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        1 2     

  Subjects -> WATER RESOURCES (Total: 128 journals)
Acta Limnologica Brasiliensia     Open Access   (2 followers)
Advances in Oceanography and Limnology     Partially Free   (9 followers)
Advances in Water Resource and Protection     Open Access   (1 follower)
Advances in Water Resources     Hybrid Journal   (17 followers)
African Journal of Aquatic Science     Hybrid Journal   (13 followers)
Agricultural Water Management     Hybrid Journal   (13 followers)
American Water Works Association     Full-text available via subscription   (13 followers)
Anales de Hidrología Médica     Open Access  
Annals of Warsaw University of Life Sciences - SGGW. Land Reclamation     Open Access   (2 followers)
Annual Review of Marine Science     Full-text available via subscription   (9 followers)
Applied Water Science     Open Access   (5 followers)
Aquacultural Engineering     Hybrid Journal   (7 followers)
Aquaculture     Hybrid Journal   (26 followers)
Aquaculture Research     Hybrid Journal   (21 followers)
Aquatic Conservation Marine and Freshwater Ecosystems     Hybrid Journal   (19 followers)
Aquatic Geochemistry     Hybrid Journal   (1 follower)
Aquatic Living Resources     Hybrid Journal   (11 followers)
Aquatic Procedia     Open Access  
Aquatic Science and Technology     Open Access   (2 followers)
Aquatic Sciences     Hybrid Journal   (10 followers)
Asian Journal of Earth Sciences     Open Access   (16 followers)
Asian Journal of Rural Development     Open Access   (9 followers)
Australian Journal of Water Resources     Full-text available via subscription   (5 followers)
Bubble Science, Engineering & Technology     Hybrid Journal  
Canadian Water Resources Journal     Hybrid Journal   (17 followers)
Civil and Environmental Research     Open Access   (11 followers)
CLEAN - Soil, Air, Water     Hybrid Journal   (14 followers)
Computational Water, Energy, and Environmental Engineering     Open Access   (1 follower)
Continental Journal of Water, Air, and Soil Pollution     Open Access   (6 followers)
Cost Effectiveness and Resource Allocation     Open Access   (3 followers)
Desalination     Hybrid Journal   (9 followers)
Desalination and Water Treatment     Hybrid Journal   (8 followers)
Developments in Water Science     Full-text available via subscription   (6 followers)
Ecological Chemistry and Engineering S     Open Access   (2 followers)
Environmental Toxicology     Hybrid Journal   (8 followers)
EQA - International Journal of Environmental Quality     Open Access   (1 follower)
European journal of water quality - Journal européen d'hydrologie     Full-text available via subscription   (2 followers)
Ground Water Monitoring & Remediation     Hybrid Journal   (8 followers)
Grundwasser     Hybrid Journal  
Human Resources for Health     Open Access   (3 followers)
Hydro Nepal : Journal of Water, Energy and Environment     Open Access   (1 follower)
Hydrology Research     Partially Free   (6 followers)
International Journal of Climatology     Hybrid Journal   (10 followers)
International Journal of Hydrology Science and Technology     Hybrid Journal   (3 followers)
International Journal of Nuclear Desalination     Hybrid Journal   (2 followers)
International Journal of River Basin Management     Hybrid Journal   (1 follower)
International Journal of Salt Lake Research     Hybrid Journal   (2 followers)
International Journal of Waste Resources     Open Access   (3 followers)
International Journal of Water     Hybrid Journal   (10 followers)
International Journal of Water Resources and Environmental Engineering     Open Access  
International Journal of Water Resources Development     Hybrid Journal   (13 followers)
Iranian Journal of Environmental Health Science & Engineering     Open Access   (1 follower)
Irrigation and Drainage     Hybrid Journal   (3 followers)
Irrigation Science     Hybrid Journal   (3 followers)
Journal of Waste Water Treatment & Analysis     Open Access   (10 followers)
Journal of Aquatic Sciences     Full-text available via subscription  
Journal of Contemporary Water Resource & Education     Hybrid Journal   (2 followers)
Journal of Fisheries and Aquatic Science     Open Access   (4 followers)
Journal of Geophysical Research : Oceans     Partially Free   (14 followers)
Journal of Hydro-environment Research     Full-text available via subscription   (6 followers)
Journal of Hydroinformatics     Full-text available via subscription   (1 follower)
Journal of Hydrology (New Zealand)     Full-text available via subscription  
Journal of Hydrology and Hydromechanics     Open Access  
Journal of Hydrometeorology     Full-text available via subscription   (3 followers)
Journal of Limnology     Open Access   (6 followers)
Journal of the American Water Resources Association     Hybrid Journal   (18 followers)
Journal of Water and Climate Change     Partially Free   (22 followers)
Journal of Water and Health     Partially Free   (1 follower)
Journal of Water Chemistry and Technology     Hybrid Journal   (6 followers)
Journal of Water Resource and Hydraulic Engineering     Open Access   (3 followers)
Journal of Water Resource and Protection     Open Access   (5 followers)
Journal of Water Resources Planning and Management     Full-text available via subscription   (22 followers)
Journal of Water Reuse and Desalination     Partially Free   (6 followers)
Journal of Water Supply : Research and Technology - Aqua     Partially Free   (8 followers)
Journal of Water, Sanitation and Hygiene for Development     Open Access   (3 followers)
La Houille Blanche     Full-text available via subscription  
Lake and Reservoir Management     Hybrid Journal   (4 followers)
Lakes & Reservoirs Research & Management     Hybrid Journal   (15 followers)
Large Marine Ecosystems     Full-text available via subscription   (1 follower)
Mangroves and Salt Marshes     Hybrid Journal   (3 followers)
Marine and Freshwater Behaviour and Physiology     Hybrid Journal   (1 follower)
Methods in Oceanography : An International Journal     Hybrid Journal   (1 follower)
New Zealand Journal of Marine and Freshwater Research     Hybrid Journal   (4 followers)
Open Journal of Modern Hydrology     Open Access   (1 follower)
Osterreichische Wasser- und Abfallwirtschaft     Hybrid Journal  
Ozone Science & Engineering     Hybrid Journal   (1 follower)
Paddy and Water Environment     Hybrid Journal   (1 follower)
Research Journal of Environmental Toxicology     Open Access   (2 followers)
Reviews in Aquaculture     Hybrid Journal   (8 followers)
Revue des sciences de l'eau / Journal of Water Science     Full-text available via subscription   (1 follower)
Riparian Ecology and Conservation     Open Access   (3 followers)
River Research and Applications     Hybrid Journal   (5 followers)
River Systems     Full-text available via subscription   (3 followers)
SA Irrigation = SA Besproeiing     Full-text available via subscription  
San Francisco Estuary and Watershed Science     Open Access   (1 follower)
Sciences Eaux & Territoires : la Revue du Cemagref     Open Access   (1 follower)
Scientia Marina     Open Access   (2 followers)
Society & Natural Resources: An International Journal     Hybrid Journal   (9 followers)
Sri Lanka Journal of Aquatic Sciences     Open Access  
Sustainable Technologies, Systems & Policies     Open Access   (8 followers)

        1 2     

Water Resources Research    [87 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]   [SJR: 1.769]   [H-I: 110]
  • Modeling maximum daily temperature using a varying coefficient regression
    • Authors: Han Li; Xinwei Deng, Dong‐Yun Kim, Eric P. Smith
      Pages: n/a - n/a
      Abstract: Relationships between stream water and air temperatures are often modeled using linear or nonlinear regression methods. Despite a strong relationship between water and air temperatures and a variety of models that are effective for data summarized on a weekly basis, such models did not yield consistently good predictions for summaries such as daily maximum temperature. A good predictive model for daily maximum temperature is required because daily maximum temperature is an important measure for predicting survival of temperature sensitive fish. To appropriately model the strong relationship between water and air temperatures at a daily time step, it is important to incorporate information related to the time of the year into the modeling. In this work, a time varying coefficient model is used to study the relationship between air temperature and water temperature. The time varying coefficient model enables dynamic modeling of the relationship, and can be used to understand how the air‐water temperature relationship varies over time. The proposed model is applied to 10 streams in Maryland, West Virginia, Virginia, North Carolina and Georgia using daily maximum temperatures. It provides a better fit and better predictions than those produced by a simple linear regression model or a nonlinear logistic model.
      PubDate: 2014-03-22T02:06:35.940706-05:
      DOI: 10.1002/2013WR014243
  • Feedbacks between managed irrigation and water availability: Diagnosing
           temporal and spatial patterns using an integrated hydrologic model
    • Authors: Laura E. Condon; Reed M. Maxwell
      Pages: n/a - n/a
      Abstract: Groundwater‐fed irrigation has been shown to deplete groundwater storage, decrease surface water runoff, and increase evapotranspiration. Here we simulate soil moisture‐dependent groundwater‐fed irrigation with an integrated hydrologic model. This allows for direct consideration of feedbacks between irrigation demand and groundwater depth. Special attention is paid to system dynamics in order to characterized spatial variability in irrigation demand and response to increased irrigation stress. A total of 80 years of simulation are completed for the Little Washita Basin in Southwestern Oklahoma, USA spanning a range of agricultural development scenarios and management practices. Results show regionally aggregated irrigation impacts consistent with other studies. However, here a spectral analysis reveals that groundwater‐fed irrigation also amplifies the annual streamflow cycle while dampening longer‐term cyclical behavior with increased irrigation during climatological dry periods. Feedbacks between the managed and natural system are clearly observed with respect to both irrigation demand and utilization when water table depths are within a critical range. Although the model domain is heterogeneous with respect to both surface and subsurface parameters, relationships between irrigation demand, water table depth, and irrigation utilization are consistent across space and between scenarios. Still, significant local heterogeneities are observed both with respect to transient behavior and response to stress. Spatial analysis of transient behavior shows that farms with groundwater depths within a critical depth range are most sensitive to management changes. Differences in behavior highlight the importance of groundwater's role in system dynamics in addition to water availability.
      PubDate: 2014-03-21T11:34:01.212538-05:
      DOI: 10.1002/2013WR014868
  • Characterization of groundwater and surface water mixing in a semiconfined
           karst aquifer using time‐lapse electrical resistivity tomography
    • Authors: Steven B. Meyerhoff; Reed M. Maxwell, André Revil, Jonathan B. Martin, Marios Karaoulis, Wendy D. Graham
      Pages: n/a - n/a
      Abstract: Groundwater flow in karst includes exchange of water between large fractures, conduits, and the surrounding porous matrix, which impacts both water quality and quantity. Electrical resistivity tomography combined with end‐member mixing analysis (EMMA) and numerical flow and transport modeling was used to study mixing of karst conduit and matrix waters to understand spatial and temporal patterns of mixing during high flow and base flow conditions. To our knowledge, this is the first time EMMA and synthetic geophysical simulations have been combined. Here we interpret an 8 week time‐lapse electrical resistivity data set to assess groundwater‐surface mixing. We simulate flow between the karst conduits and the porous matrix to determine fractions of water recharged to conduits that has mixed with groundwater stored in the pore space of the matrix using a flow and transport model in a synthetic time‐lapse resistivity inversion. Comparing the field and synthetic inversions, our results enable us to estimate exchange dynamics, spatial mixing, and flow conditions. Results showed that mixing occurred at a volumetric flux of 56 m3/d with a dispersivity around 1.69 m during the geophysical experiment. For these conditions, it was determined that conduit water composition ranged from 75% groundwater during base flow conditions to less than 50% groundwater in high flow conditions. Though subject to some uncertainties, the time‐lapse inversion process provides a means to predict changing hydrologic conditions, leading to mixing of surface water and ground water and thus changes to water quantity and quality, as well as potential for water‐rock reactions, in a semiconfined, sink‐rise system.
      PubDate: 2014-03-21T11:33:59.087196-05:
      DOI: 10.1002/2013WR013991
  • Assessing mechanical vulnerability in water distribution networks under
           multiple failures
    • Authors: Luigi Berardi; Rita Ugarelli, Jon Røstum, Orazio Giustolisi
      Pages: n/a - n/a
      Abstract: Understanding mechanical vulnerability of water distribution networks (WDN) is of direct relevance for water utilities since it entails two different purposes. On the one hand, it might support the identification of severe failure scenarios due to external causes (e.g., natural or intentional events) which result into the most critical consequences on WDN supply capacity. On the other hand, it aims at figure out the WDN portions which are more prone to be affected by asset disruptions. The complexity of such analysis stems from the number of possible scenarios with single and multiple simultaneous shutdowns of asset elements leading to modifications of network topology and insufficient water supply to customers. In this work, the search for the most disruptive combinations of multiple asset failure events is formulated and solved as a multiobjective optimization problem. The higher vulnerability failure scenarios are detected as those causing the lower supplied demand due to the lower number of simultaneous failures. The automatic detection of WDN topology, subsequent to the detachments of failed elements, is combined with pressure‐driven analysis. The methodology is demonstrated on a real water distribution network. Results show that, besides the failures causing the detachment of reservoirs, tanks, or pumps, there are other different topological modifications which may cause severe WDN service disruptions. Such information is of direct relevance to support planning asset enhancement works and improve the preparedness to extreme events.
      PubDate: 2014-03-21T10:16:12.239806-05:
      DOI: 10.1002/2013WR014770
  • Predictability of tracer dilution in large open channel flows: Analytical
           solution for the coefficient of variation of the depth‐averaged
    • Authors: Marilena Pannone
      Pages: n/a - n/a
      Abstract: A large‐time analytical solution is proposed for the spatial variance and coefficient of variation of the depth‐averaged concentration due to instantaneous, cross sectionally uniform solute sources in pseudorectangular open channel flows. The mathematical approach is based on the use of the Green functions and on the Fourier decomposition of the depth‐averaged velocities, coupled with the method of the images. The variance spatial trend is characterized by a minimum at the center of the mass and two mobile, decaying symmetrical peaks which, at very large times, are located at the inflexion points of the average Gaussian distribution. The coefficient of variation, which provides an estimate of the expected percentage deviation of the depth‐averaged point concentrations about the section‐average, exhibits a minimum at the center which decays like t−1 and only depends on the river diffusive time scale. The defect of cross‐sectional mixing quickly increases with the distance from the center, and almost linearly at large times. Accurate numerical Lagrangian simulations were performed to validate the analytical results in preasymptotic and asymptotic conditions, referring to a particularly representative sample case for which cross‐sectional depth and velocity measurements were known from a field survey. In addition, in order to discuss the practical usefulness of computing large‐time concentration spatial moments in river flows, and resorting to directly measured input data, the order of magnitude of section‐averaged concentrations and corresponding coefficients of variation was estimated in field conditions and for hypothetical contamination scenarios, considering a unit normalized mass impulsively injected across the transverse section of 81 U.S. rivers.
      PubDate: 2014-03-21T08:22:18.796891-05:
      DOI: 10.1002/2013WR013986
  • Reply to comment by Chu et al. on “High‐dimensional posterior
           exploration of hydrologic models using multiple‐try DREAM (ZS) and
           high‐performance computing”
    • Authors: Jasper A. Vrugt; Eric Laloy
      Pages: n/a - n/a
      PubDate: 2014-03-21T08:20:28.238966-05:
      DOI: 10.1002/2013WR014425
  • Comment on “High‐dimensional posterior exploration of
           hydrologic models using multiple‐try DREAM (ZS) and
    • Authors: Wei Chu; Tiantian Yang, Xiaogang Gao
      Pages: n/a - n/a
      PubDate: 2014-03-21T08:19:32.06798-05:0
      DOI: 10.1002/2012WR013341
  • Assessing variability of evapotranspiration over the Ganga river basin
           using water balance computations
    • Authors: Tajdarul H. Syed; Peter J. Webster, James S. Famiglietti
      Pages: n/a - n/a
      Abstract: A thorough assessment of evapotranspiration (ET) pervades several important issues of the 21st century including climate change, food‐security, land‐management, flood and drought prediction, and water resources assessment and management. Such a proper assessment is of particular importance in the Ganga river basin (GRB) with its backdrop of a rapidly increasing population pressure and unregulated use of water resources. Spatially averaged ET over the GRB is computed as the residual of atmospheric and terrestrial water budget computations using a combination of model simulations and satellite and ground‐based observations. The best estimate of monthly ET is obtained as the monthly mean of atmospheric and terrestrial water balance computations for the period 1980–2007. The mean monthly average of ET from these various estimates is 72.3 ± 18.8 mm month−1. Monthly variations of ET peak between July and August and reach a minimum in February. For the entire study period, the rate of change of ET across the GRB is −11 mm yr−2 (i.e., mm/yr/yr). Alongside a notable influence of the 1997–1998 El Niño, results allude to the existence of interim periods during which ET trends varied significantly. More specifically, during the period of 1998–2002, the rate of decline increased to −55.8 mm yr−2, which is almost 5 times the overall trend. Based on the correlation between ET and independent estimates of near‐surface temperature and soil moisture, we can infer that the ET over the GRB is primarily limited by moisture availability. The analysis has important potential for use in large‐scale water budget assessments and intercomparison studies. The analysis also emphasizes the importance of synergistic use of mutliplatform hydrologic information.
