bluuebunny/crossref_metadata_2025 huggingface dataset:
Future directions for hydropedology: quantifying impacts of global change on land use
Authors: Vepraskas M. J. , Heitman J. L. , Austin R. E.
Published: April 2010

Abstract. Hydropedology is well positioned to address contemporary issues resulting from climate change. We propose a six step process by which digital, field-scale maps will be produced to show where climate change impacts will be greatest for two land uses: a) home sites using septic systems, and b) wetlands. State and federal laws have defined critical water table levels that can be used to determine where septic systems will function well or fail, and where wetlands are likely to occur. Hydrologic models along with historic rainfall and temperature data can be used to compute long records of water table data. However, it is difficult to extrapolate such data across land regions, because too little work has been done to test different ways for doing this reliably. The modeled water table data can be used to define soil drainage classes for individual mapping units, and the drainage classes used to extrapolate the data regionally using existing digital soil survey maps. Estimates of changes in precipitation and temperature can also be input into the models to compute changes to water table levels and drainage classes. To do this effectively, more work needs to be done on developing daily climate files from the monthly climate change predictions. Technology currently exists to use the NRCS Soil Survey Geographic (SSURGO) Database with hydrologic model predictions to develop maps within a GIS that show climate change impacts on septic system performance and wetland boundaries. By using these maps, planners will have the option to scale back development in sensitive areas, or simply monitor the water quality of these areas for pathogenic organisms. The calibrated models and prediction maps should be useful throughout the Coastal Plain region. Similar work for other climate-change and land-use issues can be a valuable contribution from hydropedologists.
EAGLE 2006 – multi-purpose, multi-angle and multi-sensor in-situ, airborne and space borne campaigns over grassland and forest
Authors: Su Z. , Timmermans W. J. , van der Tol C. , Dost R. J. J. , Bianchi R. , Gómez J. A. , House A. , Hajnsek I. , Menenti M. , Magliulo V. , Esposito M. , Haarbrink R. , Bosveld F. C. , Rothe R. , Baltink H. K. , Vekerdy Z. , Sobrino J. A. , Timmermans J. , van Laake P. , Salama S. , van der Kwast H. , Claassen E. , Stolk A. , Jia L. , Moors E. , Hartogensis O. , Gillespie A.
Published: April 2010

Abstract. EAGLE2006 – an intensive field campaign for the advances in land surface hydrometeorological processes – was carried out in the Netherlands from 8 to 18 June 2006, involving 16 institutions with in total 67 people from 16 different countries. In addition to the acquisition of multi-angle and multi-sensor satellite data, several airborne instruments – an optical imaging sensor, an imaging microwave radiometer, and a flux airplane – were deployed and extensive ground measurements were conducted over one grassland site at Cabauw and two forest sites at Loobos and Speulderbos in the central part of the Netherlands. The generated data set is both unique and urgently needed for the development and validation of models and inversion algorithms for quantitative land surface parameter estimation and land surface hydrometeorological process studies. EAGLE2006 was led by the Department of Water Resources of the International Institute for Geo-Information Science and Earth Observation (ITC) and originated from the combination of a number of initiatives supported by different funding agencies. The objectives of the EAGLE2006 campaign were closely related to the objectives of other European Space Agency (ESA) campaign activities (SPARC2004, SEN2FLEX2005 and especially AGRISAR2006). However, one important objective of the EAGLE 2006 campaign is to build up a data base for the investigation and validation of the retrieval of bio-geophysical parameters, obtained at different radar frequencies (X-, C- and L-Band) and at hyperspectral optical and thermal bands acquired simultaneously over contrasting vegetated fields (forest and grassland). As such, all activities were related to algorithm development for future satellite missions such as the Sentinels and for validation of retrievals of land surface parameters with optical and thermal and microwave sensors onboard current and future satellite missions. This contribution describes the campaign objectives and provides an overview of the airborne and field campaign dataset. This dataset is available for scientific investigations and can be accessed on the ESA Principal Investigator Portal http://eopi.esa.int.
Conditioning rainfall-runoff model parameters for ungauged catchments and land management impacts analysis
Authors: Bulygina N. , McIntyre N. , Wheater H.
Published: April 2010

Abstract. Data scarcity and model over-parameterisation, leading to model equifinality and large prediction uncertainty, are common barriers to effective hydrological modelling. The problem can be alleviated by constraining the prior parameter space using parameter regionalization. A common basis for regionalization in the UK is the HOST database which provides estimates of hydrological indices for different soil classifications. In our study, Base Flow Index is estimated from the HOST database and the power of this index for constraining the parameter space is explored. The method is applied to a highly discretized distributed model of a 12.5 km2 upland catchment in Wales. To assess probabilistic predictions against flow observations, a probabilistic version of the Nash-Sutcliffe efficiency is derived. For six flow gauges with reliable data, this efficiency ranged between 0.70 and 0.81, and inspection of the results shows that the model explains the data well. Knowledge of how Base Flow Index and interception losses may change under future land use management interventions was then used to further condition the model. Two interventions are considered: afforestation of grazed areas, and soil degradation associated with increased grazing intensity. Afforestation leads to median reduction in modelled runoff volume of 24% over the simulated 3 month period; and a median peak flow reduction ranging from 12–15% over the six gauges for the largest simulated event. Uncertainty in all results is suprisingly low and it is concluded that using Base Flow Index estimated from HOST is a simple and potentially powerful method of conditioning the parameter space under current and future land management.
Footprint issues in scintillometry over heterogeneous landscapes
Authors: Timmermans W. J. , Su Z. , Olioso A.
Published: April 2010

