bluuebunny/crossref_metadata_2025 huggingface dataset:
Tradeoffs for the implementation of a process-based catchment model in a poorly gauged, highly glacierized Himalayan headwater
Authors: Konz M. , Uhlenbrook S. , Braun L. , Shrestha A. , Demuth S.
Published: April 2010

Abstract. The paper presents a catchment modeling approach for remote glacierized Himalayan catchments. The distributed catchment model TACD, which is widely based on the HBV model, was further developed for the application in highly glacierized catchments on a daily timestep and applied to the Nepalese Himalayan headwater Langtang Khola (360 km2). Low laying reference stations are taken for temperature extrapolation applying a second order polynomial function. Probability based statistical methods enable bridging data gaps in daily precipitation time series and the redistribution of cumulated precipitation sums over the previous days. Snow and ice melt was calculated in a distributed way based on the temperature-index method employing calculated daily potential sunshine durations. Different melting conditions of snow and ice and melting of ice under debris layers were considered. The spatial delineation of hydrological response units was achieved by taking topographic and physiographic information from maps and satellite images into account, and enabled to incorporate process knowledge into the model. Simulation results demonstrated that the model is able to simulate daily discharge for a period of 10 years and point glacier mass balances observed in the research area with an adequate reliability. The simple but robust data pre-processing and modeling approach enables the determination of the components of the water balance of a remote, data scarce catchment with a minimum of input data.
The bias in GRACE estimates of continental water storage variations
Authors: Klees R. , Zapreeva E. A. , Winsemius H. C. , Savenije H. H. G.
Published: April 2010

Abstract. The estimation of terrestrial water storage variations at river basin scale is among the best documented applications of the GRACE (Gravity and Climate Experiment) satellite gravity mission. In particular, it is expected that GRACE closes the water balance at river basin scale and allows the verification, improvement and modeling of the related hydrological processes by combining GRACE amplitude estimates with hydrological models' output and in-situ data. When computing monthly mean storage variations from GRACE gravity field models, spatial filtering is mandatory to reduce GRACE errors, but at the same time yields biased amplitude estimates. The objective of this paper is three-fold. Firstly, we want to compute and analyze amplitude and time behaviour of the bias in GRACE estimates of monthly mean water storage variations for several target areas in Southern Africa. In particular, we want to know the relation between bias and the choice of the filter correlation length, the size of the target area, and the amplitude of mass variations inside and outside the target area. Secondly, we want to know to what extent the bias can be corrected for using a priori information about mass variations. Thirdly, we want to quantify errors in the estimated bias due to uncertainties in the a priori information about mass variations that are used to compute the bias. The target areas are located in Southern Africa around the Zambezi river basin. The latest release of monthly GRACE gravity field models have been used for the period from January 2003 until March 2006. An accurate and properly calibrated regional hydrological model has been developed for this area and its surroundings and provides the necessary a priori information about mass variations inside and outside the target areas. The main conclusion of the study is that spatial smoothing significantly biases GRACE estimates of the amplitude of annual and monthly mean water storage variations. For most of the practical applications, the bias will be positive, which implies that GRACE underestimates the amplitudes. The bias is mainly determined by the filter correlation length; in the case of 1000 km smoothing, which is shown to be an appropriate choice for the target areas, the annual bias attains values up to 50% of the annual storage; the monthly bias is even larger with a maximum value of 75% of the monthly storage. A priori information about mass variations can provide reasonably accurate estimates of the bias, which significantly improves the quality of GRACE water storage amplitudes. For the target areas in Southern Africa, we show that after bias correction, GRACE annual amplitudes differ between 0 and 30 mm from the output of a regional hydrological model, which is between 0% and 25% of the storage. Annual phase shifts are small, not exceeding 0.25 months, i.e. 7.5 deg. Our analysis suggests that bias correction of GRACE water storage amplitudes is indispensable if GRACE is used to calibrate hydrological models.
Centrifuge modeling of one-step outflow tests for unsaturated parameter estimations
Authors: Nakajima H. , Stadler A. T.
Published: April 2010