      PubDate: 2014-03-21T08:19:30.075117-05:
      DOI: 10.1002/2013WR013518
  • Simulation of earth textures by conditional image quilting
    • Authors: K. Mahmud; G. Mariethoz, J. Caers, P. Tahmasebi, A. Baker
      Pages: n/a - n/a
      Abstract: Training image‐based approaches for stochastic simulations have recently gained attention in surface and subsurface hydrology. This family of methods allows the creation of multiple realizations of a study domain, with a spatial continuity based on a training image (TI) that contains the variability, connectivity, and structural properties deemed realistic. A major drawback of these methods is their computational and/or memory cost, making certain applications challenging. It was found that similar methods, also based on training images or exemplars, have been proposed in computer graphics. One such method, Image Quilting (IQ), is introduced in this paper and adapted for hydrogeological applications. The main difficulty is that Image Quilting was originally not designed to produce conditional simulations and was restricted to 2D images. In this paper, the original method developed in computer graphics has been modified to accommodate conditioning data and 3D problems. This new Conditional Image Quilting method (CIQ) is patch‐based, does not require constructing a pattern databases, and can be used with both categorical and continuous training images. The main concept is to optimally cut the patches such that they overlap with minimum discontinuity. The optimal cut is determined using a dynamic programming algorithm. Conditioning is accomplished by prior selection of patches that are compatible with the conditioning data. The performance of CIQ is tested for a variety of hydrogeological test cases. The results, when compared with previous Multiple‐point Statistics (MPS) methods, indicate an improvement in CPU time by a factor of at least 50.
      PubDate: 2014-03-21T04:13:05.379528-05:
      DOI: 10.1002/2013WR015069
  • A streamline splitting pore‐network approach for computationally
           inexpensive and accurate simulation of transport in porous media
    • Authors: Yashar Mehmani; Mart Oostrom, Matthew T. Balhoff
      Pages: n/a - n/a
      Abstract: Several approaches have been developed in the literature for solving flow and transport at the pore scale. Some authors use a direct modeling approach where the fundamental flow and transport equations are solved on the actual pore‐space geometry. Such direct modeling, while very accurate, comes at a great computational cost. Network models are computationally more efficient because the pore‐space morphology is approximated. Typically, a mixed cell method (MCM) is employed for solving the flow and transport system which assumes pore‐level perfect mixing. This assumption is invalid at moderate to high Peclet regimes. In this work, a novel Eulerian perspective on modeling flow and transport at the pore scale is developed. The new streamline splitting method (SSM) allows for circumventing the pore‐level perfect‐mixing assumption, while maintaining the computational efficiency of pore‐network models. SSM was verified with direct simulations and validated against micromodel experiments; excellent matches were obtained across a wide range of pore‐structure and fluid‐flow parameters. The increase in the computational cost from MCM to SSM is shown to be minimal, while the accuracy of SSM is much higher than that of MCM and comparable to direct modeling approaches. Therefore, SSM can be regarded as an appropriate balance between incorporating detailed physics and controlling computational cost. The truly predictive capability of the model allows for the study of pore‐level interactions of fluid flow and transport in different porous materials. In this paper, we apply SSM and MCM to study the effects of pore‐level mixing on transverse dispersion in 3‐D disordered granular media.
      PubDate: 2014-03-20T13:29:42.164715-05:
      DOI: 10.1002/2013WR014984
  • Probabilistic prediction of cyanobacteria abundance in a Korean reservoir
           using a Bayesian Poisson model
    • Authors: YoonKyung Cha; Seok Soon Park, Kyunghyun Kim, Myeongseop Byeon, Craig A. Stow
      Pages: n/a - n/a
      Abstract: There have been increasing reports of harmful algal blooms (HABs) worldwide. However, the factors that influence cyanobacteria dominance and HAB formation can be site‐specific and idiosyncratic, making prediction challenging. The drivers of cyanobacteria blooms in Lake Paldang, South Korea, the summer climate of which is strongly affected by the East Asian monsoon, may differ from those in well‐studied North American lakes. Using the observational data sampled during the growing season in 2007–2011, a Bayesian hurdle Poisson model was developed to predict cyanobacteria abundance in the lake. The model allowed cyanobacteria absence (zero count) and nonzero cyanobacteria counts to be modeled as functions of different environmental factors. The model predictions demonstrated that the principal factor that determines the success of cyanobacteria was temperature. Combined with high temperature, increased residence time indicated by low outflow rates appeared to increase the probability of cyanobacteria occurrence. A stable water column, represented by low suspended solids, and high temperature were the requirements for high abundance of cyanobacteria. Our model results had management implications; the model can be used to forecast cyanobacteria watch or alert levels probabilistically and develop mitigation strategies of cyanobacteria blooms.
      PubDate: 2014-03-20T13:29:29.525561-05:
      DOI: 10.1002/2013WR014372
  • Potential of a low‐cost sensor network to understand the spatial and
           temporal dynamics of a mountain snow cover
    • Authors: Stefan Pohl; Jakob Garvelmann, Jens Wawerla, Markus Weiler
      Pages: n/a - n/a
      Abstract: The spatial and temporal dynamics of seasonal snow covers play a critical role for many hydrological, ecological, and climatic processes. This paper presents a new, innovative approach to continuously monitor these dynamics using numerous low‐cost, standalone snow monitoring stations (SnoMoS). These stations provide snow and related meteorological data with a high temporal and spatial resolution. Data collected by SnoMoS include: snow depth, surface temperature, air temperature and humidity, total precipitation, global radiation, wind speed, and barometric pressure. A total of 99 sensors were placed over the winters 2010/2011 and 2011/2012 at multiple locations within three 40–180 km2 basins in the Black Forest region of Southern Germany. The locations were chosen to cover a wide range of slopes, elevations, and expositions in a stratified sampling design. Furthermore, “paired stations” located in close proximity to each other, one in the open and one underneath various forest canopies, were set up to investigate the influence of vegetation on snow dynamics. The results showed that considerable differences in snow depth and, therefore, snow water equivalent (SWE) are present within the study area despite its moderate temperatures and medium elevation range (400–1500 m). The relative impact of topographical factors like elevation, aspect, and of different types of forest vegetation were quantified continuously and were found to change considerably over the winter period. The recorded differences in SWE and snow cover duration were large enough that they should be considered in hydrologic and climate models.
      PubDate: 2014-03-20T13:29:27.049985-05:
      DOI: 10.1002/2013WR014594
  • Internal variability and model uncertainty components in future
           hydrometeorological projections: The Alpine Durance basin
    • Authors: M. Lafaysse; B. Hingray, A. Mezghani, J. Gailhard, L. Terray
      Pages: n/a - n/a
      Abstract: A multireplicate multimodel ensemble of hydrological simulations covering the 1860‐2099 period has been produced for the Upper Durance River basin (French Alps). An original quasi‐ergodic analysis of variance was applied to quantify uncertainties related to General Circulation Models (GCMs), Statistical Downscaling Models (SDMs) and the internal variability of each GCM/SDM simulation chain. For temperature, GCM uncertainty prevails and SDM uncertainty is non‐negligible. Significant warming and in turn significant changes are predicted for evaporation, snow cover and seasonality of discharges. For precipitation, GCM and SDM uncertainty components are of the same order. A high contribution of the large and small scale components of internal variability is also obtained, inherited respectively from the GCMs and the different replicates of a given SDM. The same applies for annual discharge. The uncertainty in values that could be experienced for any given future period is therefore very high. For both discharge and precipitation, even the sign of future realizations is uncertain at a 90% confidence level.These findings have important implications. Similarly to GCM uncertainty, SDM uncertainty cannot be neglected. The same applies for both components of internal variability. Climate change impact studies based on a single SDM realization are likely to be no more relevant than those based on a single GCM run. They may lead to poor decisions for climate change adaptation.
      PubDate: 2014-03-20T05:15:08.988122-05:
      DOI: 10.1002/2013WR014897
  • Root‐zone soil moisture estimation using data‐driven methods
    • Authors: Kurt C. Kornelsen; Paulin Coulibaly
      Pages: n/a - n/a
      Abstract: The soil moisture state partitions both mass and energy fluxes and is important for many hydrogeochemical cycles, but is often only measured within the surface layer. Estimating the amount of soil moisture in the root‐zone from this information is difficult due to the non‐linear and heterogeneous nature of the various processes which alter the soil moisture state. Data‐driven methods, such as artificial neural networks (ANN), mine data for non‐linear interdependencies and have potential for estimating root‐zone soil moisture from surface soil moisture observations. To create an ANN root‐zone model that was non‐site specific and physically constrained, a training set was generated by forcing HYDRUS‐1D with meteorological observations for different soil profiles from the UNSODA database. Ensemble ANNs were trained to provide soil moisture at depths of 10, 20 and 50 cm below the surface using surface soil moisture observations and local meteorological information. Insights into the processes represented by the ANNs were derived from a clamping sensitivity analysis and by changing the ANNs input data. Further model testing based on synthetic soil moisture profiles from three McMaster Mesonet and three USDA SCAN sites suggests that ANNs are a flexible tool capable of predicting root‐zone soil moisture with good accuracy. It was found that ANNs could well represent soil moisture as estimated by HYDRUS‐1D, but performance was reduced in comparison to in situ soil moisture observations outside the training conditions. The transferability of the model appears limited to the same geographic region.
      PubDate: 2014-03-20T04:39:42.627812-05:
      DOI: 10.1002/2013WR014127
  • A modeling approach reveals differences in evapotranspiration and its
           partitioning in two semiarid ecosystems in northwest Mexico
    • Authors: Luis A. Méndez‐Barroso; Enrique R. Vivoni, Agustin Robles‐Morua, Giuseppe Mascaro, Enrico A. Yépez, Julio C. Rodríguez, Christopher J. Watts, Jaime Garatuza‐Payán, Juan A. Saíz‐Hernández
      Pages: n/a - n/a
      Abstract: Seasonal vegetation changes during the North American monsoon play a major role in modifying water, energy and momentum fluxes. Nevertheless, most models parameterize plants as a static component or with averaged seasonal variations that ignore interannual differences and their potential impact on evapotranspiration (ET) and its components. Here, vegetation parameters derived from remote sensing data were coupled with a hydrologic model at two eddy covariance (EC) sites with observations spanning multiple summers. Sinaloan thornscrub (ST) and Madrean woodland (MW) sites, arranged at intermediate and high elevations along mountain fronts in northwest Mexico, occupy specific niches related to climate conditions and water availability that are poorly understood. We found that simulations with a dynamic representation of vegetation greening tracked well the seasonal evolution of observed ET and soil moisture (SM). A switch in the dominant component of ET from soil evaporation (E) to plant transpiration (T) was observed for each ecosystem depending on the timing and magnitude of vegetation greening that is directly tied to rainfall characteristics. Differences in vegetation greening at the ST and MW sites lead to a dominance of transpiration at ST (T/ET = 57%), but evaporation‐dominant conditions at MW (T/ET = 19%). Peak transpiration occurred at five and twenty days after the full canopy development in the ST and MW sites, respectively. These results indicate that evapotranspiration timing and partitioning varies considerably in the two studied ecosystems in accordance with different modes of vegetation greening. Intermediate‐elevation ecosystems follow an intensive water use strategy with a rapid and robust transpiration response to water availability. In contrast, higher elevation sites have delayed and attenuated transpiration, suggesting an extensive water use strategy persisting beyond the North American monsoon.
      PubDate: 2014-03-20T04:39:40.698995-05:
      DOI: 10.1002/2013WR014838
  • Cauchy data requirement of the inverse problem of the mean age equation
    • Authors: Mohamed K. Nassar; Timothy R. Ginn
      Pages: n/a - n/a
      Abstract: A classical theoretical inverse problem in groundwater hydraulics is the calibration of a heterogeneous isotropic hydraulic conductivity field using known hydraulic head data at each point in the domain. It has been long known that a necessary condition for the uniqueness of the solution to this theoretical inverse problem is the Cauchy data, i.e., the hydraulic conductivity values (or, equivalently, flux) along a line crossing all streamtubes in the entire domain. This result has been cited in identifying the value of boundary flux data in practical inverse problems, although in general such data are generally not available. In this work, we show that groundwater mean age data replaces this Cauchy data requirement.
      PubDate: 2014-03-20T04:39:36.543557-05:
      DOI: 10.1002/2013WR014674
  • Decadal surface water quality trends under variable climate, land use, and
           hydrogeochemical setting in Iowa, USA
    • Authors: Christopher T. Green; Barbara A. Bekins, Stephen J. Kalkhoff, Robert M. Hirsch, Lixia Liao, Kimberlee K. Barnes
      Pages: n/a - n/a
      Abstract: Understanding how nitrogen fluxes respond to changes in agriculture and climate is important for improving water quality. In the midwestern United States, expansion of corn cropping for ethanol production led to increasing N application rates in the 2000s during a period of extreme variability of annual precipitation. To examine the effects of these changes, surface water quality was analyzed in 10 major Iowa Rivers. Several decades of concentration and flow data were analyzed with a statistical method that provides internally consistent estimates of the concentration history and reveals flow‐normalized trends that are independent of year‐to‐year streamflow variations. Flow‐normalized concentrations of nitrate+nitrite‐N decreased from 2000 to 2012 in all basins. To evaluate effects of annual discharge and N loading on these trends, multiple conceptual models were developed and calibrated to flow‐weighted annual concentrations. The recent declining concentration trends can be attributed to both very high and very low discharge in the 2000s and to the long (e.g., 8 year) subsurface residence times in some basins. Dilution of N and depletion of stored N occurs in years with high discharge. Reduced N transport and increased N storage occurs in low‐discharge years. Central Iowa basins showed the greatest reduction in flow‐normalized concentrations, likely because of smaller storage volumes and shorter residence times. Effects of land‐use changes on the water quality of major Iowa Rivers may not be noticeable for years or decades in peripheral basins of Iowa, and may be obscured in the central basins where extreme flows strongly affect annual concentration trends.
      PubDate: 2014-03-19T14:31:07.44154-05:0
      DOI: 10.1002/2013WR014829
  • Theory of transient streaming potentials in coupled unconfined
           aquifer‐unsaturated zone flow to a well
    • Authors: Bwalya Malama
      Pages: n/a - n/a
      Abstract: A semi‐analytical solution is presented for transient streaming potentials associated with flow to a pumping well in an unconfined aquifer, taking into account the effect of flow in the unsaturated zone above the water table. Flow in the unsaturated zone is modeled with a linearized form of Richards' equation using an exponential model for soil moisture retention and unsaturated hydraulic conductivity. Archie's law is invoked for unsaturated electrical conductivity. The unsaturated electrokinetic coupling coefficient is modeled with a decaying exponential, where the maximum value is at and below the water table. The coupled flow and electrokinetic problem is solved using Laplace and Hankel transforms. The results of the model predicted behavior are presented and compared to that observed in laboratory simulations of pumping tests. The early‐time polarity reversal predicted the model is observable in the experiments. Other non‐monotonic streaming potential behaviors predicted by the model are also evident in experimental measurements. The model is used to estimate hydraulic parameters from SP data and these compare well to those obtained from drawdown data. For example, a hydraulic conductivity of 3.6 × 10‐4 m/s is obtained from SP data compared to 3.4 × 10‐4 m/s from drawdown data.
      PubDate: 2014-03-19T12:30:39.648499-05:
      DOI: 10.1002/2013WR014909
  • Exploring the link between meteorological drought and streamflow: Effects
           of climate‐catchment interaction
    • Authors: Klaus Haslinger; Daniel Koffler, Wolfgang Schöner, Gregor Laaha
      Pages: n/a - n/a
      Abstract: In this paper, we perform a detailed regional analysis of the link between meteorological drought indices and streamflow for a comprehensive Austrian data set of 47 small to medium‐size catchments in humid‐temperate climate. Four drought indices considering different components of the catchment water balance are tested. We assess the quality of the link using rank correlation analysis, and the probability of detecting low‐flow events by hit‐scores. Overall, correlations range between 0.4 and 0.8 and differ significantly between regions. A stratified analysis shows that the link is much stronger (i) for summer low flows and droughts than for anomalies in general, and (ii) for more humid than more arid conditions. Under more humid conditions streamflow droughts of small to medium‐size catchments are to a large extent generated by climate forcing and therefore well represented by a simple meteorological index. Under increasingly dry conditions, the climate signal gets less predictive, and storage properties of the underground become more important. A simple soil moisture accounting scheme (such as those of the Palmer index) can considerably improve the correlations. Overall, we conclude there is a significant link between meteorological drought and streamflow drought, except for catchments where groundwater storage and snow processes are important. The results are encouraging and provide a wealth of information which can profitably be used to set up statistical prediction models to estimate low flows from meteorological time series.
      PubDate: 2014-03-19T12:27:24.983646-05:
      DOI: 10.1002/2013WR015051
  • Constraining a compositional flow model with flow‐chemical data
           using an ensemble‐based Kalman filter
    • Authors: M. E. Gharamti; A. Kadoura, J. Valstar, S. Sun, I. Hoteit
      Pages: n/a - n/a
      Abstract: Isothermal compositional flow models require coupling transient compressible flows and advective transport systems of various chemical species in subsurface porous media. Building such numerical models is quite challenging and may be subject to many sources of uncertainties because of possible incomplete representation of some geological parameters that characterize the system's processes. Advanced data assimilation methods, such as the ensemble Kalman filter (EnKF), can be used to calibrate these models by incorporating available data. In this work, we consider the problem of estimating reservoir permeability using information about phase pressure as well as the chemical properties of fluid components. We carry out state‐parameter estimation experiments using joint and dual updating schemes in the context of the EnKF with a two‐dimensional single‐phase compositional flow model (CFM). Quantitative and statistical analyses are performed to evaluate and compare the performance of the assimilation schemes. Our results indicate that including chemical composition data significantly enhances the accuracy of the permeability estimates. In addition, composition data provide more information to estimate system states and parameters than do standard pressure data. The dual state‐parameter estimation scheme provides about 10% more accurate permeability estimates on average than the joint scheme when implemented with the same ensemble members, at the cost of twice more forward model integrations. At similar computational cost, the dual approach becomes only beneficial after using large enough ensembles.