Abstract. Scintillometry is widely recognized as a potential tool for obtaining spatially aggregated sensible heat fluxes. Although many investigations have been made over contrasting component surfaces, few aggregation schemes consider footprint contributions. In this paper an approach is presented to infer average sensible heat flux over a very heterogeneous landscape by using a large aperture scintillometer. The methodology is demonstrated on simulated data and tested on a time series of measurements obtained during the SPARC2004 experiment in Barrax, Spain. Results show that the two-dimensional footprint approach yields more accurate results of aggregated sensible heat flux than traditional methods.
A qualitative description of shallow groundwater effect on surface soil temperature
Authors: Alkhaier F. , Schotting R. J. , Su Z.
Published: April 2010

Abstract. Whether or not shallow groundwater affects skin temperature is important to detect depth and extent of shallow groundwater by dint of remote sensing and important for land surface modelling studies. Although few studies have been conducted to investigate that effect, they have yielded contradicting conclusions and they stopped in 1982. To determine that shallow groundwater affects skin temperature, we measured soil temperature at two different depths (5 and 10 cm) in seven places with variable water table depths every ten minutes and for six days. After that, we correlated the minimum, maximum and average daily temperatures to average groundwater depth. We also built a simple numerical model using a differential equations solver, Flex PDE, to simulate heat transfer into soil profile and used it to simulate groundwater effect on skin temperature. We found quite high negative correlation between the maximum and average daily soil temperature and groundwater depth. Contrarily, we could hardly find any correlation between the daily minimum temperature and groundwater depth. Numerical simulations, though simple, were useful in showing that groundwater shifted skin temperature curve up in the winter and down in the summer without affecting the shape of the curve. We conclude that shallow groundwater affects skin temperature directly by its distinctive thermal properties in the soil profile and indirectly by affecting soil moisture which in turn has many different and contradictory effects on skin temperature. This study recommends building comprehensive numerical model that simulate the effect of shallow groundwater on skin temperature and on the different energy fluxes at land surface.
Distributed modeling of land surface water and energy budgets in the inland Heihe river basin of China
Authors: Jia Y. , Ding X. , Qin C. , Wang H.
Published: April 2010

Abstract. A distributed model for simulating the land surface hydrological processes in the Heihe river basin was developed and validated on the basis of considering the physical mechanism of hydrological cycle and the artificial system of water utilization in the basin. Modeling approach of every component process was introduced from 2 aspects, i.e., hydrological cycle and energy cycle. The hydrological processes include evapotranspiration, infiltration, runoff, groundwater flow, interaction between groundwater and river water, overland flow, river flow and artificial cycle processes of water utilization. A simulation of 21 years from 1982 to 2002 was carried out after obtaining various input data and model parameters. The model was validated for both the simulation of monthly discharge process and that of daily discharge process. Water budgets, spatial and temporal variations of hydrological cycle components as well as energy cycle components in the upper and middle reach Heihe basin (36 728 km2) were studied by using the distributed hydrological model. In addition, the model was further used to predict the water budgets under the future land surface change scenarios in the basin. The modeling results show: 1) in the upper reach watershed, the annual average evapotranspiration and runoff account for 63% and 37% of the annual precipitation, respectively, the snow melting runoff accounts for 19% of the total runoff and 41% of the direct runoff, and the groundwater storage has no obvious change; 2) in the middle reach basin, the annual average evapotranspiration is 52 mm more than the local annual precipitation, and the groundwater storage is of an obvious declining trend because of irrigation water consumption; 3) for the scenario of conservation forest construction in the upper reach basin, although the evapotranspiration from interception may increase, the soil evaporation may reduce at the same time, therefore the total evapotranspiration may not increase obviously; the measure of changing the farmland to animal husbandry land in the middle reach basin has obvious effects on decreasing evapotranspiration, increasing the discharge at Zhengyixia as well as decreasing the storage deficit.
Calibration of a crop model to irrigated water use using a genetic algorithm
Authors: Bulatewicz T. , Jin W. , Staggenborg S. , Lauwo S. , Miller M. , Das S. , Andresen D. , Peterson J. , Steward D. R. , Welch S. M.
Published: April 2010

