensis and Carex sp.). The occurrence of diurnal WTFs was related to temperature‐controlled plant phenology at seasonal scales and to radiation at subdaily scales. Daily ETg in the mid‐growing season was calculated using the White method. The results revealed that depth to water table (DTWT) was the dominant control on ETg, followed by potential evapotranspiration (ETp). By combining the effects of DTWT and ETp, it was found that at shallower depths, ETg was more responsive to changes in ETp, due to the closer linkage of land surface processes with shallower groundwater. Finally, exponential relationships between ETg/ETp and DTWT were obtained at the study site, although those relationships varied considerably across the sites. This study demonstrates the complex interactions of WTFs and ETg with surrounding environmental variables and provides further insight into modeling ETg over different time scales and riparian vegetation.
      PubDate: 2016-03-12T06:56:22.293436-05:
      DOI: 10.1002/2015WR017546
       
  • Improving the theoretical underpinnings of process‐based hydrologic
           models
    • Authors: Martyn P. Clark; Bettina Schaefli, Stanislaus J. Schymanski, Luis Samaniego, Charles H. Luce, Bethanna M. Jackson, Jim E. Freer, Jeffrey R. Arnold, R. Dan Moore, Erkan Istanbulluoglu, Serena Ceola
      Pages: 2350 - 2365
      Abstract: In this Commentary, we argue that it is possible to improve the physical realism of hydrologic models by making better use of existing hydrologic theory. We address the following questions: (1) what are some key elements of current hydrologic theory; (2) how can those elements best be incorporated where they may be missing in current models; and (3) how can we evaluate competing hydrologic theories across scales and locations? We propose that hydrologic science would benefit from a model‐based community synthesis effort to reframe, integrate, and evaluate different explanations of hydrologic behavior, and provide a controlled avenue to find where understanding falls short.
      PubDate: 2016-03-11T06:34:55.884041-05:
      DOI: 10.1002/2015WR017910
       
  • Multiobjective adaptive surrogate modeling‐based optimization for
           parameter estimation of large, complex geophysical models
    • Authors: Wei Gong; Qingyun Duan, Jianduo Li, Chen Wang, Zhenhua Di, Aizhong Ye, Chiyuan Miao, Yongjiu Dai
      Abstract: Parameter specification is an important source of uncertainty in large, complex geophysical models. These models generally have multiple model outputs that require multi‐objective optimization algorithms. Although such algorithms have long been available, they usually require a large number of model runs and are therefore computationally expensive for large, complex dynamic models. In this paper, a multi‐objective adaptive surrogate modeling‐based optimization (MO‐ASMO) algorithm is introduced that aims to reduce computational cost while maintaining optimization effectiveness. Geophysical dynamic models usually have a prior parameterization scheme derived from the physical processes involved, and our goal is to improve all of the objectives by parameter calibration. In this study, we developed a method for directing the search processes towards the region that can improve all of the objectives simultaneously. We tested the MO‐ASMO algorithm against NSGA‐II and SUMO with 13 test functions and a land surface model ‐ the Common Land Model (CoLM). The results demonstrated the effectiveness and efficiency of MO‐ASMO. This article is protected by copyright. All rights reserved.
      PubDate: 2015-12-18T03:09:08.275785-05:
      DOI: 10.1002/2015WR018230
       
 
 
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