      PubDate: 2014-03-19T11:32:09.519375-05:
      DOI: 10.1002/2013WR014830
  • Straight thinking about groundwater recession
    • Authors: M. O. Cuthbert
      Pages: n/a - n/a
      Abstract: While in catchment and hillslope hydrology a more nuanced approach is now taken to streamflow recession analysis, in the context of major aquifers it is commonly still assumed that the groundwater head recession rate will take exponential form, an idea originally proposed in the 19th Century. However it is shown here that, in early times, the groundwater head recession in a major aquifer should take an almost straight line form with a rate approximately equal to the long‐term recharge rate divided by the aquifer storage coefficient. The length of this phase can be estimated from an analytical expression derived in the paper which depends on the aquifer diffusivity, length scale, and the position of the monitoring point. A transitional phase then leads to an exponential phase after some critical time which is independent of the position of the monitoring point. Major aquifers in a state of periodic quasi‐steady state are expected to have rates of groundwater flux recession which deviate little from the average rate of groundwater recharge. Where quasi‐exponential groundwater declines are observed in nature, their form may be diagnostic of particular types of aquifer properties and/or boundary effects, such as proximity to drainage boundaries, variations in transmissivity with hydraulic head, storage changes due to pumping, nonequilibrium flow at a range of spatial and temporal scales, and variations in specific yield with depth. Recession analysis has applicability to a range of groundwater problems and is powerful way of gaining insight into the hydrologic functioning of an aquifer.
      PubDate: 2014-03-19T08:41:24.956019-05:
      DOI: 10.1002/2013WR014060
  • Salinity effects on cracking morphology and dynamics in 3‐D
           desiccating clays
    • Authors: Keita F. DeCarlo; Nima Shokri
      Pages: n/a - n/a
      Abstract: Saline conditions induce not only chemical but physical changes in swelling clays, and have a significant influence on the crack dynamics and morphology of desiccating clays. In this study, we used X‐ray micro‐tomography to experimentally investigate the effects of sodium chloride on the morphology and dynamics of desiccation cracks in three‐dimensional mixtures of sand‐bentonite slurry under varying rheological conditions. Rectangular glass containers were packed with slurries of different salt concentrations, with the top boundary exposed to air for evaporation. The growth and propagation of the cracking network that subsequently formed was visualized in 3D at multiple intervals. The characterization of cracking and branching behavior shows a high extent of localized surficial crack networks at low salinity, with a transition to less extensive but more centralize crack networks with increased salinity. The observed behavior was described in the context of the physicochemical properties of the montmorillonite clay, where shifts from an “entangled” (large platelet spacing, small pore structure) to a “stacked” (small platelet spacing, open pore structure) network influence fluid distribution and thus extent of cracking and branching behavior. This is further corroborated by vertical profiles of water distribution, which shows localized desiccation fronts that shift to uniform desaturation with increasing salt concentration. Our results provide new insights regarding the formation, dynamics, and patterns of desiccation cracks formed during evaporation from 3D saline clay structures, which will be useful in hydrological applications including water management, land surface evaporation, and subsurface contaminant transport.
      PubDate: 2014-03-19T08:34:29.335495-05:
      DOI: 10.1002/2013WR014424
  • On modeling the paleohydrologic response of closed‐basin lakes to
           fluctuations in climate: Methods, applications, and implications
    • Authors: Ganming Liu; Franklin W. Schwartz
      Pages: n/a - n/a
      Abstract: Climate reconstructions using tree rings and lake sediments have contributed significantly to the understanding of Holocene climates. Approaches focused specifically on reconstructing the temporal water‐level response of lakes, however, are much less developed. This paper describes a statistical correlation approach based on time series with Palmer Drought Severity Index (PDSI) values derived from instrumental records or tree rings as a basis for reconstructing stage hydrographs for closed‐basin lakes. We use a distributed lag correlation model to calculate a variable, ωt that represents the water level of a lake at any time t as a result of integrated climatic forcing from preceding years. The method was validated using both synthetic and measured lake‐stage data and the study found that a lake's “memory” of climate fades as time passes, following an exponential‐decay function at rates determined by the correlation time lag. Calculated trends in ωt for Moon Lake, Rice Lake, and Lake Mina from AD 1401 to 1860 compared well with the established chronologies (salinity, moisture, and Mg/Ca ratios) reconstructed from sediments. This method provides an independent approach for developing high‐resolution information on lake behaviors in pre‐instrumental times and has been able to identify problems of climate signal deterioration in sediment‐based climate reconstructions in lakes with a long time lag.
      PubDate: 2014-03-19T04:38:30.836373-05:
      DOI: 10.1002/2013WR014107
  • Carbon storage in mountainous headwater streams: The role of
           old‐growth forest and logjams
    • Authors: Natalie D. Beckman; Ellen Wohl
      Pages: n/a - n/a
      Abstract: We measured wood piece characteristics and particulate organic matter (POM) in stored sediments in 30 channel‐spanning logjams along headwater streams in the Colorado Front Range, USA. Logjams are on streams flowing through old‐growth (>200 years), disturbed (
      PubDate: 2014-03-18T13:08:46.512979-05:
      DOI: 10.1002/2013WR014167
  • Is the Dupuit assumption suitable for predicting the groundwater seepage
           area in hillslopes?
    • Authors: E. Bresciani; P. Davy, J.‐R. de Dreuzy
      Pages: n/a - n/a
      Abstract: Many physically based hydrological/hydrogeological models used for predicting groundwater seepage areas, including topography‐based index models such as TOPMODEL, rely on the Dupuit assumption. To ensure the sound use of these simplified models, knowledge of the conditions under which they provide a reasonable approximation is critical. In this study, a Dupuit solution for the seepage length in hillslope cross sections is tested against a full‐depth solution of saturated groundwater flow. In homogeneous hillslopes with horizontal impervious base and constant‐slope topography, the comparison reveals that the validity of the Dupuit solution depends not only on the ratio of depth to hillslope length d/L (as might be expected), but also on the ratio of hydraulic conductivity to recharge K/R and on the topographic slope s. The validity of the Dupuit solution is shown to be in fact a unique function of another ratio, the ratio of depth to seepage length d/LS. For d/LS 
      PubDate: 2014-03-18T11:20:02.97707-05:0
      DOI: 10.1002/2013WR014284
  • Comparison of joint versus postprocessor approaches for hydrological
           uncertainty estimation accounting for error autocorrelation and
    • Authors: Guillaume Evin; Mark Thyer, Dmitri Kavetski, David McInerney, George Kuczera
      Pages: n/a - n/a
      Abstract: The paper appraises two approaches for the treatment of heteroscedasticity and autocorrelation in residual errors of hydrological models. Both approaches use weighted least squares (WLS), with heteroscedasticity modeled as a linear function of predicted flows and autocorrelation represented using an AR(1) process. In the first approach, heteroscedasticity and autocorrelation parameters are inferred jointly with hydrological model parameters. The second approach is a two‐stage “postprocessor” scheme, where Stage 1 infers the hydrological parameters ignoring autocorrelation and Stage 2 conditionally infers the heteroscedasticity and autocorrelation parameters. These approaches are compared to a WLS scheme that ignores autocorrelation. Empirical analysis is carried out using daily data from 12 US catchments from the MOPEX set using two conceptual rainfall‐runoff models, GR4J, and HBV. Under synthetic conditions, the postprocessor and joint approaches provide similar predictive performance, though the postprocessor approach tends to underestimate parameter uncertainty. However, the MOPEX results indicate that the joint approach can be nonrobust. In particular, when applied to GR4J, it often produces poor predictions due to strong multiway interactions between a hydrological water balance parameter and the error model parameters. The postprocessor approach is more robust precisely because it ignores these interactions. Practical benefits of accounting for error autocorrelation are demonstrated by analyzing streamflow predictions aggregated to a monthly scale (where ignoring daily‐scale error autocorrelation leads to significantly underestimated predictive uncertainty), and by analyzing one‐day‐ahead predictions (where accounting for the error autocorrelation produces clearly higher precision and better tracking of observed data). Including autocorrelation into the residual error model also significantly affects calibrated parameter values and uncertainty estimates. The paper concludes with a summary of outstanding challenges in residual error modeling, particularly in ephemeral catchments.
      PubDate: 2014-03-18T11:12:27.892616-05:
      DOI: 10.1002/2013WR014185
  • Stochastic simulation of intermittent rainfall using the concept of
           “dry drift”
    • Authors: Marc Schleiss; Sabine Chamoun, Alexis Berne
      Pages: n/a - n/a
      Abstract: A stochastic rainfall simulator based on the concept of “dry drift” is proposed. It is characterized by a new and nonstationary representation of rainfall in which the average rain rate (in log‐space) depends on the distance to the closest surrounding dry areas. The result is a more realistic transition between dry and rainy areas and a better distribution of low and high rain rates inside the simulated rainy areas. The proposed approach is very general and can be used to simulate both unconditional and conditional rain rate time series, two‐dimensional fields, and space‐time fields. The parameterization is intuitive and can be done using time series and/or radar rain‐rate maps. Several examples illustrating the simulator's capabilities are given. The results show that the simulated time series and rain rate fields look realistic and that they are difficult to distinguish from real observations.
      PubDate: 2014-03-18T10:49:14.342403-05:
      DOI: 10.1002/2013WR014641
  • Real‐time global flood estimation using satellite‐based
           precipitation and a coupled land surface and routing model
    • Authors: Huan Wu; Robert F. Adler, Yudong Tian, George J. Huffman, Hongyi Li, JianJian Wang
      Pages: n/a - n/a
      Abstract: A widely used land surface model, the Variable Infiltration Capacity (VIC) model, is coupled with a newly developed hierarchical dominant river tracing‐based runoff‐routing model to form the Dominant river tracing‐Routing Integrated with VIC Environment (DRIVE) model, which serves as the new core of the real‐time Global Flood Monitoring System (GFMS). The GFMS uses real‐time satellite‐based precipitation to derive flood‐monitoring parameters for the latitude‐band 50°N‐50°S at relatively high spatial (~12km) and temporal (3‐hourly) resolution. Examples of model results for recent flood events are computed using the real‐time GFMS ( To evaluate the accuracy of the new GFMS, the DRIVE model is run retrospectively for 15 years using both research‐quality and real‐time satellite precipitation products. Evaluation results are slightly better for the research‐quality input and significantly better for longer duration events (three‐day events vs. one‐day events). Basins with fewer dams tend to provide lower false alarm ratios. For events longer than three days in areas with few dams, the probability of detection is ~0.9 and the false alarm ratio is ~0.6. In general, these statistical results are better than those of the previous system. Streamflow was evaluated at 1,121 river gauges across the quasi‐global domain. Validation using real‐time precipitation across the tropics (30ºS–30ºN) gives positive daily Nash‐Sutcliffe Coefficients for 107 out of 375 (28%) stations with a mean of 0.19 and 51% of the same gauges at monthly scale with a mean of 0.33. There were poorer results in higher latitudes, probably due to larger errors in the satellite precipitation input.
      PubDate: 2014-03-15T06:26:10.376007-05:
      DOI: 10.1002/2013WR014710
  • Effects of substrate on cracking patterns and dynamics in desiccating clay
    • Authors: Keita F. DeCarlo; Nima Shokri
      Pages: n/a - n/a
      Abstract: Desiccation cracking is ubiquitous in many materials of practical importance, such as in mud, clay soil, pavement and concrete, and understanding its dynamics and formation is essential for developing an effective means of its prevention or utilization. We report on a phenomenological investigation aimed at delineating the effect of a coarse‐textured substrate on the cracking dynamics and morphology of an overlying kaolinite clay layer. Drying experiments were carried out using a glass container mounted on a digital balance, packed with a thin layer of kaolinite clay overlying seven types of sand that differed in their particle size distributions. An automatic imaging system recorded the dynamics of cracking at the evaporating surface. Dynamics analysis suggests a decreased duration of cracking with increased substrate particle size, and substrate‐independent initial crack propagation. Analysis of the cracking morphology indicates a decreased crack density and larger crack length, and an increased crack width mean and standard deviation with increased substrate particle size. Scanning electron microscopy results, used to study the extent of cracking over various length scales, indicate that only macroscopic cracks formed on the kaolinite clay surface. Fractal and density correlation function analysis of the final crack networks indicate the dependency of the fractal dimension on the substrate particle size, and a crossover length scale ξ that separates the fractal regime from the uniform crack density regime. For length scales greater than ξ, the density correlation function asymptotically approaches the crack density at the surface of the clay.
      PubDate: 2014-03-15T06:25:37.512656-05:
      DOI: 10.1002/2013WR014466
  • Hydrologic controls on basin‐scale distribution of benthic
    • Authors: Serena Ceola; Enrico Bertuzzo, Gabriel Singer, Tom J. Battin, Alberto Montanari, Andrea Rinaldo
      Pages: n/a - n/a
      Abstract: Streamflow variability is a major determinant of basin‐scale distributions of benthic invertebrates. Here we present a novel procedure based on a probabilistic approach aiming at a spatially explicit quantitative assessment of benthic invertebrate abundance as derived from near‐bed flow variability. Although the proposed approach neglects ecological determinants other than hydraulic ones, it is nevertheless relevant in view of its implications on the predictability of basin‐scale patterns of organisms. In the present context, aquatic invertebrates are considered, given that they are widely employed as sensitive indicators of fluvial ecosystem health and human‐induced perturbations. Moving from the analytical characterization of site‐specific probability distribution functions of streamflow and bottom shear stress, we achieve a spatial extension to an entire stream network. Bottom shear stress distributions, coupled with habitat suitability curves derived from field studies, are used to produce maps of invertebrate suitability to shear stress conditions. Therefore, the proposed framework allows one to inspect the possible impacts on river ecology of human‐induced perturbations of streamflow variability. We apply this framework to an Austrian river network for which rainfall and streamflow time series, river network hydraulic properties and local information on invertebrate abundance for a limited number of sites are available. A comparison between observed species density versus modeled suitability to shear stress is also presented. Although the proposed strategy focuses on a single controlling factor and thus represents an ecological minimal model, it allows derivation of important implications for water resource management and fluvial ecosystem protection.
      PubDate: 2014-03-15T04:55:20.468143-05:
      DOI: 10.1002/2013WR015112
  • LiDAR‐derived snowpack data sets from mixed conifer forests across
           the Western United States
    • Authors: A. A. Harpold; Q. Guo, N. Molotch, P. D. Brooks, R. Bales, J. C. Fernandez‐Diaz, K. N. Musselman, T. L. Swetnam, P. Kirchner, M. W. Meadows, J. Flanagan, R. Lucas
      Pages: n/a - n/a
      Abstract: Airborne‐based Light Detection and Ranging (LiDAR) offers the potential to measure snow depth and vegetation structure at high spatial resolution over large extents and thereby increase our ability to quantify snow water resources. Here we present airborne LiDAR data products at four Critical Zone Observatories (CZO) in the Western United States: Jemez River Basin, NM, Boulder Creek Watershed, CO, Kings River Experimental Watershed, CA, and Wolverton Basin, CA. We make publicly available snow depth data products (1 m2 resolution) derived from LiDAR with an estimated accuracy of
      PubDate: 2014-03-14T17:32:26.564426-05:
      DOI: 10.1002/2013WR013935
  • Dual role of salt marsh retreat: Long‐term loss and short‐term
    • Authors: G. Mariotti; J. Carr
      Pages: n/a - n/a
      Abstract: Two major causes of salt marsh loss are vertical drowning, when sediment accumulation on the platform cannot keep vertical pace with sea level rise, and horizontal retreat, associated with wave‐induced marsh boundary erosion. Despite these processes having been extensively documented and modeled, is unclear which loss modality dominates given a set of environmental parameters. A three‐point dynamic model was developed to predict marsh loss as a function of sea level rise, allochthonous sediment supply, wind regime, tidal range, and marsh bank and mudflat erodability. Marsh horizontal and vertical evolution was found to respond in opposing ways to wave induced erosion processes. Marsh horizontal retreat was triggered by large mudflats, strong winds, high erodability of marsh bank and mudflat, whereas the opposite conditions acted to reduce the sediment supply to the marsh platform, promoting marsh loss to drowning. With low and moderate rates of sea level rise (~ 5 mm/yr), retreat was found to be a more likely marsh loss modality than drowning. However, conditions associated with marsh retreat also increase the system resilience by transferring sediment on the marsh platform and preventing drowning. Our results suggest the use of a modular strategy for short‐term marsh management: selectively protect extensive salt marsh regions by maintaining healthy vegetation on the platform, while allowing other areas to retreat, leveraging the natural resilience embedded in the lateral loss of marsh extent.
      PubDate: 2014-03-13T03:35:18.184692-05:
      DOI: 10.1002/2013WR014676
  • Role of extreme snowfall events in interannual variability of snowfall
           accumulation in the western United States
    • Authors: A. C. Lute; J. T. Abatzoglou
      Pages: n/a - n/a
      Abstract: Water resources in the western United States are contingent on interannual variations in snowpack. Interannual snowpack variability has been attributed to large‐scale climate patterns including the El Niño‐Southern Oscillation (ENSO), however the contribution of snowfall frequency and extreme snowfall events to this variability are less well quantified. Long term records from Snowpack Telemetry and Cooperative Observer Program stations in the eleven western states were used to investigate these relationships by considering the number of snowfall days and snowfall water equivalent (SFE) of extreme snowfall events. The top decile of snowfall events contributed 20‐38% of annual SFE, depending on the region. An average of 65% and 69% of the interannual variability in annual SFE was explained by snowfall days and SFE of top decile snowfall events, respectively, with extreme events being a more significant predictor at most stations. The latitudinal dipole in SFE during ENSO phases results from changes in snowfall frequency and extreme events. In the Pacific Northwest, above normal SFE during La Niña winters was a product of both larger contributions from extremes and more snowfall days, while below normal SFE during El Niño winters was primarily associated with a substantial reduction in extremes. Conversely, annual SFE during ENSO phases in the mountains of Arizona was more closely linked to fluctuations in snowfall days than extremes. Results indicate the importance of extreme snowfall events in shaping interannual variability in water resources and suggest that improved predictive ability may inform better water resource management now and in the coming decades.