Abstract. Near-term consumption of groundwater for irrigated agriculture in the High Plains Aquifer supports a dynamic bio-socio-economic system, all parts of which will be impacted by a future transition to sustainable usage that matches natural recharge rates. Plants are the foundation of this system and so generic plant models suitable for coupling to representations of other component processes (hydrologic, economic, etc.) are key elements of needed stakeholder decision support systems. This study explores utilization of the Environmental Policy Integrated Climate (EPIC) model to serve in this role. Calibration required many facilities of a fully deployed decision support system: geo-referenced databases of crop (corn, sorghum, alfalfa, and soybean), soil, weather, and water-use data (4931 well-years), interfacing heterogeneous software components, and massively parallel processing (3.8×109 model runs). Bootstrap probability distributions for ten model parameters were obtained for each crop by entropy maximization via the genetic algorithm. The relative errors in yield and water estimates based on the parameters are analyzed by crop, the level of aggregation (county- or well-level), and the degree of independence between the data set used for estimation and the data being predicted.
Linking hydropedology and ecosystem services: differential controls of surface field saturated hydraulic conductivity in a volcanic setting in central Mexico
Authors: Gómez-Tagle A.
Published: April 2010

Abstract. In this study the variation of field saturated soil hydraulic conductivity (Kfs) as key control variable and descriptor of infiltration was examined by means of a constant head single ring infiltrometer. The study took place in five coverage types and land uses in a volcanic setting in central Mexico. The tested hypothesis was that there exist a positive relationship between plant cover and surface Kfs for the study area. The examined coverage types included; Second growth pine-oak forest, pasture land, fallow land, gully and Cupresus afforestation. Results indicate that Kfs did not depend exclusively of plant cover; it was related to surface horizontal expression of the unburied soil horizons and linked to land use history. Therefore the Kfs measured at a certain location did not depend exclusively of the actual land use, it was also influenced by soil bioturbation linked to plant succession patterns and land use management practices history. The hypothesis accounts partially the variation between sites. Kfs under dense plant cover at the Cupresus afforestation was statistically equal to that measured at the fallow land or the gully sites, while second growth pine-oak forest Kfs figures were over an order of magnitude higher than the rest of the coverage types. The results suggest the relevance of unburied soil horizons in the soil hydrologic response when present at the surface. Under these conditions loosing surface soil horizons due to erosion, not only fertility is lost, but environmental services generation potential. A conceptual model within the hydropedological approach is proposed. It explains the possible controls of Kfs, for this volcanic setting. Land use history driven erosion plays a decisive role in subsurface horizon presence at the surface and soil matrix characteristic determination, while plant succession patterns seem to be strongly linked to soil bioturbation and preferential flow channel formation.
Reconstructing 20th century global hydrography: a contribution to the Global Terrestrial Network- Hydrology (GTN-H)
Authors: Wisser D. , Fekete B. M. , Vörösmarty C. J. , Schumann A. H.
Published: April 2010

Abstract. This paper presents a new reconstruction of the 20th Century global hydrography using fully coupled water balance and transport model in a flexible modeling framework. The modeling framework allows a high level of configurability both in terms of input forcings and model structure. Spatial and temporal trends in hydrological cycle components are assessed under "pre-industrial" conditions (without modern-day human activities) and contemporary conditions (incorporating the effects of irrigation and reservoir operations). The two sets of simulations allow the isolation of the trends arising from variations in the climate input driver alone and from human interventions. Our findings confirm that the expansion of irrigation and the construction has significantly and gradually impacted hydrological components in individual river basins. Variations in the volume of water entering the oceans, however, are governed by variations in the climate signal alone with human activities playing secondary role. Globally, we do find a significant trend in the terrestrial discharge over the last century. The largest impact of human intervention on the hydrological cycle arises from the operation of reservoirs that drastically changes the seasonal pattern of horizontal water transport in the river system and thereby directly and indirectly affects a number of processes.
A modeling study of heterogeneity and surface water-groundwater interactions in the Thomas Brook catchment, Annapolis Valley (Nova Scotia, Canada)
Authors: Gauthier M. J. , Camporese M. , Rivard C. , Paniconi C. , Larocque M.
Published: April 2010

Abstract. A modelling study of the impacts of subsurface heterogeneity on the hydrologic response of an 8 km2 catchment in the Annapolis Valley (Eastern Canada) is reported. The study is focused in particular on the hydraulic connection and interactions between surface water and groundwater. A coupled (1-D surface/3-D subsurface) numerical model is used to investigate, for a range of scenarios, the spatio-temporal patterns of response variables such as return flow, recharge, groundwater levels, surface saturation, and streamflow. Eight scenarios of increasing geological complexity are simulated, introducing at each step more realistic representations of the geological strata and corresponding hydraulic properties. In a ninth scenario the effects of snow accumulation and snowmelt are also considered. The results show that response variables and significant features of the catchment (e.g., springs) can be adequately reproduced using a representation of the geology and model parameter values that are based on targeted fieldwork and existing databases, and that reflect to a sufficient degree the geological and hydrological complexity of the study area. The hydraulic conductivity values of the thin surficial sediment cover (especially till) and of the North Mountain basalts emerge as key elements of the basin's heterogeneity for properly capturing the overall catchment response.
Applied tracers for the observation of subsurface stormflow at the hillslope scale
Authors: Wienhöfer J. , Germer K. , Lindenmaier F. , Färber A. , Zehe E.
Published: April 2010