Abstract. Centrifuge modeling of one-step outflow tests were carried out using a 2-m radius geotechnical centrifuge, and the cumulative outflow and transient pore pressure were measured during the tests at multiple gravity levels. Based on the scaling law of centrifuge modeling, the measurements generally showed reasonable agreement with prototype data calculated from forward simulations with input parameters determined from standard laboratory tests. The parameter optimizations were examined for three different combinations of input data sets using the test measurements. Within the gravity level examined in this study up to 40 g, the optimized unsaturated parameters compared well when accurate pore pressure measurements were included along with cumulative outflow as input data. The centrifuge modeling technique with its capability to implement variety of instrumentations under well controlled initial and boundary conditions, shortens testing time and can provide significant information for the parameter estimation procedure.
Searching for the Holy Grail of Scientific Hydrology: Qt= H(S←R←)A as closure
Authors: Beven K.
Published: April 2010

Abstract. Representative Elementary Watershed concepts provide a useful scale-independent framework for the representation of hydrological processes. The balance equations that underlie the concepts, however, require the definition of boundary flux closures. The relationship between internal state variables of an REW element and the boundary fluxes will be nonlinear, hysteretic and scale-dependent. This is demonstrated for some small experimental catchments and it is shown that at least some of this hysteresis can be represented by the use of simple transfer functions. The search for appropriate closure schemes is the second most important problem in hydrology of the 21st Century (the most important is providing the techniques to measure integrated fluxes and storages at useful scales). It is a scientific Holy Grail: worth searching for even if a general solution might ultimate prove impossible to find.
An application of the Bivariate Generalized Pareto Distribution for the probabilities of low flow extremes estimation
Authors: Jakubowski W.
Published: April 2010

Abstract. The two-dimensional Bivariate Generalized Pareto Distribution (BGPD) of Tajvidi (1996) is applied in order to estimate the extreme values of the low flow deficit amounts and durations probabilities. Eight parameters BGPD depends on two one-dimensional distributions – Univariate Generalized Pareto Distributions (UGPDs). Each of these three parameter UGPDs describes the probability of one of low flow indices. To fit BGPD into observed data a three steps method of estimation is proposed: (1) For a given shift parameter of each UGPD two others are estimated by the maximum likelihood method. (2) For given shifts and the UGPD parameters estimated in the first step the remaining ones, connected to the bivariate distribution function formula, are also estimated by the maximum likelihood method. (3) The best shift pair is chosen by maximization of the correlation coefficient of the estimated BGPD. The results are applied to statistical description of the low flow index extremes behaviour at four different catchments profiles. To extract the low flow time series data the standard constant threshold level method is applied. Finally the estimated probabilities are compared to the Zelenhasic and Salvai (1987) model.
A distributed stream temperature model using high resolution temperature observations
Authors: Westhoff M. C. , Savenije H. H. G. , Luxemburg W. M. J . , Stelling G. S. , van de Giesen N. C. , Selker J. S. , Pfister L. , Uhlenbrook S.
Published: April 2010

Abstract. Highly distributed temperature data are used as input and as calibration data for a temperature model of a first order stream in Luxembourg. A DTS (Distributed Temperature Sensing) fiber optic cable with a length of 1500 m is used to measure stream water temperature with a spatial resolution of 0.5 m and a temporal resolution of 2 min. With the observations four groundwater inflows are found and quantified (both temperature and relative discharge). They are used as input for the distributed temperature model presented here. The model calculates the total energy balance including solar radiation (with shading effects), longwave radiation, latent heat, sensible heat and river bed conduction. The simulated temperature along the whole stream is compared with the measured temperature at all points along the stream. It shows that proper knowledge of the lateral inflow is crucial to simulate the temperature distribution along the stream, and, the other way around stream temperature can be used successfully to identify runoff components. The DTS fiber optic is an excellent tool to provide this knowledge.
GIBSI: an integrated modelling system for watershed management – sample applications and current developments
Authors: Quilbé R. , Rousseau A. N.
Published: April 2010