      PubDate: 2014-03-13T03:22:39.085132-05:
      DOI: 10.1002/2013WR014465
  • Contribution of impervious surfaces to urban evaporation
    • Authors: P. Ramamurthy; E. Bou‐Zeid
      Pages: n/a - n/a
      Abstract: Observational data and the Princeton Urban Canopy Model, with its detailed representation of urban heterogeneity and hydrological processes, are combined to study evaporation and turbulent water vapor transport over urban areas. The analyses focus on periods before and after precipitation events, at two sites in the Northeastern United States. Our results indicate that while evaporation from concrete pavements, building rooftops and asphalt surfaces is discontinuous and intermittent, overall these surfaces accounted for nearly 18% of total latent heat fluxes (LE) during a relatively wet 10‐day period. More importantly, these evaporative fluxes have a significant impact on the urban surface energy balance, particularly during the 48 hours following a rain event when impervious evaporation is the highest. Thus, their accurate representation in urban models is critical. Impervious evaporation after rainfall is also shown to correlate the sources of heat and water at the earth surface, resulting in a conditional scalar transport similarity over urban terrain following rain events.
      PubDate: 2014-03-13T03:22:30.03935-05:0
      DOI: 10.1002/2013WR013909
  • Assessing the impact of model spin‐up on surface
    • Authors: Hoori Ajami; Mathew F. McCabe, Jason P. Evans, Simon Stisen
      Pages: n/a - n/a
      Abstract: Integrated land surface‐groundwater models are valuable tools in simulating the terrestrial hydrologic cycle as a continuous system and exploring the extent of land surface–subsurface interactions from catchment to regional scales. However, the fidelity of model simulations is impacted not only by the vegetation and subsurface parameterizations, but also by the antecedent condition of model state variables, such as the initial soil moisture, depth to groundwater and ground temperature. In land surface modeling, a given model is often run repeatedly over a single year of forcing data until it reaches an equilibrium state: the point at which there is minimal artificial drift in the model state or prognostic variables (most often the soil moisture). For more complex coupled and integrated systems, where there is an increased computational cost of simulation and the number of variables sensitive to initialization is greater than in traditional uncoupled land surface modeling schemes, the challenge is to minimize the impact of initialization while using the smallest spin‐up time possible. In this study, multi‐criteria analysis was performed to assess the spin‐up behavior of the ParFlow.CLM integrated groundwater‐surface water‐land surface model over a 208 km2 sub‐catchment of the Ringkobing Fjord catchment in Denmark. Various measures of spin‐up performance were computed for model state variables such as the soil moisture and groundwater storage, as well as for diagnostic variables such as the latent and sensible heat fluxes. The impacts of initial conditions on surface water–groundwater interactions were then explored. Our analysis illustrates that the determination of an equilibrium state depends strongly on the variable and performance measure used. Choosing an improper initialization of the model can generate simulations that lead to a misinterpretation of land surface‐subsurface feedback processes and result in large biases in simulated discharge. Estimated spin‐up time from a series of spin‐up functions revealed that 20 (or 21) years of simulation were sufficient for the catchment to equilibrate according to at least one criterion at the 0.1% (0.01%) threshold level. Amongst a range of convergence metrics examined, percentage changes in monthly values of groundwater and unsaturated zone storages produced a slow system convergence to equilibrium, whereas criteria based on ground temperature allowed a more rapid spin‐up. Slow convergence of unsaturated and saturated zone storages is a result of the dynamic adjustment of the water table in response to a physically arbitrary or inconsistent initialization of a spatially uniform water table. Achieving equilibrium in subsurface storage ensured equilibrium across a spectrum of other variables, hence providing a good measure of system‐wide equilibrium. Overall, results highlight the importance of correctly identifying the key variable affecting model equilibrium and also the need to use a multi‐criteria approach to achieve a rapid and stable model spin‐up.
      PubDate: 2014-03-12T07:30:46.378609-05:
      DOI: 10.1002/2013WR014258
  • Multiple hydrological attractors under stochastic daily forcing: 2. Can
           multiple attractors emerge?
    • Authors: T. J. Peterson; A. W. Western, R. M. Argent
      Pages: n/a - n/a
      Abstract: The companion paper showed that multiple steady state groundwater levels can exist within a hill‐slope Boussinesq‐vegetation model under daily stochastic forcing. Using a numerical limit‐cycle continuation algorithm, the steady states (henceforth attractors) and the threshold between them (henceforth repellor) were quantified at a range of saturated lateral conductivity values, ksmax⁡. This paper investigates if stochastic daily forcing can switch the catchment between both of the attractors. That is, an attractor may exist under average forcing conditions but can stochastic forcing switch the catchment into and out of each of the attractor basins?; i.e. making the attractor emerge. This was undertaken using the model of the companion paper and by completing daily time‐integration simulations at six values of the saturated lateral hydraulic conductivity, ksmax⁡; three having two attractors and three having only a deep water table attractor. By graphically analyzing the simulations, and comparing against simulations from a model modified to have only one attractor, multiple attractors were found to emerge under stochastic daily forcing. However, the emergence of attractors was significantly more subtle and complex than that suggested by the companion paper. That is, an attractor may exist but never emerge; both attractors may exist and both may emerge but identifying the switching between attractors was often ambiguous; and only one attractor may exist and but a second temporary attractor may exist and emerge during periods of high precipitation. This subtle and complex emergence of attractors was explained using continuation analysis of the climate forcing rate, and not a model parameter such as ksmax⁡. It showed that the temporary attractor existed over a large range of ksmax⁡ values and this suggests that more catchments may have multiple attractors than suggested by the companion paper. By combining this continuation analysis with the time‐integration simulations, hydrological signatures indicative of a switch of multiple attractors were proposed. These signatures may provide a means for identifying actual catchments that have switched between multiple attractors.
      PubDate: 2014-03-10T12:49:17.753868-05:
      DOI: 10.1002/2012WR013004
  • Multiple hydrological attractors under stochastic daily forcing: 1. Can
           multiple attractors exist?
    • Authors: T. J. Peterson; A. W. Western
      Pages: n/a - n/a
      Abstract: Including positive feedbacks in hydrological models has recently been shown to result in complex behavior with multiple steady states. When a large disturbance, say a major drought, is simulated within such models the hydrology changes. Once the disturbance ends the hydrology does not return to that prior to the disturbance, but rather, persists within an alternate state. These multiple steady states (henceforth attractors) exist for a single model parameterization and cause the system to have a finite resilience to such transient disturbances. A limitation of past hydrological resilience studies is that multiple attractors have been identified using mean annual or mean monthly forcing. Considering that most hydrological fluxes are subject to significant forcing stochasticity and do not operate at such large time scales, it remains an open question whether multiple hydrological attractors can exist when a catchment is subject to stochastic daily forcing. This question is the focus of this paper and it needs to be addressed prior to searching for multiple hydrological attractors in the field. To investigate this, a previously developed semi‐distributed hill‐slope ecohydrological model was adopted which exhibited multiple steady states under average monthly climate forcing. In this paper, the ecohydrological model was used to explore if feedbacks between the vegetation and a saline water table result in two attractors existing under daily stochastic forcing. The attractors and the threshold between them (henceforth repellor) were quantified using a new limit cycle continuation technique that up‐scaled climate forcing from daily to monthly (model and limit cycle code is freely available). The method was used to determine the values of saturated lateral hydraulic conductivity at which multiple attractors exist. These estimates were then assessed against time‐integration estimates, which they agreed with. Overall, multiple attractors where found to exist under stochastic daily forcing. However, changing the climate forcing from monthly to daily did significantly reduce the parameter range over which two attractors existed. This suggests fewer catchments may have multiple attractors than previously considered.
      PubDate: 2014-03-10T12:29:50.626255-05:
      DOI: 10.1002/2012WR013003
  • Three‐dimensional imaging of subsurface structural patterns using
           quantitative large‐scale multiconfiguration electromagnetic
           induction data
    • Authors: Christian Hebel; Sebastian Rudolph, Achim Mester, Johan A. Huisman, Pramod Kumbhar, Harry Vereecken, Jan Kruk
      Pages: n/a - n/a
      Abstract: Electromagnetic induction (EMI) systems measure the soil apparent electrical conductivity (ECa), which is related to the soil water content, texture and salinity changes. Large‐scale EMI measurements often show relevant areal ECa patterns, but only few researchers have attempted to resolve vertical changes in electrical conductivity that in principle can be obtained using multi‐configuration EMI devices. In this work, we show that EMI measurements can be used to determine the lateral and vertical distribution of the electrical conductivity at the field scale and beyond. Processed ECa data for six coil configurations measured at the Selhausen (Germany) test site were calibrated using inverted electrical resistivity tomography (ERT) data from a short transect with a high ECa range, and re‐gridded using a nearest neighbor interpolation. The quantitative ECa data at each grid node were inverted using a novel three‐layer inversion that uses the shuffled complex evolution (SCE) optimization and a Maxwell‐based electromagnetic forward model. The obtained 1D‐results were stitched together to form a quasi‐3D subsurface electrical conductivity model that showed smoothly varying electrical conductivities and layer thicknesses, indicating the stability of the inversion. The obtained electrical conductivity distributions were validated with low resolution grain size distribution maps and two 120 m long ERT transects that confirmed the obtained lateral and vertical large‐scale electrical conductivity patterns. Observed differences in the EMI and ERT inversion results were attributed to differences in soil water content between acquisition days. These findings indicate that EMI‐inversions can be used to infer hydrologically active layers.
      PubDate: 2014-03-06T05:08:51.17506-05:0
      DOI: 10.1002/2013WR014864
  • A simple approach to the evaluation of the actual water renewal time of
           natural stratified lakes
    • Authors: Marco Pilotti; Stefano Simoncelli, Giulia Valerio
      Pages: n/a - n/a
      Abstract: In natural lakes where thermal stratification hinders complete mixing, the theoretical value T0 of the water renewal time provides a low order approximation to the time T37 when 37% of the original water is still present within the lake; this time could be operatively regarded as the actual value of the water renewal time. In this paper we present a simple non parametric model to estimate the age distribution of water within stratified natural lakes, taking into account fundamental aspects of its mass exchange and thermal evolution. This distribution provides a straightforward way to compute T37. The model is presented as a system of ordinary differential equations along with a MATLAB script for its numerical solution, so that it can be easily applied to lakes where a minimum of limnological data are available, without the need of extensive meteorological data set and modelling expertise that an hydrodynamic model would require to the same purpose. The case of a deep oligomictic Italian prealpine lake (Lake Iseo) is considered: after a positive comparison with the results obtained using a 1‐D lake hydrodynamic model, the reiterated application to the available time series allows to approximate the water age probability distribution. This distribution is used to compute the actual value of the water renewal time, that resulted T37=1.6T0.
      PubDate: 2014-03-05T22:37:29.934174-05:
      DOI: 10.1002/2013WR014471
  • Issue Information
    • Pages: i - vi
      PubDate: 2014-02-25T11:22:01.89423-05:0
      DOI: 10.1002/wrcr.20472
  • Analytical basis for determining slope lines in grid digital elevation
    • Authors: Stefano Orlandini; Giovanni Moretti, Andrea Gavioli
      Pages: n/a - n/a
      Abstract: An analytical basis for the determination of slope lines in grid digital elevation models is provided by using the D8‐LTD method (eight slope directions, least transverse deviation). The D8‐LTD method's capability to predict consistently exact slope lines as the grid cell size goes to zero is shown analytically by applying mathematical analysis methods. The use of cumulative, least transverse deviations is found to be the key factor allowing for globally unbiased approximations of slope lines. The D8‐LTD method's properties are also demonstrated numerically by using digital elevation models of a synthetic sloping surface obtained from the Himmelblau function. It is shown that slope lines obtained from the D8‐LTD method can approximate the exact slope lines as close as desired by selecting a grid cell size that is small enough. In contrast, the standard D8 method is found to produce significantly biased results even when small grid cells are used. The D8‐LTD method outperforms the D8 method over a wide range of grid cell sizes (up to 20 m in this application), beyond which grid cell size becomes too large to validly represent the underlying sloping surface. It is therefore concluded that the D8‐LTD method should be used in preference to the standard D8 method in order to obtain slope lines that are only limited in reliability by the detail of topographic data, and not by the accuracy of the slope direction method applied.
      PubDate: 2014-01-22T12:00:45.620974-05:
      DOI: 10.1002/2013WR014606
  • Quantification of surface energy fluxes from a small water body using
           scintillometry and eddy covariance
    • Authors: Ryan McGloin; Hamish McGowan, David McJannet, Freeman Cook, Andrey Sogachev, Stewart Burn
      Pages: n/a - n/a
      Abstract: Accurate quantification of evaporation from small water storages is essential for water management and planning, particularly in water‐scarce regions. In order to ascertain suitable methods for direct measurement of evaporation from small water bodies, this study presents a comparison of eddy covariance and scintillometry measurements from a reservoir in southeast Queensland, Australia. The work presented expands on a short study presented by McJannet et al. (2011) to include comparisons of eddy covariance measurements and scintillometer‐derived predictions of surface energy fluxes under a wide range of seasonal weather conditions. In this study, analysis was undertaken to ascertain whether important theoretical assumptions required for both techniques are valid in the complex environment of a small reservoir. Statistical comparison, energy balance closure, and the relationship between evaporation measurements and key environmental controls were used to compare the results of the two techniques. Reasonable agreement was shown between the sensible heat flux measurements from eddy covariance and scintillometry, while scintillometer‐derived estimates of latent heat flux were approximately 21% greater than eddy covariance measurements. We suggest possible reasons for this difference and provide recommendations for further research for improving measurements of surface energy fluxes over small water bodies using eddy covariance and scintillometry.
      PubDate: 2014-01-21T17:46:57.993581-05:
      DOI: 10.1002/2013WR013899
  • Assessing invertebrate assemblages in the subsurface zone of stream
           sediments (0–15 cm deep) using a hyporheic sampler
    • Authors: Marie‐José Dole‐Olivier; Chafik Maazouzi, Bernard Cellot, Frank Fiers, Diana M. P. Galassi, Cécile Claret, Dominique Martin, Sylvie Mérigoux, Pierre Marmonier
      Pages: n/a - n/a
      Abstract: Quantitative comparisons between benthic and hyporheic invertebrate communities are crucial for understanding the biological functions of the hyporheic zone, such as storage, migrations, and exchanges of invertebrates with the surface stream. Such comparisons are still hampered by the use of different techniques adapted to each habitat (benthic versus hyporheic). This work combines two different techniques for sampling the upper layers of bed sediments (0–15 cm): the semiquantitative “Bou‐Rouch” pump classically used to sample the hyporheic zone (>15 cm), and the quantitative Hess sampler commonly used to sample the benthic zone (≤15 cm), in order to evaluate the quantitative efficiency of the pump in this 0–15 cm zone. First, a Bou‐Rouch sample (BR) was taken within the cylinder of a Hess inserted within the streambed, then a second sample (benthic complement, BC) was collected within the Hess after removing the pump, in order to catch all invertebrates not extracted with the pump. The BR samples collected on average 14.5% of the total abundance and about 50% of the actual richness. The large range of variation indicates that the combination of the two techniques is not valid for a quantitative evaluation of benthic communities. Contrary to expectations, the pump did not collect more interstitial and groundwater invertebrates and no differences in faunal composition between upstream and downstream riffle positions were observed. Our results do not question the use of the BR technique under standard conditions i.e., when sampling the hyporheic zone, but underline how it is crucial to know its quantitative limits.
      PubDate: 2014-01-21T17:19:09.646864-05:
      DOI: 10.1002/2012WR013207
  • Lithologic influences on groundwater recharge through incised glacial till
    • Authors: John B. Gates; Gregory V. Steele, Paolo Nasta, Jozsef Szilagyi
      Pages: n/a - n/a
      Abstract: Variability in sediment hydraulic properties associated with landscape depositional and erosional features can influence groundwater recharge processes by affecting soil‐water storage and transmission. This study considers recharge to aquifers underlying river‐incised glaciated terrain where the distribution of clay‐rich till is largely intact in upland locations but has been removed by alluvial erosion in stream valleys. In a stream‐dissected glacial region in eastern Nebraska (Great Plains region of the United States), recharge estimates were developed for nested profile, aquifer, and regional scales using unsaturated zone profile measurements (matric potentials, Cl− and 3H), groundwater tracers (CFC‐12 and SF6), and a remote sensing‐assisted water balance model. Results show a consistent influence of till lithology on recharge rates across nested spatial scales despite substantial uncertainty in all recharge estimation methods, suggesting that minimal diffuse recharge occurs through upland glacial till lithology whereas diffuse recharge occurs in river valleys where till is locally absent. Diffuse recharge is estimated to account for a maximum of 61% of total recharge based on comparison of diffuse recharge estimated from the unsaturated zone (0–43 mm yr−1) and total recharge estimated from groundwater tracers (median 58 mm yr−1) and water balance modeling (median 56 mm yr−1). The results underscore the importance of lithologic controls on the distributions of both recharge rates and mechanisms.