Abstract. Rainfall-runoff response in temperate humid headwater catchments is mainly controlled by hydrological processes at the hillslope scale. Applied tracer experiments with fluorescent dye and salt tracers are well known tools in groundwater studies at the large scale and vadose zone studies at the plot scale, where they provide a means to characterise subsurface flow. We extend this approach to the hillslope scale to investigate saturated and unsaturated flow paths concertedly at a forested hillslope in the Austrian Alps. Dye staining experiments at the plot scale revealed that cracks and soil pipes function as preferential flow paths in the fine-textured soils of the study area, and these preferential flow structures were active in fast subsurface transport of tracers at the hillslope scale. Breakthrough curves obtained under steady flow conditions could be fitted well to a one-dimensional convection-dispersion model. Under natural rainfall a positive correlation of tracer concentrations to the transient flows was observed. The results of this study demonstrate qualitative and quantitative effects of preferential flow features on subsurface stormflow in a temperate humid headwater catchment. It turns out that, at the hillslope scale, the interactions of structures and processes are intrinsically complex, which implies that attempts to model such a hillslope satisfactorily require detailed investigations of effective structures and parameters at the scale of interest.
Comparative predictions of discharge from an artificial catchment (Chicken Creek) using sparse data
Authors: Holländer H. M. , Blume T. , Bormann H. , Buytaert W. , Chirico G. B. , Exbrayat J.-F. , Gustafsson D. , Hölzel H. , Kraft P. , Stamm C. , Stoll S. , Blöschl G. , Flühler H.
Published: April 2010

Abstract. We used ten conceptually different models to predict discharge from the artificial Chicken Creek catchment in North-East Germany. Soil textural and topography data were given to the modellers, but discharge data were withheld. We compare the predictions with the measurements from the 6 ha catchment and discuss the conceptualization and parameterization of the models. The predictions vary in a wide range, e.g. the predicted actual evapotranspiration ranged from 88 to 579 mm/y and the discharge from 19 to 346 mm/y. All model simulations revealed systematic deviations between observations of major components of the hydrological cycle (not known to the modellers) and the simulation results. Discharge was predicted mainly as subsurface discharge with little direct runoff. In reality, surface runoff was a major flow component despite the fairly coarse soil texture. The actual evapotranspiration (AET) was systematically overestimated by nine of ten models as was the ratio between actual and potential ET. Overall, none of the model simulations came close to the correct water balance during the entire 3-year study period. The comparison indicated that the personal judgement of the modellers was a major source of the differences between the model results. The most important parameters to be guessed were the soil parameters and the initial soil water content while plant parameterization had in this particular case of a sparse vegetation only a minor influence on the results.
The hydrological response of baseflow in fractured mountain areas
Authors: Millares A. , Polo M. J. , Losada M. A.
Published: April 2010

Abstract. The study of baseflow in mountainous areas of basin headwaters, where the characteristics of the often fractured materials are very different to the standard issues concerning porous material applied in conventional hydrogeology, is an essential element in the characterization and quantification of water system resources. Their analysis through recession fragments provides information on the type of response of the sub-surface and subterranean systems and on the average relation between the storage and discharge of aquifers, starting from the joining of these fragments into a single curve, the Master Recession Curve (MRC). This paper presents the generation of the downward MRC over fragments selected after a preliminary analysis of the recession curves, using a hydrological model as the methodology for the identification and the characterization of quick sub-surface flows flowing through fractured materials. The hydrological calculation has identified recession fragments through surface runoff or snowmelt and those periods of intense evapotranspiration. The proposed methodology has been applied to three sub-basins belonging to a high altitude mountain basin in the Mediterranean area, with snow present every year, and their results were compared with those for the upward concatenation of the recession fragments. The results show the existence of two different responses, one quick (at the sub-surface, through the fractured material) and the other slow, with linear behavior which takes place in periods of 10 and 17 days, respectively and which is linked to the dimensions of the sub-basin. In addition, recesses belonging to the dry season have been selected in order to compare and validate the results corresponding to the study of recession fragments. The comparison, using these two methodologies, which differ in the time period selected, has allowed us to validate the results obtained for the slow flow.
River flow forecasting with Artificial Neural Networks using satellite observed precipitation pre-processed with flow length and travel time information: case study of the Ganges river basin
Authors: Akhtar M. K. , Corzo G. A. , van Andel S. J. , Jonoski A.
Published: April 2010