      PubDate: 2014-01-21T17:02:34.591292-05:
      DOI: 10.1002/2013WR014073
  • Downstream changes in DOC: Inferring contributions in the face of model
    • Authors: Tejshree Tiwari; Hjalmar Laudon, Keith Beven, Anneli M. Ågren
      Pages: n/a - n/a
      Abstract: Dissolved organic carbon (DOC) is a central constituent of surface waters which control its characteristic color and chemistry. While the sources and controls of headwater stream DOC can be mechanistically linked to the dominant landscape types being drained, much remains unknown about the downstream controls at larger spatial scales. As DOC is transported from the headwaters to catchment outlets, the fate of stream DOC is largely dependent on the interaction of varying catchment processes. In this study, we investigated the main mechanisms regulating stream DOC in a mesoscale catchment. A landscape‐mixing model was used to test the role of landscapes in determining stream concentrations. The quantity of DOC lost to in‐stream processes was calculated using bacterial respiration and photooxidation rates. We investigated whether there was a change in water pathways using a mass balance model and comparison of hydrology between a headwater catchment and the entire catchment. A Monte Carlo approach was used to test robustness of the model assumptions and results to uncertainty in the process parameterizations. The results indicated that during high‐ and intermediate‐flow conditions, DOC concentrations were regulated by the contributing upstream landscape types. During base flow, the connectivity between the mesoscale river and the upstream landscape reduced resulting in large residuals in the landscape model which could not be explained by the in‐stream processes. Both the mass balance model and a specific runoff comparison between upstream/downstream sites independently indicated large input of deep groundwater during base flow. Deep groundwater was important for diluting stream DOC concentrations during base flow.
      PubDate: 2014-01-21T14:39:09.083424-05:
      DOI: 10.1002/2013WR014275
  • Transverse spatiotemporal variability of lowland river properties and
           effects on metabolic rate estimates
    • Authors: Sandra R. Villamizar; Henry Pai, Christopher A. Butler, Thomas C. Harmon
      Pages: n/a - n/a
      Abstract: Variability of river properties such as temperature, velocity, dissolved oxygen (DO), and light at small scales (centimeters to meters) can play an important role in the local exchanges of energy and mass. We hypothesize that significant transverse cross‐sectional DO variation is observable within a river. Such variation may influence conventional single‐station metabolic rate (primary production and respiration) estimates with respect to DO probe location, and reveal important connections between physical and biogeochemical processes and their drivers in rivers. Using a mobile sensor system, we measured river properties across a bend in the lower Merced River in Central California under stationary flow conditions in April and September. Cross‐sectional temperature, DO, and chlorophyll‐a concentrations exhibited modest but significant gradients, which varied in magnitude and direction on a diel basis. The spatiotemporal variation was consistent with reach geomorphology and incident light patterns. Gross primary production (GPP), community respiration (CR24), and net ecosystem production (NEP) rates estimates derived from local DO and temperature time series varied by 3–10% over the river cross section, with greater variation in late summer. The presence of transverse metabolic rate gradients in this relatively simple reach implies the existence of substantial gradients in more complex river regimes, such as those spanning distinctively different microhabitats, transient storage zones, and related distributed biogeochemical zones.
      PubDate: 2014-01-21T12:26:08.699661-05:
      DOI: 10.1002/2013WR014245
  • Comparison of prognostic and diagnostic surface flux modeling approaches
           over the Nile River basin
    • Authors: M. Tugrul Yilmaz; Martha C. Anderson, Ben Zaitchik, Chris R. Hain, Wade T. Crow, Mutlu Ozdogan, Jong Ahn Chun, Jason Evans
      Pages: n/a - n/a
      Abstract: Regional evapotranspiration (ET) can be estimated using diagnostic remote sensing models, generally based on principles of energy balance closure, or with spatially distributed prognostic models that simultaneously balance both energy and water budgets over landscapes using predictive equations for land surface temperature and moisture states. Each modeling approach has complementary advantages and disadvantages, and in combination they can be used to obtain more accurate ET estimates over a variety of land and climate conditions, particularly for areas with limited ground truth data. In this study, energy and water flux estimates from diagnostic Atmosphere‐Land Exchange (ALEXI) and prognostic Noah land surface models are compared over the Nile River basin between 2007 and 2011. A second remote sensing data set, generated with Penman‐Monteith approach as implemented in the Moderate Resolution Imaging Spectroradiometer (MODIS) MOD16 ET product, is also included as a comparative technique. In general, spatial and temporal distributions of flux estimates from ALEXI and Noah are similar in regions where the climate is temperate and local rainfall is the primary source of water available for ET. However, the diagnostic ALEXI model is better able to retrieve ET signals not directly coupled with the local precipitation rates, for example, over irrigated agricultural areas or regions influenced by shallow water tables. These hydrologic features are not well represented by either Noah or MOD16. Evaluation of consistency between diagnostic and prognostic model estimates can provide useful information about relative product skill, particularly over regions where ground data are limited or nonexistent as in the Nile basin.
      PubDate: 2014-01-17T16:34:51.683029-05:
      DOI: 10.1002/2013WR014194
  • Sensitivity analysis of SCHADEX extreme flood estimations to observed
           hydrometeorological variability
    • Authors: Pierre Brigode; Pietro Bernardara, Emmanuel Paquet, Joël Gailhard, Federico Garavaglia, Ralf Merz, Zoran Mićović, Deborah Lawrence, Pierre Ribstein
      Pages: n/a - n/a
      Abstract: Stochastic flood simulation methods are typically based on a rainfall probabilistic model (used for simulating continuous rainfall series or for estimating probabilities of random rainfall events) and on a rainfall‐runoff model. Usually, both of these models are calibrated over observed hydrometeorological series, which may be subject to significant variability and/or nonstationarity over time. The general aim of this study is thus to propose and test a methodology for performing a sensitivity analysis of extreme flood estimations to observed hydrometeorological variability. The methodology consists of performing a set of block‐bootstrap experiments: for each experiment, the data used for calibration of a particular model (e.g., the rainfall probabilistic model) is bootstrapped while the model structure and the calibration process are held constant. The SCHADEX extreme flood estimation method has been applied over six catchments located in different regions of the world. The results show first that the variability of observed rainfall hazard has the most significant impact on the extreme flood estimates. Then, consideration of different rainfall‐runoff calibration periods generates a significant spread of extreme flood estimated values. Finally, the variability of the catchment saturation hazard has a nonsignificant impact on the extreme flood estimates. An important point raised by this study is the dominating role played by outliers within the observed records for extreme flood estimation.
      PubDate: 2014-01-17T16:34:30.786512-05:
      DOI: 10.1002/2013WR013687
  • The Auto‐Tuned Land Data Assimilation System (ATLAS)
    • Authors: W. T. Crow; M. Tugrul Yilmaz
      Pages: n/a - n/a
      Abstract: Land data assimilation systems are commonly tasked with merging remotely sensed surface soil moisture retrievals with information derived from a soil water balance model driven by observed rainfall. The performance of such systems can be degraded by the incorrect specification of parameters describing modeling and observation errors. Here the Auto‐Tuned Land Data Assimilation System (ATLAS) is introduced to simultaneously solve for all parameters required for the application of a simple land data assimilation system to integrate satellite‐based rainfall and soil moisture retrievals for drought monitoring applications. The approach is based on combining a triple collocation (TC) strategy with the statistical analysis of filtering innovations and designed to leverage the simultaneous availability of satellite‐based soil moisture products acquired from both active and passive microwave remote sensing. A number of variants of the ATLAS approach—each based on a different strategy for leveraging TC and innovation analysis within an adaptive filtering framework—are derived and evaluated through a synthetic twin experiment. In addition, a preliminary real data analysis is conducted using actual satellite‐based products and evaluated against independent ground‐based observations. Results illustrate the potential of ATLAS to improve the analysis of soil moisture anomalies using data products derived from the Global Precipitation Measurement (GPM) and the NASA Soil Moisture Active/Passive missions.
      PubDate: 2014-01-17T16:30:55.125817-05:
      DOI: 10.1002/2013WR014550
  • Pore‐space alteration induced by brine acidification in subsurface
           geologic formations
    • Authors: Saeed Ovaysi; Mohammad Piri
      Pages: n/a - n/a
      Abstract: A new Lagrangian particle‐based method is presented to simulate reactive transport in natural porous media. This technique is based on Modified Moving Particle Semi‐implicit (MMPS) and takes as input high‐resolution voxel images of natural porous media. The flow field in the medium is computed by solving the incompressible Navier‐Stokes equations. Moreover, a multicomponent ion transport model is coupled with a homogeneous and heterogeneous reactions module to handle pore‐space alteration (i.e., pore‐wall dissolution). The model is first successfully validated against the experimental data available in the literature. Subsequently, X‐ray microtomographic images of two naturally occurring porous media are used to investigate the impact of reaction kinetics and pore‐space topology on pore‐space alteration induced by brine acidification in subsurface conditions. We observed that at the normal rates of reactions no significant change in porosity and permeability takes place in the short term. Whereas, higher reaction rates caused major changes in the macroscopic properties (e.g., porosity and permeability) of the rocks. We also show that these changes are strongly affected by the rocks' pore‐scale topologies.
      PubDate: 2014-01-17T16:30:33.476779-05:
      DOI: 10.1002/2013WR014289
  • Modeling point velocity and depth statistical distributions in steep
           tropical and alpine stream reaches
    • Authors: V. Girard; N. Lamouroux, R. Mons
      Pages: n/a - n/a
      Abstract: Statistical hydraulic models predict the frequency distributions of point hydraulic variables, relative to their reach‐averaged values, in a stream reach based on its average characteristics (e.g., discharge, depth, width, average particle size). The models initially developed in Europe have not been tested for steeper streams (>4%) with coarse grain size. We recorded water velocities and depths in 44 reaches of steep streams in tropical islands and the Alps during 69 surveys. We fitted the observed distributions of velocities and depths using a mixture of two distributions, one with low variance and the other with a high variance. Then, we predicted the mixing parameter on the basis of the reach‐averaged characteristics. We compared the observed and predicted frequencies for five classes of velocities, including a class of negative velocities, and four classes of water depths. The predictions of class frequencies have a bias of ≤5%. Our statistical model of velocity distribution predicts the frequencies of velocity classes with an explained variance between 33 and 72% for four classes of velocity and null for a class of intermediate velocity. The statistical model of depth distributions was less efficient with an explained variance between 25 and 38% for three classes of depth and null for large depths. The average Froude number, the total height of large drops relative to the reach length and the average slope are the main explanatory variables of velocity and depth distributions.
      PubDate: 2014-01-17T15:04:05.864828-05:
      DOI: 10.1002/2013WR013894
  • Distributed evaluation of local sensitivity analysis (DELSA), with
           application to hydrologic models
    • Authors: O. Rakovec; M. C. Hill, M. P. Clark, A. H. Weerts, A. J. Teuling, R. Uijlenhoet
      Pages: n/a - n/a
      Abstract: This paper presents a hybrid local‐global sensitivity analysis method termed the Distributed Evaluation of Local Sensitivity Analysis (DELSA), which is used here to identify important and unimportant parameters and evaluate how model parameter importance changes as parameter values change. DELSA uses derivative‐based “local” methods to obtain the distribution of parameter sensitivity across the parameter space, which promotes consideration of sensitivity analysis results in the context of simulated dynamics. This work presents DELSA, discusses how it relates to existing methods, and uses two hydrologic test cases to compare its performance with the popular global, variance‐based Sobol' method. The first test case is a simple nonlinear reservoir model with two parameters. The second test case involves five alternative “bucket‐style” hydrologic models with up to 14 parameters applied to a medium‐sized catchment (200 km2) in the Belgian Ardennes. Results show that in both examples, Sobol' and DELSA identify similar important and unimportant parameters, with DELSA enabling more detailed insight at much lower computational cost. For example, in the real‐world problem the time delay in runoff is the most important parameter in all models, but DELSA shows that for about 20% of parameter sets it is not important at all and alternative mechanisms and parameters dominate. Moreover, the time delay was identified as important in regions producing poor model fits, whereas other parameters were identified as more important in regions of the parameter space producing better model fits. The ability to understand how parameter importance varies through parameter space is critical to inform decisions about, for example, additional data collection and model development. The ability to perform such analyses with modest computational requirements provides exciting opportunities to evaluate complicated models as well as many alternative models.
      PubDate: 2014-01-17T15:00:34.103415-05:
      DOI: 10.1002/2013WR014063
  • Finite volume‐integrated surface‐subsurface flow modeling on
           nonorthogonal grids
    • Authors: Hyunuk An; Soonyoung Yu
      Pages: n/a - n/a
      Abstract: In this paper, we present an innovative finite volume surface‐subsurface integrated flow model on non‐orthogonal grids. The shallow water equation with diffusion wave approximation is used to formulate the surface flow system, while the Richards' equation is used to formulate the saturated‐unsaturated subsurface flow system. These two flow systems are discretized using a finite volume method, and are then coupled by enforcing the continuity of pressure and flux at the surface‐subsurface interface, which does not require unphysical parameters such as the interface permeability and thickness. The numerical instability caused by enforcing the continuity of pressure and flux at the interface is resolved using a cell‐centered finite volume discretization. The coupled systems are solved simultaneously by the Newton iterative method. A battery of benchmark analyses and laboratory experiments verify the proposed model's superior performance relative to existing models. Two numerical experiments over irregular terrain show that the non‐orthogonal grids and diffusive wave approximation used in the proposed model accurately represent the interaction between surface and subsurface flows for irregular topographies. In particular, they capture the significant topographical effects on runoff discharges, especially where gentle slopes are involved.
      PubDate: 2014-01-15T15:11:49.720052-05:
      DOI: 10.1002/2013WR013828
  • Long‐term snow distribution observations in a mountain catchment:
           Assessing variability, time stability, and the representativeness of an
           index site
    • Authors: Adam Winstral; Danny Marks
      Pages: n/a - n/a
      Abstract: This study presents an analysis of snow distribution heterogeneity and the factors affecting this variability. The analysis focuses on manually sampled data from 21 snow surveys covering 11 years at the drift‐dominated Reynolds Mountain East catchment (0.36 km2) in southwestern Idaho, USA. Surveys were conducted midwinter and in early spring. Interseason and intraseason trends were examined along with the time stability of distributions, goodness‐of‐fit to theoretical distributions, and the representativeness of an index site as a measure of basin‐wide snow water equivalent. The average snow depth coefficient of variation (CV) over the entire time period was 0.71, which is in accordance with broad regional assessments. Higher wind speeds during snow events and increased melt led to increased heterogeneity and higher CVs. Forested sites produced lower CVs presumably due to moderated winds at these sites. Consistent wind directions produced accumulation patterns that were very stable from year‐to‐year. Many previous studies have suggested that vital subgrid snow heterogeneity in large‐scale models can be approximated with parametric distributions. Gamma distributions were preferred over lognormal distributions in describing the overall distribution while in tree‐covered regions with less variability there was little difference between the two. It was also found that an index site, akin to the majority of North American mountain weather observation stations, provided a reasonable approximation of catchment‐averaged SWE in most years. However, the reliability of this measure decreased in years that deviated from normal patterns.
      PubDate: 2014-01-15T13:48:50.266614-05:
      DOI: 10.1002/2012WR013038
  • Calibrating hydrologic models in flow‐corrected time
    • Authors: Tyler Smith; Lucy Marshall, Brian McGlynn
      Pages: n/a - n/a
      Abstract: Modeling streamflow hydrographs can be a highly complex problem, particularly due to difficulties caused by multiple dominant streamflow states, switching of dominant streamflow generation mechanisms temporally, and dynamic catchment responses to precipitation inputs based on antecedent conditions. Because of these complexities and the extreme heterogeneity that can exist within a single catchment, model calibration techniques are generally required to obtain reasonable estimates of the model parameters. Models are typically calibrated such that a best fit is determined over the entire period of simulation. In this way, each time step explicitly carries equal weight during the calibration process. Data transformations (e.g., logarithmic or square root) are a common way of modifying the calibration process by scaling the magnitude of the observations. Here we consider a data transformation that is focused on the time domain rather than the data domain. This approach, previously employed in transit time modeling literature, conceptually stretches time during high streamflows and compresses it during low streamflow periods, dynamically weighting streamflows in the time domain. The transformation, known as flow‐corrected time, is designed to provide greater weight to time periods with larger hydrologic flux. Here the flow‐corrected time transformation is compared to a baseline untransformed case and the commonly employed logarithmic transformation. Considering both visual and numerical (Nash‐Sutcliffe efficiency) assessments, we demonstrate that over the time periods that dominate hydrologic flux the flow‐corrected time transformation resulted in improved fits to the observed hydrograph.
      PubDate: 2014-01-15T13:47:52.563389-05:
      DOI: 10.1002/2013WR014635
  • Rainfall extremes: Toward reconciliation after the battle of distributions
    • Authors: Francesco Serinaldi; Chris G. Kilsby
      Pages: n/a - n/a
      Abstract: This study attempts to reconcile the conflicting results reported in the literature concerning the behavior of peak‐over‐threshold (POT) daily rainfall extremes and their distribution. By using two worldwide data sets, the impact of threshold selection and record length on the upper tail behavior of POT observations is investigated. The rainfall process is studied within the framework of generalized Pareto (GP) exceedances according to the classical extreme value theory (EVT), with particular attention paid to the study of the GP shape parameter, which controls the heaviness of the upper tail of the GP distribution. A twofold effect is recognized. First, as the threshold decreases, and nonextreme values are progressively incorporated in the POT samples, the variance of the GP shape parameter reduces and the mean converges to positive values denoting a tendency to heavy tail behavior. Simultaneously, the EVT asymptotic hypotheses are less and less realistic, and the GP asymptote tends to be replaced by the Weibull penultimate asymptote whose upper tail is exponential but apparently heavy. Second, for a fixed high threshold, the variance of the GP shape parameter reduces as the record length (number of years) increases, and the mean values tend to be positive, thus denoting again the prevalence of heavy tail behavior. In both cases, i.e., threshold selection and record length effect, the heaviness of the tail may be ascribed to mechanisms such as the blend of extreme and nonextreme values, and fluctuations of the parent distributions. It is shown how these results provide a link between previous studies and pave the way for more comprehensive analyses which merge empirical, theoretical, and operational points of view. This study also provides several ancillary results, such as a set of formulae to correct the bias of the GP shape parameter estimates due to short record lengths accounting for uncertainty, thus avoiding systematic underestimation of extremes which results from the analysis of short time series.
      PubDate: 2014-01-15T13:47:21.683932-05:
      DOI: 10.1002/2013WR014211
  • Observations of a two‐layer soil moisture influence on surface
           energy dynamics and planetary boundary layer characteristics in a semiarid
    • Authors: Zulia Mayari Sanchez‐Mejia; Shirley A. Papuga
      Pages: n/a - n/a
      Abstract: We present an observational analysis examining soil moisture control on surface energy dynamics and planetary boundary layer characteristics. Understanding soil moisture control on land‐atmosphere interactions will become increasingly important as climate change continues to alter water availability. In this study, we analyzed 4 years of data from the Santa Rita Creosote Ameriflux site. We categorized our data independently in two ways: (1) wet or dry seasons and (2) one of the four cases within a two‐layer soil moisture framework for the root zone based on the presence or absence of moisture in shallow (0–20 cm) and deep (20–60 cm) soil layers. Using these categorizations, we quantified the soil moisture control on surface energy dynamics and planetary boundary layer characteristics using both average responses and linear regression. Our results highlight the importance of deep soil moisture in land‐atmosphere interactions. The presence of deep soil moisture decreased albedo by about 10%, and significant differences were observed in evaporative fraction even in the absence of shallow moisture. The planetary boundary layer height (PBLh) was largest when the whole soil profile was dry, decreasing by about 1 km when the whole profile was wet. Even when shallow moisture was absent but deep moisture was present the PBLh was significantly lower than when the entire profile was dry. The importance of deep moisture is likely site‐specific and modulated through vegetation. Therefore, understanding these relationships also provides important insights into feedbacks between vegetation and the hydrologic cycle and their consequent influence on the climate system.
      PubDate: 2014-01-15T12:15:43.487846-05:
      DOI: 10.1002/2013WR014135
  • Dynamic hyporheic exchange at intermediate timescales: Testing the
           relative importance of evapotranspiration and flood pulses
    • Authors: Laurel G. Larsen; Judson W. Harvey, Morgan M. Maglio
      Pages: n/a - n/a
      Abstract: Hyporheic fluxes influence ecological processes across a continuum of timescales. However, few studies have been able to characterize hyporheic fluxes and residence time distributions (RTDs) over timescales of days to years, during which evapotranspiration (ET) and seasonal flood pulses create unsteady forcing. Here we present a data‐driven, particle‐tracking piston model that characterizes hyporheic fluxes and RTDs based on measured vertical head differences. We used the model to test the relative influence of ET and seasonal flood pulses in the Everglades (FL, USA), in a manner applicable to other low‐energy floodplains or broad, shallow streams. We found that over the multiyear timescale, flood pulses that drive relatively deep (∼1 m) flow paths had the dominant influence on hyporheic fluxes and residence times but that ET effects were discernible at shorter timescales (weeks to months) as a break in RTDs. Cumulative RTDs on either side of the break were generally well represented by lognormal functions, except for when ET was strong and none of the standard distributions applied to the shorter timescale. At the monthly timescale, ET increased hyporheic fluxes by 1–2 orders of magnitude; it also decreased 6 year mean residence times by 53–87%. Long, slow flow paths driven by flood pulses increased 6 year hyporheic fluxes by another 1–2 orders of magnitude, to a level comparable to that induced over the short term by shear flow in streams. Results suggest that models of intermediate‐timescale processes should include at least two‐storage zones with different RTDs, and that supporting field data collection occur over 3–4 years.
      PubDate: 2014-01-15T10:52:58.04647-05:0
      DOI: 10.1002/2013WR014195
  • A hidden seasonal switching model for multisite daily rainfall
    • Authors: Trevor Carey‐Smith; John Sansom, Peter Thomson
      Pages: n/a - n/a
      Abstract: A hidden seasonal switching model for daily rainfall over a region is proposed where season onset times are stochastic and can vary from year to year. The model allows seasons to occur earlier or later than expected and have varying lengths. This stochastic seasonal variation accommodates considerably more of the observed intraannual rainfall variability than can be represented using seasonal models with standard fixed seasons. In essence, the model dynamically classifies daily rainfall time series into seasons whose onsets vary from year to year and within which the model parameters are assumed to be time homogeneous. A variety of nonseasonal models could have been used to describe daily rainfall within seasons. Here a generalization of the Richardson model is adopted which has rainfall states (dry, light rain, and heavy rain) some of which are hidden or unobserved. It is further assumed that the rainfall states generate rainfall that is independent of season (seasonally invariant), so it is only the dynamics of the rainfall states that vary from season to season. A suitable estimation strategy based on maximum likelihood and the EM algorithm is developed for fitting the model across a region. This strategy is validated on simulated data. Various forms of the model are fitted to daily rainfall measurements from 12 sites in southern New Zealand. These results are discussed and compared to those from fitting standard fixed season models.
      PubDate: 2014-01-13T15:50:53.167954-05:
      DOI: 10.1002/2013WR014325
  • Quantifying streambed deposition and scour from stream and hyporheic water
           temperature time series
    • Authors: Daniele Tonina; Charles Luce, Frank Gariglio
      Pages: n/a - n/a
      Abstract: We propose a new method based on temperature time series of surface and streambed pore waters to monitor local changes in streambed surface elevations at a nominally daily time scale. The proposed method uses the naturally occurring daily temperature signal changes in amplitude and phase between stream water and the water flowing within the streambed sediment. Application of the method in a fine‐bedded stream predicts the timing and magnitude of a prescribed sequence of scour and deposition. This provides a new, effective, easy to use, and economic methodology to monitor the temporal evolution of erosion and depositional patterns in rivers.
      PubDate: 2014-01-13T15:44:21.783743-05:
      DOI: 10.1002/2013WR014567
  • Reply to comment by Henriette I. Jager and Ryan A. McManamay on
           “Cumulative biophysical impact of small and large hydropower
           development in Nu River, China”
    • Authors: Kelly M. Kibler; Desiree D. Tullos
      Pages: n/a - n/a
      PubDate: 2014-01-13T15:41:21.960817-05:
      DOI: 10.1002/2013WR014629
  • Hydrodynamic coupling in microbially mediated fracture mineralization:
           Formation of self‐organized groundwater flow channels
    • Authors: Gráinne El Mountassir; Rebecca J. Lunn, Heather Moir, Erica MacLachlan
      Pages: 1 - 16
      Abstract: Evidence of fossilized microorganisms embedded within mineral veins and mineral‐filled fractures has been observed in a wide range of geological environments. Microorganisms can act as sites for mineral nucleation and also contribute to mineral precipitation by inducing local geochemical changes. In this study, we explore fundamental controls on microbially induced mineralization in rock fractures. Specifically, we systematically investigate the influence of hydrodynamics (velocity, flow rate, and aperture) on microbially mediated calcite precipitation. Our experimental results demonstrate that a feedback mechanism exists between the gradual reduction in fracture aperture due to precipitation, and its effect on the local fluid velocity. This feedback results in mineral‐fill distributions that focus flow into a small number of self‐organizing channels that remain open, ultimately controlling the final aperture profile that governs flow within the fracture. This hydrodynamic coupling can explain field observations of discrete groundwater flow channeling within fracture‐fill mineral geometries where strong evidence of microbial activity is reported.
      PubDate: 2014-01-06T15:20:10.261681-05:
      DOI: 10.1002/2013WR013578
  • Drivers of the virtual water trade
    • Authors: S. Tamea; J. A. Carr, F. Laio, L. Ridolfi
      Pages: 17 - 28
      Abstract: Through the international trade of food commodities, countries virtually export or import the water used for food production, known as “virtual water.” The international trade network thus implies a network of virtual water flows from exporting to importing countries. The purpose of this study is to identify some controlling factors of the virtual water network by means of multivariate regression analyses, or gravity laws, as often named in economics. Starting from the FAOSTAT database, we reconstruct 25 years (1986–2010) of international virtual water trade values; we then analyze the dependence of the exchanged fluxes on: population, gross domestic product, arable land, virtual water embedded in agricultural production and dietary demand, and geographical distance between countries. Significant drivers are identified for each country considering separately export and import fluxes; temporal trends are outlined and the relative importance of drivers is assessed by a commonality analysis. Results indicate that population, gross domestic product and geographical distance are the major drivers of virtual water fluxes, with a minor (nonnegligible) contribution given by the agricultural production of exporting countries. Such drivers have become relevant for an increasing number of countries throughout the years, with an increasing variance explained by the distance between countries and a decreasing role of the gross domestic product. The worldwide adjusted coefficient of determination of fitted gravity‐law model is 0.57 (in 2010), and it has increased in time, confirming the good descriptive capability of selected drivers for the virtual water trade.
      PubDate: 2014-01-06T14:52:42.832119-05:
      DOI: 10.1002/2013WR014707
  • Motivational indictors predicting the engagement, frequency and adequacy
           of rainwater tank maintenance
    • Authors: Aditi Mankad; Murni Greenhill
      Pages: 29 - 38
      Abstract: Rainwater tank maintenance is a key social behavior in our changing environment, as tanks are being adopted worldwide to augment household water supplies and reduce urban water stress. The maintenance of rainwater tanks in urban areas is an important pro‐environmental behavior that prevents public health issues arising from unhygienic tank use. This study examined motivational differences in maintenance behavior between householders with retrofitted and mandated (compulsory) rainwater tanks on their property (N = 1988). Results showed that retrofitted tank owners were more self‐determined in their motivation than mandated owners. Amotivation and integrated regulation were both dominant predictors of engagement in tank maintenance, frequency and adequacy of tank maintenance activities. Those involved in more maintenance activity were likely driven to do so because of feelings of adherence to personal goals and values (e.g., as “sustainable” citizens), whereas individuals who experienced a lack of control and alienation from the activity were likely to view maintenance as meaningless. Thus, people with higher integrated regulation engaged in more tank maintenance activities, whereas more amotivated individuals engaged in less maintenance. As cities begin relying more on citizen self‐sufficiency with respect to water and energy resources, issues relating to infrastructure maintenance and operation become paramount. Results show that motivation is important in the impetus to engage in a pro‐environmental behavior as well as the frequency and accuracy with which that behavior is undertaken. Policy implications are further discussed.
      PubDate: 2014-01-06T15:12:19.745935-05:
      DOI: 10.1002/2013WR014338
  • Predicting natural channel patterns based on landscape and geomorphic
           controls in the Columbia River basin, USA
    • Authors: Tim Beechie; Hiroo Imaki
      Pages: 39 - 57
      Abstract: Based on known relationships of slope, discharge, valley confinement, sediment supply, and sediment caliber in controlling channel patterns, we developed multivariate models to predict natural channel patterns across the 674,500 km2 Columbia River basin, USA. We used readily available geospatial data sets to calculate reach slopes, 2 year flood discharge, and valley confinement, as well as to develop hypothesized landscape‐level surrogates for sediment load and caliber (relative slope, percent of drainage area in alpine terrain, and percent of drainage area in erosive fine‐grained lithologies). Using a support vector machine (SVM) classifier, we found that the four channel patterns were best distinguished by a model including all variables except valley confinement (82% overall accuracy). We then used that model to predict channel pattern for the entire basin and found that the spatial distribution of straight, meandering, anabranching, and braided patterns were consistent with regional topography and geology. A simple slope‐discharge model distinguished meandering channels from all other channel patterns, but did not clearly distinguish braided from straight channels (68% overall accuracy). Addition of one or more of the hypothesized sediment supply surrogates improved prediction accuracy by 4–14% over slope and discharge alone. Braided and straight channels were most clearly distinguished on an axis of relative slope, whereas braided and anabranching channels were most clearly distinguished by adding percent alpine area to the model.
      PubDate: 2014-01-07T13:24:01.533274-05:
      DOI: 10.1002/2013WR013629
  • A new model for coupled multicomponent NAPL dissolution and
           aqueous‐phase transport, with application to creosote dissolution in
           discrete fractures
    • Authors: Scott K. Hansen; Bernard H. Kueper
      Pages: 58 - 70
      Abstract: This paper concerns a new modeling approach to multicomponent NAPL dissolution and transport, based on analytic solutions and Laguerre series. This approach allows virtually any of the numerous existing 1‐D analytic transport solutions in the literature to be coupled with arbitrary boundary conditions stemming from nonlinear NAPL dissolution, as dictated by Raoult's Law. A computer implementation of this approach to coupled dissolution and transport in parallel fractures—which no other screening tool known to the authors covers—is presented. This is verified against an existing analytic transport solution that assumes a constant boundary condition. Subsequently, the model is demonstrated via a study of separation of PAH and phenolic plumes generated by dissolution of creosote, using the new computer implementation. The PAH and phenolic constituents of creosote strongly differ in both their dissolution and their transport behavior, and this is shown to necessitate the use of a tool that can account for both processes, such as the one developed here. We also find the possibility of PAH and phenolic plumes becoming entirely disjoint.
      PubDate: 2014-01-07T13:23:31.756846-05:
      DOI: 10.1002/2013WR013773
  • Hydraulic characterization of aquifers by thermal response testing:
           Validation by large‐scale tank and field experiments
    • Authors: Valentin Wagner; Peter Bayer, Gerhard Bisch, Markus Kübert, Philipp Blum
      Pages: 71 - 85
      Abstract: Thermal response tests (TRTs) are a common field method in shallow geothermics to estimate thermal properties of the ground. During the test, a constantly heated fluid is circulated in closed tubes within a vertical borehole heat exchanger (BHE). The observed temperature development of the fluid is characteristic for the thermal properties of the ground and the BHE. We show that, when the BHE is installed in an aquifer with significant horizontal groundwater flow, this test can also be used for hydrogeological characterization of the penetrated subsurface. An evaluation method based on the moving line source equation and considering the natural occurring variability of the thermal transport parameters is presented. It is validated by application to a well‐controlled, large‐scale tank experiment with 9 m length, 6 m width, and 4.5 m depth, and by data interpretation from a field‐scale test. The tank experiment imitates an advection‐influenced TRT in a well‐known layered aquifer. The field experiment was recorded with a 100 m deep BHE, installed in a gravel aquifer in southwest Germany. The evaluations of both experiments result in similar hydraulic conductivity ranges as determined by standard hydraulic investigation methods such as pumping tests and sieve analyses. Thus, advection‐influenced TRTs could also potentially be used to determine integral hydraulic conductivity of the subsurface.
      PubDate: 2014-01-07T13:27:54.269503-05:
      DOI: 10.1002/2013WR013939
  • Diel flow pulses drive particulate organic matter transport from microbial
           mats in a glacial meltwater stream in the McMurdo Dry Valleys
    • Authors: James D. S. Cullis; Lee F. Stanish, Diane M. McKnight
      Pages: 86 - 97
      Abstract: Many glacial meltwater streams in the McMurdo Dry Valleys (MDV) of Antarctica contain abundant microbial mats, representing hot spots of primary production in a barren landscape. These mats persist through the winter in a freeze‐dried state and grow in the summer, experiencing a dynamic hydrologic regime as streamflow varies on a diel cycle and with weather conditions. During diel peaks in flow these streams transport particulate organic matter (POM) to the downstream closed‐basin lakes. We investigated the spatial and temporal dynamics of POM transport derived from the scouring of microbial mats in Von Guerard Stream of the MDV. The results show clockwise hysteresis effects in POM concentration over diel flood pulses and suggests that POM transport in the MDVs is supply limited. Further studies are required to confirm this and to identify the potential contributing sources of POM. The hysteresis effect was modeled using an approach derived from models of sediment transport in streams. Spatial variations in POM transport indicate that patch‐scale variations in bed shear stress and benthic biomass also influence transport which is integrated downstream over several 100's of meters. Large variations in the POM transport dynamics between different diel flood pulses were found to be related to the time since a resetting flood event and the regrowth of potentially mobile benthic biomass, providing further evidence of the importance of supply limitation and flow variability in controlling the organic matter flux of stream ecosystems.
      PubDate: 2014-01-07T13:27:48.499633-05:
      DOI: 10.1002/2013WR014061
  • Seasonal precipitation patterns along pathways of South American
           low‐level jets and aerial rivers
    • Authors: Germán Poveda; Liliana Jaramillo, Luisa F. Vallejo
      Pages: 98 - 118
      Abstract: We study the seasonal dynamics of the eastern Pacific (CHOCO) and Caribbean low‐level jets (LLJ), and aerial rivers (AR) acting on tropical and subtropical South America. Using the ERA‐Interim reanalysis (1979–2012), we show that the convergence of both LLJs over the eastern Pacific‐western Colombia contributes to the explanation of the region's world‐record rainfall. Diverse variables involved in the transport and storage of moisture permit the identification of an AR over northern South America involving a midtropospheric easterly jet that connects the Atlantic and Pacific Oceans across the Andes, with stronger activity in April to August. Other major seasonal AR pathways constitute part of a large gyre originating over the tropical North Atlantic, veering to the southeast over the eastern Andes and reaching regions of northern Argentina and southeastern Brazil. We illustrate the distribution of average seasonal precipitation along the LLJs and AR pathways with data from the Tropical Rainfall Measuring Mission (1998–2011), combined with considerations of CAPE, topography, and land cover. In addition, the theory of the biotic pump of atmospheric moisture (BiPAM) is tested at seasonal time scales, and found to hold in 8 out of 12 ARs, and 22 out of 32 forest‐covered tracks (64% in distance) along the ARs. Deviations from BiPAM's predictions of rainfall distribution are explained by the effects of topography, orography, and land cover types different from forests. Our results lend a strong observational support to the BiPAM theory at seasonal time scales over South American forested flat lands.