Abstract. This paper explores the use of flow length and travel time as a pre-processing step for incorporating spatial precipitation information into Artificial Neural Network (ANN) models used for river flow forecasting. Spatially distributed precipitation is commonly required when modelling large basins, and it is usually incorporated in distributed physically-based hydrological modelling approaches. However, these modelling approaches are recognised to be quite complex and expensive, especially due to the data collection of multiple inputs and parameters, which vary in space and time. On the other hand, ANN models for flow forecasting are frequently developed only with precipitation and discharge as inputs, usually without taking into consideration the spatial variability of precipitation. Full inclusion of spatially distributed inputs into ANN models still leads to a complex computational process that may not give acceptable results. Therefore, here we present an analysis of the flow length and travel time as a basis for pre-processing remotely sensed (satellite) rainfall data. This pre-processed rainfall is used together with local stream flow measurements of previous days as input to ANN models. The case study for this modelling approach is the Ganges river basin. A comparative analysis of multiple ANN models with different hydrological pre-processing is presented. The ANN showed its ability to forecast discharges 3-days ahead with an acceptable accuracy. Within this forecast horizon, the influence of the pre-processed rainfall is marginal, because of dominant influence of strongly auto-correlated discharge inputs. For forecast horizons of 7 to 10 days, the influence of the pre-processed rainfall is noticeable, although the overall model performance deteriorates. The incorporation of remote sensing data of spatially distributed precipitation information as pre-processing step showed to be a promising alternative for the setting-up of ANN models for river flow forecasting.
Earth's Critical Zone and hydropedology: concepts, characteristics, and advances
Authors: Lin H. S.
Published: April 2010

Abstract. The Critical Zone (CZ) is a holistic framework for integrated studies of water with soil, rock, air, and biotic resources in terrestrial environments. This is consistent with the recognition of water as a unifying theme for research on complex environmental systems. The CZ ranges from the top of the vegetation down to the bottom of the aquifer, with a highly variable thickness (from <0.001 to >10 km). The pedosphere is the foundation of the CZ, which represents a geomembrance across which water and solutes, as well as energy, gases, solids, and organisms are actively exchanged with the atmosphere, biosphere, hydrosphere, and lithosphere to create a life-sustaining environment. Hydropedology – the science of the behaviour and distribution of soil-water interactions in contact with mineral and biological materials in the CZ – is an important contributor to CZ research. This article reviews and discusses the basic ideas and fundamental features of the CZ and hydropedology, and suggests ways for their advances. An "outward" growth model, instead of an "inward" contraction, is suggested for propelling soil science forward. The CZ is the right platform for synergistic collaborations across disciplines. The reconciliation of the geological (or "big") cycle and the biological (or "small") cycle that are orders of magnitude different in space and time is a key to understanding and predicting complex CZ processes. Because of the layered nature of the CZ and the general trend of increasing density with depth, response and feedback to climate change take longer from the above-ground zone down to the soil zone and further to the groundwater zone. Interfaces between layers and cycles are critical controls of the landscape-soil-water-ecosystem dynamics, which present fertile grounds for interdisciplinary research. Ubiquitous heterogeneity in the CZ can be addressed by environmental gradients and landscape patterns, where hierarchical structures control the landscape complex of flow networks embedded in mosaics of matrices. Fundamental issues of hydropedology are linked to the general characteristics of the CZ, including (1) soil structure and horizonation as the foundation of flow and transport characteristics in field soils; (2) soil catena and distribution pattern as a first control of water movement over the landscape; (3) soil morphology and pedogenesis as signatures of soil hydrology and soil change; and (4) soil functional classification and mapping as carriers of soil hydrologic properties and soil-landscape heterogeneity. Monitoring changes in the crucible of terrestrial life (soil) is an excellent (albeit complex) environmental assessment, as every soil is a "block of memory" of past and present biosphere-geosphere dynamics. Our capability to predict the behaviour and evolution of the CZ in response to changing environment can be improved significantly if a global alliance for monitoring, mapping, and modeling of the CZ can be fostered.
Comparison of different base flow separation methods in a lowland catchment
Authors: Gonzales A. L. , Nonner J. , Heijkers J. , Uhlenbrook S.
Published: April 2010