      PubDate: 2014-01-07T15:26:58.348098-05:
      DOI: 10.1002/2013WR014087
  • A modeling approach to represent hysteresis in capillary
           pressure‐saturation relationship based on fluid connectivity in void
    • Authors: Abdullah Cihan; Jens Birkholzer, Tissa H. Illangasekare, Quanlin Zhou
      Pages: 119 - 131
      Abstract: This study presents a new model for description of hysteretic constitutive relationships between capillary pressure and saturation under capillary‐dominated multiphase flow conditions in porous media. Hysteretic relationships are required for accurate prediction of spatial and temporal distribution of multiphase fluids in response to successively occurring drainage and imbibition events in porous media. In addition to contact angle effects, connectivity of the void space in the porous medium plays a central role for the macroscopic manifestation of hysteresis behavior and capillary entrapment of wetting and nonwetting fluids. The hysteretic constitutive model developed in this work uses void‐size distribution and a measure of connectivity for void space to compute the hysteretic curves and to predict entrapped fluid‐phase saturations. Two functions, the drainage connectivity function and the wetting connectivity function, are introduced to characterize connectivity of fluids in void space during drainage and wetting processes. These functions can be estimated through pore‐scale simulations in computer‐generated porous media or from traditional experimental measurements of primary drainage and main wetting curves. The hysteresis model results are verified by comparing the model predicted scanning curves with 3‐D pore‐scale simulations as well as with actual data sets obtained from column experiments found in the literature.
      PubDate: 2014-01-08T14:30:42.264345-05:
      DOI: 10.1002/2013WR014280
  • Using a bias aware EnKF to account for unresolved structure in an
           unsaturated zone model
    • Authors: D. Erdal; I. Neuweiler, U. Wollschläger
      Pages: 132 - 147
      Abstract: When predicting flow in the unsaturated zone, any method for modeling the flow will have to define how, and to what level, the subsurface structure is resolved. In this paper, we use the Ensemble Kalman Filter to assimilate local soil water content observations from both a synthetic layered lysimeter and a real field experiment in layered soil in an unsaturated water flow model. We investigate the use of colored noise bias corrections to account for unresolved subsurface layering in a homogeneous model and compare this approach with a fully resolved model. In both models, we use a simplified model parameterization in the Ensemble Kalman Filter. The results show that the use of bias corrections can increase the predictive capability of a simplified homogeneous flow model if the bias corrections are applied to the model states. If correct knowledge of the layering structure is available, the fully resolved model performs best. However, if no, or erroneous, layering is used in the model, the use of a homogeneous model with bias corrections can be the better choice for modeling the behavior of the system.
      PubDate: 2014-01-08T12:18:16.110597-05:
      DOI: 10.1002/2012WR013443
  • Ecohydrological effects of management on subalpine grasslands: From local
           to catchment scale
    • Authors: Simone Fatichi; Matthias J. Zeeman, Jürg Fuhrer, Paolo Burlando
      Pages: 148 - 164
      Abstract: Grassland and pastures are important land uses in subalpine and alpine environments. They are typically subjected to management practices that can change the biophysical structure of the canopy through defoliation and can alter soil hydraulic properties. These modifications have the potential to impact hydrological and energy fluxes as well as the primary productivity of grasslands. We investigate how a series of management practices, such as grass cut, grazing, and the consequent soil compaction due to treading by animals are affecting water resources, flood generation, and grassland productivity in a subalpine region. Results are obtained using a mechanistic ecohydrological model, Tethys‐Chloris. The model is first confirmed using energy, water, and carbon fluxes measured at three eddy covariance stations over grasslands in Switzerland and discharge measured in a small experimental catchment. A series of virtual experiments are then designed to elucidate the importance of various management scenarios at the plot and catchment scales. Results show that only severe management actions such as low grass cuts or heavy grazing are able to influence considerably the long‐term hydrological behavior. Moderate management practices are typically unable to modify the system response in terms of energy and water fluxes. An important short‐term effect is represented by animal‐induced soil compaction that can reduce infiltration capacity leading to peak flow considerably higher than in undisturbed conditions. The productivity of vegetation in absence of nutrient limitation is considerably affected by the different management scenarios with tolerable disturbances that lead to higher aboveground net primary production.
      PubDate: 2014-01-08T14:30:55.623869-05:
      DOI: 10.1002/2013WR014535
  • Groundwater flow and salt transport in a subterranean estuary driven by
           intensified wave conditions
    • Authors: Clare Robinson; Pei Xin, Ling Li, D. A. Barry
      Pages: 165 - 181
      Abstract: A numerical study, based on a density‐dependent variably saturated groundwater flow model, was conducted to investigate flow and salt transport in a nearshore aquifer under intensified wave conditions caused by offshore storms. Temporally varying onshore hydraulic gradients due to wave setup were determined as the seaward boundary condition for the simulated aquifer. The results showed a rapid increase in influxes across the aquifer‐ocean interface in response to the wave event followed by a more gradual increase in effluxes. The upper saline plume first widened horizontally as the wave setup point moved landward. It then expanded vertically with recirculating seawater pushed downward by the wave‐induced hydraulic gradient. The time for the salt distribution to return to the prestorm condition was up to a hundred days and correlated strongly with the time for seawater to recirculate through the aquifer. The pathways of recirculating seawater and fresh groundwater were largely modified by the wave event. These pathways crossed through the same spatial locations at similar times, indicating significant salt‐freshwater mixing. The flow and salt transport dynamics were more responsive to wave events of longer duration and higher intensity, especially in more permeable aquifers with lower fresh groundwater discharge. Despite their larger response, aquifers with higher permeability and beach slope recovered more rapidly postevent. The rapid recovery of the flows compared with the salinity distribution should be considered in field data interpretation. Due to their long‐lasting impact, wave events may significantly influence the geochemical conditions and the fate of chemicals in a subterranean estuary.
      PubDate: 2014-01-08T14:35:44.58761-05:0
      DOI: 10.1002/2013WR013813
  • Probabilistic postprocessing models for flow forecasts for a system of
           catchments and several lead times
    • Authors: K. Engeland; I. Steinsland
      Pages: 182 - 197
      Abstract: This paper introduces a methodology for the construction of probabilistic inflow forecasts for multiple catchments and lead times. A postprocessing approach is used, and a Gaussian model is applied for transformed variables. In operational situations, it is a straightforward task to use the models to sample inflow ensembles which inherit the dependencies between catchments and lead times. The methodology was tested and demonstrated in the river systems linked to the Ulla‐Førre hydropower complex in southern Norway, where simultaneous probabilistic forecasts for five catchments and ten lead times were constructed. The methodology exhibits sufficient flexibility to utilize deterministic flow forecasts from a numerical hydrological model as well as statistical forecasts such as persistent forecasts and sliding window climatology forecasts. It also deals with variation in the relative weights of these forecasts with both catchment and lead time. When evaluating predictive performance in original space using cross‐validation, the case study found that it is important to include the persistent forecast for the initial lead times and the hydrological forecast for medium‐term lead times. Sliding window climatology forecasts become more important for the latest lead times. Furthermore, operationally important features in this case study such as heteroscedasticity, lead time varying between lead time dependency and lead time varying between catchment dependency are captured.
      PubDate: 2014-01-08T12:18:04.556164-05:
      DOI: 10.1002/2012WR012757
  • Fast iterative implementation of large‐scale nonlinear
           geostatistical inverse modeling
    • Authors: Xiaoyi Liu; Quanlin Zhou, Peter K. Kitanidis, Jens T. Birkholzer
      Pages: 198 - 207
      Abstract: In nonlinear geostatistical inverse problems, it often takes a significant amount of computational cost to form linear geostatistical inversion systems by linearizing the forward model. More specifically, the storage cost associated with the sensitivity matrix H (m × n, where m and n are the numbers of measurements and unknowns, respectively) is high, especially when both m and n are large in for instance, 3‐D tomography problems. In this research, instead of explicitly forming and directly solving the linear geostatistical inversion system, we use MINRES, a Krylov subspace method, to solve it iteratively. During each iteration in MINRES, we only compute the products Hx and HTx for any appropriately sized vectors x, for which we solve the forward problem twice. As a result, we reduce the memory requirement from O(mn) to O(m)+O(n). This iterative methodology is combined with the Bayesian inverse method in Kitanidis (1996) to solve large‐scale inversion problems. The computational advantages of our methodology are demonstrated using a large‐scale 3‐D numerical hydraulic tomography problem with transient pressure measurements (250,000 unknowns and ∼100,000 measurements). In this case, ∼200 GB of memory would otherwise be required to fully compute and store the sensitivity matrix H at each Newton step during optimization. The CPU cost can also be significantly reduced in terms of the total number of forward simulations. In the end, we discuss potential extension of the methodology to other geostatistical methods such as the Successive Linear Estimator.
      PubDate: 2014-01-08T10:13:03.444219-05:
      DOI: 10.1002/2012WR013241
  • Evaluating the performance of parallel subsurface simulators: An
           illustrative example with PFLOTRAN
    • Authors: G. E. Hammond; P. C. Lichtner, R. T. Mills
      Pages: 208 - 228
      Abstract: To better inform the subsurface scientist on the expected performance of parallel simulators, this work investigates performance of the reactive multiphase flow and multicomponent biogeochemical transport code PFLOTRAN as it is applied to several realistic modeling scenarios run on the Jaguar supercomputer. After a brief introduction to the code's parallel layout and code design, PFLOTRAN's parallel performance (measured through strong and weak scalability analyses) is evaluated in the context of conceptual model layout, software and algorithmic design, and known hardware limitations. PFLOTRAN scales well (with regard to strong scaling) for three realistic problem scenarios: (1) in situ leaching of copper from a mineral ore deposit within a 5‐spot flow regime, (2) transient flow and solute transport within a regional doublet, and (3) a real‐world problem involving uranium surface complexation within a heterogeneous and extremely dynamic variably saturated flow field. Weak scalability is discussed in detail for the regional doublet problem, and several difficulties with its interpretation are noted.
      PubDate: 2014-01-08T14:30:48.704795-05:
      DOI: 10.1002/2012WR013483
  • Modeling the flow resistance of woody vegetation using physically based
           properties of the foliage and stem
    • Authors: Kaisa Västilä; Juha Järvelä
      Pages: 229 - 245
      Abstract: Both the foliage and stem essentially influence the flow resistance of woody plants, but their different biomechanical properties complicate the parameterization of foliated vegetation for modeling. This paper investigates whether modeling of flow resistance caused by natural woody vegetation can be improved using explicit description of both the foliage and stem. For this purpose, we directly measured the drag forces of Alnus glutinosa, Betula pendula, Salix viminalis, and Salix x rubens twigs in a laboratory flume at four foliation levels, parameterized with the leaf‐area‐to‐stem‐area ratio AL/AS. The species differed in the foliage drag but had approximately equal stem drag. For the foliated twigs, increasing AL/AS was found to increase the reconfiguration and the share of the foliage drag to the total drag. The experiments provided new insight into the factors governing the flow resistance of natural woody vegetation and allowed us to develop a model for estimating the vegetative friction factor using the linear superposition of the foliage and stem drag. The model is novel in that the foliage and stem are separately described with physically based parameters: drag coefficients, reconfiguration parameters, and leaf area and frontal‐projected stem area per ground area. The model could satisfactorily predict the flow resistance of twig to sapling‐sized specimens of the investigated species at velocities of 0.05–1 m/s. As a further benefit, the model allows exploring the variability in drag and reconfiguration associated with differing abundance of the foliage in relation to the stem.
      PubDate: 2014-01-10T16:00:53.024202-05:
      DOI: 10.1002/2013WR013819
  • Groundwater remediation using the information gap decision theory
    • Authors: D. O'Malley; V. V. Vesselinov
      Pages: 246 - 256
      Abstract: One of the challenges in the design and selection of remediation activities for subsurface contamination is dealing with manifold uncertainties. A scientifically defensible decision process demands consideration of the uncertainties involved. A nonprobabilistic approach based on information gap (info‐gap) decision theory is employed to study the robustness of alternative remediation activities. This approach incorporates both parametric and nonparametric (conceptual) uncertainty in predicting contaminant concentrations that are effected by natural processes and the remediation activities. Two remedial scenarios are explored to demonstrate the applicability of the info‐gap approach to decision making related to groundwater remediation.
      PubDate: 2014-01-10T15:50:11.608276-05:
      DOI: 10.1002/2013WR014718
  • Estimation of evapotranspiration using diurnal groundwater level
           fluctuations: Comparison of different approaches with groundwater
           lysimeter data
    • Authors: Marcus Fahle; Ottfried Dietrich
      Pages: 273 - 286
      Abstract: In wetlands or riparian areas, water withdrawal by plants with access to groundwater or the capillary fringe often causes diurnal groundwater fluctuations. Various approaches use the characteristics of these fluctuations for estimation of daily groundwater evapotranspiration rates. The objective of this paper was to review the available methods, compare them with measured evapotranspiration and assess their recharge assumptions. For this purpose, we employed data of 85 rain‐free days of a weighable groundwater lysimeter situated at a grassland site in the Spreewald wetland in north‐east Germany. Measurements of hourly recharge and daily evapotranspiration rates were used to assess the different approaches. Our results showed that a maximum of 50% of the day to day variance of the daily evapotranspiration rates could be explained by the approaches based on groundwater fluctuations. Simple and more complex methods performed similarly. For some of the approaches, there were indications that erroneous assumptions compensated each other (e.g., when overestimated recharge counteracted underestimated storage change). We found that the usage of longer time spans resulted in improved estimates of the daily recharge rates and that the estimates were further enhanced by including two night averages. When derived from fitting estimates of recharge or evapotranspiration with according measurements the specific yield, needed to convert changes in water level to water volumes, differed considerably among the methods (from 0.022 to 0.064). Thus, the specific yield can be seen as “correction factor” that compensates for inadequate process descriptions.
      PubDate: 2014-01-13T12:16:10.337797-05:
      DOI: 10.1002/2013WR014472
  • Stochastic downscaling of precipitation to high‐resolution scenarios
           in orographically complex regions: 1. Model evaluation
    • Authors: R. Bordoy; P. Burlando
      Pages: 540 - 561
      Abstract: The simulation of space‐time precipitation has been studied since the late 1980s. However, there are still many open issues concerning the most appropriate approach to simulate it, specially in highly heterogeneous areas, such as in mountain environments. For this reason, we present here a comprehensive investigation of the Space‐Time Neyman‐Scott Rectangular Pulses model, with the purpose of analyzing its performance in a challenging Alpine environment of Switzerland and identifying weaknesses that can drive future improvements. The results point at the suitability of the model in reproducing not only the basic statistics at different temporal aggregations, but also the more challenging distributional and scaling properties. The intrinsic stationarity of the model in space, induced by the parameter estimation procedure, poses occasional limitations with regard to the accurate simulation of the variability of the observed climate characteristics, which are strongly influenced by local microclimates. However, the model is able, even in the complex Alpine environment, to preserve the spatial patterns observed in the actual precipitation process. The study allowed (i) to conclude about the robustness of the model and its suitability for multisite downscaling of precipitation estimated from climate model simulations, as reported in the companion paper, and (ii) to put in evidence some limitations that require further consideration to improve space‐time rainfall generation.
      PubDate: 2014-01-27T15:00:21.831855-05:
      DOI: 10.1002/2012WR013289
  • Stochastic downscaling of climate model precipitation outputs in
           orographically complex regions: 2. Downscaling methodology
    • Authors: R. Bordoy; P. Burlando
      Pages: 562 - 579
      Abstract: A new methodology of stochastic downscaling of climate model precipitation outputs to subdaily temporal resolution and in a multisite framework is presented. The methodology is based on the reparameterization for future climate of the Spatiotemporal Neyman‐Scott Rectangular Pulses model. The reparameterization is carried out by estimating the model parameters as done for the calibration of the model for the historical climate and using future statistics that are obtained: (i) applying to the daily historical statistics a factor of change computed from the control and future climate model outputs and (ii) by rescaling the altered daily statistics according to the scaling properties exhibited by the historical raw moments, in order to generate the future statistics at the temporal resolutions required by the reparameterization procedure. The downscaled scenarios are obtained in a multisite framework accounting for cross correlations among the stations. The methodology represents a robust, efficient, and unique approach to generate multiple series of spatially distributed subdaily precipitation scenarios by Monte Carlo simulation. It presents thus a unique alternative for addressing the internal variability of the precipitation process at high temporal and spatial resolution, as compared to other downscaling techniques, which are affected by both computational and resolution problems. The application of the presented approach is demonstrated for a region of complex orography where the model has proved to provide good results, in order to analyze potential changes in such vulnerable areas.
      PubDate: 2014-01-27T15:00:34.074128-05:
      DOI: 10.1002/wrcr.20443
  • A copula‐based precipitation forecasting model: Investigating the
           interdecadal modulation of ENSO's impacts on monthly precipitation
    • Authors: C. Prakash Khedun; Ashok K. Mishra, Vijay P. Singh, John R. Giardino
      Pages: 580 - 600
      Abstract: The influence of two large‐scale circulation patterns (the El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO)), and the effect of the interdecadal modulation of ENSO on precipitation in the state of Texas, U.S., was explored. Texas, by virtue of its size, topography, and geographical location, spans a wide range of climatic regions. The state is divided into 10 climate divisions. The precipitation pattern in each division follows different probability distributions. The climate regimes which trigger this difference are discussed. The seasonal correlation between ENSO and PDO with precipitation anomaly in each climate division was established. Copula‐based models were developed to examine the dependence structure between the large‐scale climate indices and average monthly seasonal precipitation. The choice of copula is discussed in light of the dependence structure. The selected copulas were then used to simulate precipitation anomalies in three climate divisions: one which has a semiarid climate, one located in the wettest region, and one straddling the subtropical humid and subtropical subhumid regions of the state. The statistical performance of bivariate models for ENSO and precipitation, and trivariate models for ENSO, PDO, and precipitation, in simulating precipitation anomalies were compared. In general, inclusion of PDO was found to improve simulation results. The most notable improvement was in simulating negative precipitation anomalies during La Niña and negative PDO. The copula models were also tested for their abilities to predict precipitation anomalies in these three regions. Again, the trivariate models performed better, especially in predicting droughts due to La Niña and negative PDO.