Abstract. Assessment of water resources kept in different storages and moving along different pathways in a catchment is important for its optimal use and protection, and also for the prediction of floods and low flows. Moreover, understanding of the runoff generation processes is essential for assessing the impacts of climate and land use changes on the hydrological response of a catchment. Many methods for base flow separation exist, but hardly one focuses on the specific behaviour of temperate lowland areas. This paper presents the results of a base flow separation study carried out in a lowland area in the Netherlands. In this research, field observations of precipitation, groundwater and surface water levels and discharges, together with tracer analysis are used to understand the runoff generation processes in the catchment. Several tracer and non-tracer based base flow separation methods were applied to the discharge time series, and their results are compared. The results show that groundwater levels react fast to precipitation events in this lowland area with shallow groundwater tables. Moreover, a good correlation was found between groundwater levels and discharges meaning that most of the measured discharge also during floods comes from the groundwater storage. It was determined using tracer hydrological approaches that approximately 90% of the total discharge is groundwater displaced by event water infiltrating in the northern part of the catchment, and only the remaining 10% is surface runoff. The impact of remote recharge causing displacement of near channel groundwater during floods could also be motivated with hydraulic approximations. The results show further that when base flow separation is meant to separate groundwater contributions to stream flow, process based methods (e.g. rating curve method; Kliner and Knezek, 1974) are more reliable than other simple non-tracer based methods. Also, the recursive filtering method (proposed by Eckhardt, 2005) can be calibrated well using the results of tracer investigation, and this resulted in good results. Consequently, simple non-tracer based base flow separation methods that could be validated for some events may provide a powerful tool for groundwater assessment or model calibration/validation in lowland areas.
Analyzing the relationship between peak runoff discharge and land-use pattern – a spatial optimization approach
Authors: Yeo I.-Y. , Guldmann J.-M.
Published: April 2010

Abstract. This paper investigates the impacts of land-use patterns on watershed hydrology and characterizes the nature of this relationship. The approach combines a spatially explicit, process-based hydrological simulation model, a land-use optimization model, the Integrated Hydrological and Land-Use Optimization (IHLUO) model, and an extensive GIS database. Numerical experiments are conducted to assess changes in the peak discharge rate under various spatial land-use arrangements, and to delineate the optimal land distribution that minimizes the peak discharge. The area of application is a catchment of the Old Woman Creek watershed in the southwestern coastal area of Lake Erie, OH. The global optimality of the delineated land pattern at a 30-m resolution is evaluated using a combinatorial statistical method. A large number of solutions has been generated from clearly different initial solutions, and these solutions turn out to be very close to each other, strongly supporting the case for a convex relationship between peak discharge and land-use pattern. The Weibull distribution is used to generate a point estimate of the global optimal value and its confidence interval. The peak discharge function is further examined in light of the underlying physics used in the simulation model.
HESS Opinions "Crash tests for a standardized evaluation of hydrological models"
Authors: Andréassian V. , Perrin C. , Berthet L. , Le Moine N. , Lerat J. , Loumagne C. , Oudin L. , Mathevet T. , Ramos M.-H. , Valéry A.
Published: April 2010

Abstract. As all hydrological models are intrinsically limited hypotheses on the behaviour of catchments, models – which attempt to represent real-world behaviours – will always remain perfectible. To progress on the long road towards improved models, we need demanding tests, i.e. true crash tests. Efficient development and assessment of hydrological models requires demanding tests on large and varied data sets to ensure models' generality, to diagnose their failures and limitations, and ultimately, to improve them.
Spatial variation in soil active-layer geochemistry across hydrologic margins in polar desert ecosystems
Authors: Barrett J. E. , Gooseff M. N. , Takacs-Vesbach C.
Published: April 2010

Abstract. Polar deserts are characterized by severe spatial-temporal limitations of liquid water. In soil active layers of the Antarctic Dry Valleys, liquid water is infrequently available over most of the arid terrestrial landscape. However, soils and sediments on the margins of glacial melt-water streams and lakes are visibly wet during the brief Austral summer when temperatures permit the existence of liquid water. We examined the role of these hydrologic margins as preferential zones for the transformation and transport of nutrient elements and solutes in an environment where geochemical weathering and biological activity is strictly limited by the dearth of liquid water. We report on hydropedological investigations of aquatic-terrestrial transition zones adjacent to 11 stream and lake systems in the Antarctic Dry Valleys. Our results show that wetted zones extended 1–11 m from the edges of lotic and lentic systems. While capillary demand and surface evaporation drive a one-way flux of water through these zones, the scale of these transition zones is determined by the topography and physical characteristics of the surrounding soils. Nutrient concentrations and fluxes appear to be influenced by both the hydrology and microbial-mediated biogeochemical processes. Salt concentrations are enriched near the distal boundary of the wetted fronts due to evapo-concentration of pore water in lake margin soils, while organic matter, ammonium and phosphate concentrations are highest in stream channel sediments where potential for biological activity is greatest. Thus, in the Antarctic Dry Valleys, intermittently wet soils on the margins of streams and lakes are important zones of both geochemical cycling and biological activity.
Analysis of the runoff generation mechanism for the investigation of the SCS-CN method applicability to a partial area experimental watershed
Authors: Soulis K. X. , Valiantzas J. D. , Dercas N. , Londra P. A.
Published: April 2010

Abstract. The Soil Conservation Service Curve Number (SCS-CN) method is widely used for predicting direct runoff volume for a given rainfall event. The applicability of the SCS-CN method and the runoff generation mechanism were thoroughly analysed in a Mediterranean experimental watershed in Greece. The region is characterized by a Mediterranean semi-arid climate. A detailed land cover and soil survey using remote sensing and GIS techniques, showed that the watershed is dominated by coarse soils with high hydraulic conductivities, whereas a smaller part is covered with medium textured soils and impervious surfaces. The analysis indicated that the SCS-CN method fails to predict runoff for the storm events studied, and that there is a strong correlation between the CN values obtained from measured runoff and the rainfall depth. The hypothesis that this correlation could be attributed to the existence of an impermeable part in a very permeable watershed was examined in depth, by developing a numerical simulation water flow model for predicting surface runoff generated from each of the three soil types of the watershed. Numerical runs were performed using the HYDRUS-1D code. The results support the validity of this hypothesis for most of the events examined where the linear runoff formula provides better results than the SCS-CN method. The runoff coefficient of this formula can be taken equal to the percentage of the impervious area. However, the linear formula should be applied with caution in case of extreme events with very high rainfall intensities. In this case, the medium textured soils may significantly contribute to the total runoff and the linear formula may significantly underestimate the runoff produced.
Catchment-scale non-linear groundwater-surface water interactions in densely drained lowland catchments
Authors: van der Velde Y. , de Rooij G. H. , Torfs P. J. J. F.
Published: April 2010

Abstract. Freely discharging lowland catchments are characterized by a strong seasonal contracting and expanding system of discharging streams and ditches. Due to this rapidly changing active channel network, discharge and solute transport cannot be modeled by a single characteristic travel path, travel time distribution, unit hydrograph, or linear reservoir. We propose a systematic spatial averaging approach to derive catchment-scale storage and discharge from point-scale water balances. The effects of spatial heterogeneity in soil properties, vegetation and drainage network are lumped and described by a relation between groundwater storage and the spatial probability distribution of groundwater depths with measurable parameters. The model describes how in lowland catchments the catchment-scale flux from groundwater to surface water via various flow routes is affected by a changing active channel network, unsaturated-saturated zone interactions and surface ponding. We used observations of groundwater levels and catchment discharge of a 6.6 km2 Dutch watershed in combination with a high-resolution spatially distributed hydrological model to test the model approach. Good results were obtained when modeling hourly discharges for a period of eight years. The validity of the underlying assumptions still needs to be tested under different conditions and for catchments of various sizes. Nevertheless, at this stage the model can already improve monitoring efficiency of groundwater-surface water interactions.
Observed drought and wetness trends in Europe: an update
Authors: Bordi I. , Fraedrich K. , Sutera A.
Published: April 2010

Abstract. Linear and nonlinear trends of drought and wetness are analysed in terms of the gridded Standardized Precipitation Index (SPI) determined from monthly precipitation in Europe (NCEP/NCAR), which characterizes the meteorological and hydrological aspects on a seasonal and on a bi-annual time scale, respectively. Two datasets are compared: one from 1949 to 1997 and the other one includes the update of the last decade (to February 2009). The following results are noted: (I) Time series of drought and wetness area coverage (number of grid points above/below the severity threshold) show a remarkable linear trend until about the end of the last century, which is reversed in the last (update) decade. This recent trend reversal is an indication of a nonlinear trend, which is more pronounced on the hydrological time scale. (II) A nonlinear trend analysis is performed based on the time series of the principal component (PC) associated to the first spatial SPI-eigenvector after embedding it in a time delay coordinate system using a sliding window of 70 months (singular spectrum analysis). Nonlinearity appears as a clear feature on the hydrological time scale. (III) The first spatial EOF-patterns of the shorter and the longer (updated) SPI time series fields show similar structure. An inspection of the SPI time behaviour at selected grid points illustrates the spatial variability of the detected trends.
Uncertainty in river discharge observations: a quantitative analysis
Authors: Di Baldassarre G. , Montanari A.
Published: April 2010

Abstract. River discharge data are known to be potentially affected by a significant uncertainty. Nevertheless, the measurement error of river flow observations is often considered negligible with respect to other uncertainties that affect hydrological studies. This paper aims at analysing and quantifying the uncertainty that may be present in river discharge records. A numerical analysis was performed on a 330-km reach of the Po River (Italy). The results show that errors in river flow data are indeed far from negligible.
Surface water acidification and critical loads: exploring the F-factor
Authors: Rapp L. , Bishop K.
Published: April 2010