      PubDate: 2014-01-27T16:33:47.531121-05:
      DOI: 10.1002/2013WR013763
  • Modeling the relationship between climate oscillations and drought by a
           multivariate GARCH model
    • Authors: R. Modarres; T. B. M. J. Ouarda
      Pages: 601 - 618
      Abstract: Typical multivariate time series models may exhibit comovement in mean but not in variance of hydrologic and climatic variables. This paper introduces multivariate generalized autoregressive conditional heteroscedasticity (GARCH) models to capture the comovement of the variance or the conditional covariance between two hydroclimatic time series. The diagonal vectorized and Baba‐Engle‐Kroft‐Kroner models are developed to evaluate the covariance between drought and two atmospheric circulations, Southern Oscillation Index (SOI) and North Atlantic Oscillation (NAO) time series during 1954–2000. The univariate generalized autoregressive conditional heteroscedasticity model indicates a strong persistency level in conditional variance for NAO and a moderate persistency level for SOI. The conditional variance of short‐term drought index indicates low level of persistency, while the long‐term index drought indicates high level of persistency in conditional variance. The estimated conditional covariance between drought and atmospheric indices is shown to be weak and negative. It is also observed that the covariance between drought and atmospheric indices is largely dependent on short‐run variance of atmospheric indices rather than their long‐run variance. The nonlinearity and stationarity tests show that the conditional covariances are nonlinear but stationary. However, the degree of nonlinearity is higher for the covariance between long‐term drought and atmospheric indices. It is also observed that the nonlinearity of NAO is higher than that for SOI, in contrast to the stationarity which is stronger for SOI time series.
      PubDate: 2014-01-27T14:56:04.487207-05:
      DOI: 10.1002/2013WR013810
  • Flooding dynamics on the lower Amazon floodplain: 1. Hydraulic controls on
           water elevation, inundation extent, and river‐floodplain discharge
    • Authors: Conrado M. Rudorff; John M. Melack, Paul D. Bates
      Pages: 619 - 634
      Abstract: Modeling the routing of flood waters across large floodplains is challenging because flows respond to dynamic hydraulic controls from complex geomorphology, vegetation, and multiple water sources. In this study, we analyzed the topographic and hydrologic controls of inundation dynamics of a large floodplain unit (2440 km2) along the lower Amazon River. We combined land topography derived from the Shuttle Radar Topography Mission (SRTM) with underwater topography derived from an extensive echo‐sounding survey to generate a seamless digital elevation model (DEM). Floodplain inundation was simulated using LISFLOOD‐FP, which combines one‐dimensional river routing with two‐dimensional overland flow, and a local hydrological model. For the first time, accurate simulation of filling and drainage of an Amazon floodplain was achieved with quantification of changes in water elevation, flooding extent, and river‐floodplain exchange. We examined the role of diffuse overbank versus channelized flows on river‐floodplain exchange. Diffuse overbank flows represent 93% of total river to floodplain discharge and 54% of floodplain to river discharge. Floodplain discharge during high‐water was four times higher than field observation values when the SRTM v.4 DEM with no correction was used for simulation because of a −4.4 m elevation bias originating from residual motion errors of the SRTM interferometric baseline.
      PubDate: 2014-01-27T16:18:24.126514-05:
      DOI: 10.1002/2013WR014091
  • Flooding dynamics on the lower Amazon floodplain: 2. Seasonal and
           interannual hydrological variability
    • Authors: Conrado M. Rudorff; John M. Melack, Paul D. Bates
      Pages: 635 - 649
      Abstract: We analyzed seasonal and interannual variability in hydrological fluxes and inundation dynamics of a large floodplain unit (2440 km2) along the lower Amazon River over a period of 15 years (1995–2010). Floodplain inundation was simulated using LISFLOOD‐FP, which combines one‐dimensional river routing with two‐dimensional overland flow, and a local hydrological model. Dominant sources of inflow varied seasonally among direct rain and local runoff (November), Amazon River (December to August) and seepage (September and October). Shifts in timing of dominance among the water balance components occurred conform variations in annual peak stage. The period of dominance of river inflow over total floodplain influxes began about 1 month earlier and ended 1 month later in the 2009 high flood year compared to the 1998 low flood year. On average, river to floodplain discharge represented 0.75% of the Amazon River discharge at Óbidos and 82% of the annual hydrological influxes to the floodplain. We observed an up to ninefold variation in river‐floodplain annual discharge. Relatively small increments in main stem peak discharge cause disproportionately large changes in the flow routed through the floodplain. Despite the higher frequency of years with lower minimum stages, the intensification of the hydrological cycle of the Amazon Basin is causing substantially greater amounts of riverine water to flow across floodplain environments.
      PubDate: 2014-01-27T16:24:31.45587-05:0
      DOI: 10.1002/2013WR014714
  • An information theoretic alternative to model a natural system using
           observational information alone
    • Authors: Ashish Sharma; Raj Mehrotra
      Pages: 650 - 660
      Abstract: How to define a system? This is a problem faced routinely in science and engineering, with solutions developed from our understanding of the processes inherent, to assessing the underlying structure based on observational evidence alone. In general, system specification involves identifying a few meaningful predictors (from a large enough set that is plausibly related to the response) and formulating a relation between them and the system response being modeled. For systems where physical relationships are less apparent, and sufficient observational records exist, a range of statistical alternatives have been investigated as a possible way of specifying the underlying form. Here we introduce partial information (PI) as a new means for specifying the system, its key advantage being the relative lack of major assumptions about the processes being modeled in order to characterize the complete system. In addition to PI which offers a means of identifying the system predictors of interest, we also introduce the concept of partial weights (PWs) which uses the identified predictors to formulate a predictive model that acknowledges the relative contributions, predictor variables make to the prediction of the response. We assess the utility of the PI‐PW framework using synthetically generated data sets from known linear, nonlinear, and high‐dimensional dynamic yet chaotic systems and demonstrate the efficacy of the procedure in ascertaining the underlying true system with varying extents of observational evidence available. We highlight how this framework can be invaluable in formulating prediction models for natural systems which are modeled using empirical or semiempirical alternatives and discuss current limitations that still need to be overcome.
      PubDate: 2014-01-27T15:33:47.403644-05:
      DOI: 10.1002/2013WR013845
  • Study of the effect of wind speed on evaporation from soil through
           integrated modeling of the atmospheric boundary layer and shallow
    • Authors: Hossein Davarzani; Kathleen Smits, Ryan M. Tolene, Tissa Illangasekare
      Pages: 661 - 680
      Abstract: In an effort to develop methods based on integrating the subsurface to the atmospheric boundary layer to estimate evaporation, we developed a model based on the coupling of Navier‐Stokes free flow and Darcy flow in porous medium. The model was tested using experimental data to study the effect of wind speed on evaporation. The model consists of the coupled equations of mass conservation for two‐phase flow in porous medium with single‐phase flow in the free‐flow domain under nonisothermal, nonequilibrium phase change conditions. In this model, the evaporation rate and soil surface temperature and relative humidity at the interface come directly from the integrated model output. To experimentally validate numerical results, we developed a unique test system consisting of a wind tunnel interfaced with a soil tank instrumented with a network of sensors to measure soil‐water variables. Results demonstrated that, by using this coupling approach, it is possible to predict the different stages of the drying process with good accuracy. Increasing the wind speed increases the first stage evaporation rate and decreases the transition time between two evaporative stages (soil water flow to vapor diffusion controlled) at low velocity values; then, at high wind speeds the evaporation rate becomes less dependent on the wind speed. On the contrary, the impact of wind speed on second stage evaporation (diffusion‐dominant stage) is not significant. We found that the thermal and solute dispersion in free‐flow systems has a significant influence on drying processes from porous media and should be taken into account.
      PubDate: 2014-01-27T16:08:02.018794-05:
      DOI: 10.1002/2013WR013952
  • A comparison between simulation and experiment for hysteretic phenomena
           during two‐phase immiscible displacement
    • Authors: F. Doster; R. Hilfer
      Pages: 681 - 686
      Abstract: The paper compares a theory for immiscible displacement based on distinguishing percolating and nonpercolating fluid parts with experimental observations from multistep outflow experiments. The theory was published in 2006 in Physica A, volume 371, pages 209–225; the experiments were published in 1991 in Water Resources Research, volume 27, pages 2113. The present paper focuses on hysteretic phenomena resulting from repeated cycling between drainage and imbibition processes in multistep pressure experiments. Taking into account, the hydraulic differences between percolating and nonpercolating fluid parts provides a physical basis to predict quantitatively the hysteretic phenomena observed in the experiment. While standard hysteretic extensions of the traditional theory are nonlocal in time the theory used in this paper is local in time. Instead of storing the pressure and saturation history, it requires only the current state of the system to reach the same quantitative agreement.
      PubDate: 2014-01-28T15:32:56.199858-05:
      DOI: 10.1002/2013WR014619
  • Calibrating a large‐extent high‐resolution coupled
           groundwater‐land surface model using soil moisture and discharge
    • Authors: E. H. Sutanudjaja; L. P. H. van Beek, S. M. de Jong, F. C. van Geer, M. F. P. Bierkens
      Pages: 687 - 705
      Abstract: We explore the possibility of using remotely sensed soil moisture data and in situ discharge observations to calibrate a large‐extent hydrological model. The model used is PCR‐GLOBWB‐MOD, which is a physically based and fully coupled groundwater‐land surface model operating at a daily basis and having a resolution of 30 arc sec (about 1 km at the equator). As a test bed, we use the combined Rhine‐Meuse basin (total area: about 200,000 km2), where there are 4250 point‐scale observed groundwater head time series that are used to verify the model results. Calibration is performed by simulating 3045 model runs with varying parameter values affecting groundwater head dynamics. The simulation results of all runs are evaluated against the remotely sensed soil moisture time series of SWI (Soil Water Index) and field discharge data. The former is derived from European Remote Sensing scatterometers and provides estimates of the first meter profile soil moisture content at 30 arc min resolution (50 km at the equator). From the evaluation of these runs, we then introduce a stepwise calibration approach that considers stream discharge first, then soil moisture, and finally verify the resulting simulation to groundwater head observations. Our results indicate that the remotely sensed soil moisture data can be used for the calibration of upper soil hydraulic conductivities determining simulated groundwater recharge of the model. However, discharge data should be included to obtain full calibration of the coupled model, specifically to constrain aquifer transmissivities and runoff‐infiltration partitioning processes. The stepwise approach introduced in this study, using both discharge and soil moisture data, can calibrate both discharge and soil moisture, as well as predicting groundwater head dynamics with acceptable accuracy. As our approach to parameterize and calibrate the model uses globally available data sets only, it opens up the possibility to set up large‐extent coupled groundwater‐land surface models in other basins or even globally.
      PubDate: 2014-01-28T15:47:19.378126-05:
      DOI: 10.1002/2013WR013807
  • Parameter estimation of a physically based land surface hydrologic model
           using the ensemble Kalman filter: A synthetic experiment
    • Authors: Yuning Shi; Kenneth J. Davis, Fuqing Zhang, Christopher J. Duffy, Xuan Yu
      Pages: 706 - 724
      Abstract: This paper presents multiple parameter estimation using multivariate observations via the ensemble Kalman filter (EnKF) for a physically based land surface hydrologic model. A data assimilation system is developed for a coupled physically based land surface hydrologic model (Flux‐PIHM) by incorporating EnKF for model parameter and state estimation. Synthetic data experiments are performed at a first‐order watershed, the Shale Hills watershed (0.08 km2). Six model parameters are estimated. Observations of discharge, water table depth, soil moisture, land surface temperature, sensible and latent heat fluxes, and transpiration are assimilated into the system. The results show that, given a limited number of site‐specific observations, the EnKF can be used to estimate Flux‐PIHM model parameters. All the estimated parameter values are very close to their true values, with the true values inside the estimated uncertainty range (1 standard deviation spread). The estimated parameter values are not affected by the initial guesses. It is found that discharge, soil moisture, and land surface temperature (or sensible and latent heat fluxes) are the most critical observations for the estimation of those six model parameters. The assimilation of multivariate observations applies strong constraints to parameter estimation, and provides unique parameter solutions. Model results reveal strong interaction between the van Genuchten parameters α and β, and between land surface and subsurface parameters. The EnKF data assimilation system provides a new approach for physically based hydrologic model calibration using multivariate observations. It can be used to provide guidance for observational system designs, and is promising for real‐time probabilistic flood and drought forecasting.
      PubDate: 2014-01-29T14:55:01.575659-05:
      DOI: 10.1002/2013WR014070
  • An estimate of energy dissipation due to soil‐moisture hysteresis
    • Authors: H. McNamara
      Pages: 725 - 735
      Abstract: Processes of infiltration, transport, and outflow in unsaturated soil necessarily involve the dissipation of energy through various processes. Accounting for these energetic processes can contribute to modeling hydrological and ecological systems. The well‐documented hysteretic relationship between matric potential and moisture content in soil suggests that one such mechanism of energy dissipation is associated with the cycling between wetting and drying processes, but it is challenging to estimate the magnitude of the effect in situ. The Preisach model, a generalization of the Independent Domain model, allows hysteresis effects to be incorporated into dynamical systems of differential equations. Building on earlier work using such systems with field data from the south‐west of Ireland, this work estimates the average rate of hysteretic energy dissipation. Through some straightforward assumptions, the magnitude of this rate is found to be of O(10−5) W m−3.
      PubDate: 2014-01-29T14:32:56.452358-05:
      DOI: 10.1002/2012WR012634
  • Analytical solution for capture and catchment zones of a well located on a
           groundwater divide
    • Authors: Florimond Smedt
      Pages: 736 - 740
      Abstract: An analytical solution is presented for capture and catchment zones of a well located on a groundwater divide in a recharged aquifer. The analytical solution is derived for a homogeneous, isotropic, and uniformly thick leaky aquifer. It is shown that streamlines and well‐catchment area have elongated shapes tending to infinity along the groundwater divide, and do not depend on any aquifer property, but only on the ratio of the well‐pumping rate and aquifer recharge flux. Isochrones delineating capture zones also depend on the mean residence time of the groundwater, which is independent of the well‐pumping rate. The capture and catchment zones differ significantly in both size and shape from the classical theory that ignores recharge. In particular, the catchment zone is wider and has a finite extent.
      PubDate: 2014-01-08T15:53:20.752983-05:
      DOI: 10.1002/2013WR014763
  • Flow in horizontally anisotropic multilayered aquifer systems with leaky
           wells and aquitards
    • Authors: Abdullah Cihan; Quanlin Zhou, Jens T. Birkholzer, Stephen R. Kraemer
      Pages: 741 - 747
      Abstract: Flow problems in an anisotropic domain can be transformed into ones in an equivalent isotropic domain by coordinate transformations. Once analytical solutions are obtained for the equivalent isotropic domain, they can be back transformed to the original anisotropic domain. The existing solutions presented by Cihan et al. (2011) for isotropic multilayered aquifer systems with alternating aquitards and multiple injection/pumping wells and leaky wells were modified to account for horizontal anisotropy in aquifers. The modified solutions for pressure buildup distribution and leakage rates through leaky wells can be used when the anisotropy direction and ratio ( Kx/Ky) are assumed to be identical for all aquifers alternating with aquitards. However, for multilayered aquifers alternating with aquicludes, both the principal direction of the anisotropic horizontal conductivity and the anisotropy ratio can be different in each aquifer. With coordinate transformation, a circular well with finite radius becomes an ellipse, and thus in the transformed domain the head contours in the immediate vicinity of the well have elliptical shapes. Through a radial flow approximation around the finite radius wells, the elliptical well boundaries in the transformed domain are approximated by an effective well radius expression. The analytical solutions with the effective radius approximations were compared with exact solutions as well as a numerical solution for elliptic flow. The effective well radius approximation is sufficiently accurate to predict the head buildup at the well bore of the injection/pumping wells for moderately anisotropic systems ( Kx/Ky≤25). The effective radius approximation gives satisfactory results for predicting head buildup at observation points and leakage through leaky wells away from the injection/pumping wells even for highly anisotropic aquifer systems (Kx/Ky≤1000).
      PubDate: 2014-01-10T16:03:36.551699-05:
      DOI: 10.1002/2013WR013867
  • Comment on “Groundwater depletion in the Middle East from GRACE with
           implications for transboundary water management in the
           Tigris‐Euphrates‐Western Iran Region” by Katalyn A. Voss
           et al.
    • Authors: Yakup Darama
      Pages: 754 - 757
      PubDate: 2014-01-13T12:15:31.386241-05:
      DOI: 10.1002/2013WR014084
  • Comment on “Cumulative biophysical impact of small and large
           hydropower development in Nu River, China” by Kelly M. Kibler and
           Desiree D. Tullos
    • Authors: Henriette I. Jager; Ryan A. McManamay
      Pages: 758 - 759
      PubDate: 2014-01-13T15:40:28.157462-05:
      DOI: 10.1002/2013WR014378
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