Abstract. As acid deposition decreases, uncertainties in methods for calculating critical loads become more important when judgements have to be made about whether or not further emission reductions are needed. An important aspect of one type of model that has been used to calculate surface water critical loads is the empirical F-factor which estimates the degree to which acid deposition is neutralised before it reaches a lake at any particular point in time relative to the pre-industrial, steady-state water chemistry conditions. In this paper we will examine how well the empirical F-functions are able to estimate pre-industrial lake chemistry as lake chemistry changes during different phases of acidification and recovery. To accomplish this, we use the dynamic, process-oriented biogeochemical model SAFE to generate a plausible time series of annual runoff chemistry for ca 140 Swedish catchments between 1800 and 2100. These annual hydrochemistry data are then used to generate empirical F-factors that are compared to the "actual" F-factor seen in the SAFE data for each lake and year in the time series. The dynamics of the F-factor as catchments acidify, and then recover are not widely recognised. Our results suggest that the F-factor approach worked best during the acidification phase when soil processes buffer incoming acidity. However, the empirical functions for estimating F from contemporary lake chemistry are not well suited to the recovery phase when the F-factor turns negative due to recovery processes in the soil. Therefore, the empirical estimates of the F-factor are a significant source of uncertainty in the estimate of surface water critical loads and related calculations for quantifying lake acidification status, especially now that acid deposition has declined across large areas of Europe and North America.
Recent trends in groundwater levels in a highly seasonal hydrological system: the Ganges-Brahmaputra-Meghna Delta
Authors: Shamsudduha M. , Chandler R. E. , Taylor R. G. , Ahmed K. M.
Published: April 2010

Abstract. Groundwater levels in shallow aquifers underlying Asian mega-deltas are characterized by strong seasonal variations associated with monsoon rainfall. To resolve trend and seasonal components in weekly groundwater levels in the Ganges-Brahmaputra-Meghna (GBM) Delta, we apply a nonparametric seasonal-trend decomposition procedure (STL) to observations compiled from 1985 to 2005 in Bangladesh. Seasonality dominates observed variance in groundwater levels but declining groundwater levels (>1 m/yr) are detected in urban and peri-urban areas around Dhaka as well as in north-central, northwestern, and southwestern parts of the country (0.1 to 0.5 m/yr) where intensive abstraction of groundwater is conducted for dry-season rice cultivation. Rising groundwater levels (0.5 to 2.5 cm/yr) are observed in the estuarine and southern coastal regions. This novel application of the STL procedure reveals, for the first time, the unsustainability of irrigation supplied by shallow aquifers in some areas of the GBM Delta and the hydrological impact of seawater intrusion of coastal aquifers associated with sea-level rise. Our findings provide important insight into the hydrological impacts of groundwater-fed irrigation and sea-level rise in other Asian mega-deltas where monitoring data are limited.
Application of integral pumping tests to investigate the influence of a losing stream on groundwater quality
Authors: Leschik S. , Musolff A. , Krieg R. , Martienssen M. , Bayer-Raich M. , Reinstorf F. , Strauch G. , Schirmer M.
Published: April 2010

Abstract. Losing streams that are influenced by wastewater treatment plant effluents and combined sewer overflows (CSO's) can be a source of groundwater contamination. Released micropollutants such as pharmaceuticals, endocrine disrupters and other ecotoxicologically relevant substances as well as inorganic wastewater constituents can reach the groundwater, where they may deteriorate groundwater quality. This paper presents a method to quantify exfiltration mass flow rates Mex of wastewater constituents from losing streams by the operation of integral pumping tests (IPT's) up- and downstream of a target section. Due to the large sampled water volume during IPT's the results are more reliable than those from conventional point sampling. We applied the method at a test site in Leipzig (Germany). Wastewater constituents K+ and NO3− showed Mex values of 1241 to 4315 and 749 to 924 mg m−1stream d−1, respectively, while Cl− (16.8 to 47.3 g m−1stream d−1) and SO42− (20.3 to 32.2 g m−1stream d−1) revealed the highest observed Mex values at the test site. The micropollutants caffeine and technical-nonylphenol were dominated by elimination processes in the groundwater between upstream and downstream wells. Additional concentration measurements in the stream and a connected sewer at the test site were performed to identify relevant processes that influence the concentrations at the IPT wells.
Polymer tensiometers with ceramic cones: performance in drying soils and comparison with water-filled tensiometers and time domain reflectometry
Authors: van der Ploeg M. J. , Gooren H. P. A. , Bakker G. , Hoogendam C. W. , Huiskes C. , Koopal L. K. , Kruidhof H. , de Rooij G. H.
Published: April 2010

Abstract. Measuring soil water potentials is crucial to characterize vadose zone processes. Water-filled tensiometers only measure until approximately −0.085 MPa, and indirect methods may suffer from the non-uniqueness in the relationship between matric potential and measured properties. Recently developed polymer tensiometers (POTs) are able to directly measure soil matric potentials until the theoretical wilting point (−1.6 MPa). By minimizing the volume of polymer solution inside the POT while maximizing the ceramic area in contact with that polymer solution, response times drop to acceptable ranges for laboratory and field conditions. Contact with the soil is drastically improved with the use of a cone-shaped solid ceramics instead of flat ceramics. The comparison between measured potentials by polymer tensiometers and indirectly obtained potentials with time domain reflectometry highlights the risk of using the latter method at low water contents. By combining POT and time domain reflectometry readings in situ moisture retention curves can be measured over the range permitted by time domain reflectometry.