Abstract. Hydrological and pollutant fate models have long been developed for research purposes. Today, they find an application in integrated watershed management, as decision support systems (DSS). GIBSI is such a DSS designed to assist stakeholders in watershed management. It includes a watershed database coupled to a GIS and accessible through a user-friendly interface, as well as modelling tools that simulate, on a daily time step, hydrological processes, soil erosion, agricultural pollutant transport and surface water quality. Therefore, GIBSI can be used to assess a priori the effect of management scenarios (reservoirs, land use, waste water effluents, diffuse sources of pollution that is agricultural pollution) on surface hydrology and water quality. For illustration purposes, this paper presents several management-oriented applications using GIBSI on the 6680 km2 Chaudière River watershed, located near Quebec City (Canada). They include impact assessments of: (i) timber harvesting; (ii) municipal clean water program; (iii) agricultural nutrient management scenarios; (iv) past land use evolution; (v) possible future agricultural land use evolution under climate change, as well as (vi) determination of achievable performance standards of pesticides management practices. Current and future developments of GIBSI are also presented as these will extend current uses of this tool and make it useable and applicable by stakeholders on other watersheds. Finally, the conclusion emphasizes some of the challenges that remain for a better use of DSS in integrated watershed management.
Rainfall nowcasting by at site stochastic model P.R.A.I.S.E.
Authors: Sirangelo B. , Versace P. , De Luca D. L.
Published: April 2010

Abstract. The paper introduces a stochastic model to forecast rainfall heights at site: the P.R.A.I.S.E.~model (Prediction of Rainfall Amount Inside Storm Events). PRAISE is based on the assumption that the rainfall height Hi+1 accumulated on an interval Δt between the instants iΔt and (i+1)Δt is correlated with a variable Zi(ν), representing antecedent precipitation. The mathematical background is given by a joined probability density fHi+1 Zi( ν) (hi+1 ,zi(ν)) in which the variables have a mixed nature, that is a finite probability in correspondence to the null value and infinitesimal probabilities in correspondence to the positive values. As study area, the Calabria region, in Southern Italy, was selected, to test performances of the PRAISE model.
The effectiveness of polder systems on peak discharge capping of floods along the middle reaches of the Elbe River in Germany
Authors: Huang S. , Rauberg J. , Apel H. , Lindenschmidt K.-E.
Published: April 2010

Abstract. In flood modelling, many one-dimensional (1-D) hydrodynamic models are too restricted in capturing the spatial differentiation of processes within a polder or system of polders and two-dimensional (2-D) models are very demanding in data requirements and computational resources. The latter is an important consideration when uncertainty analyses using the Monte Carlo techniques are to complement the modelling exercises. This paper describes the development of a quasi-2-D modeling approach, which still calculates the dynamic wave in 1-D but the discretisation of the computational units is in 2-D, allowing a better spatial representation of the flow in polders and avoiding large additional expenditure on data pre-processing and computational time. The model DYNHYD (1-D hydrodynamics) from the WASP5 modeling package was used as a basis for the simulations and extended to incorporate the quasi-2-D approach. A local sensitive analysis shows the sensitivity of parameters and boundary conditions on the filling volume of polders and capping of the peak discharge in the main river system. Two flood events on the Elbe River, Germany were used to calibrate and test the model. The results show a good capping effect on the flood peak by the proposed systems. The effect of capping reduces as the flood wave propagates downstream from the polders (up to 0.5 cm of capping is lost for each additional kilometer from the polders).
Rapid channel incision of the lower Pearl River (China) since the 1990s
Authors: Lu X. X. , Zhang S. R. , Xie S. P. , Ma P. K.
Published: April 2010

Abstract. This paper reported a dramatic channel incision (>10 m in the deepest cut) during the past 10 years or so in the lower Pearl River, the second largest river in terms of water discharge in China. The channel incision had caused changes both in the channel geometry as well as in the river hydraulics. Also, the water exchange between the two major tributaries of the Pearl River, the Xijiang and Beijing, had been significantly changed due to the channel incision. The rapid channel incision was principally the result of extensive sand mining in the lower Pearl River and the delta region due to the booming economy in the Pearl Delta region. Slight increase of water discharge and significant decrease of sediment load since the early 1990s in both the Xijiang and Beijiang also likely contributed to the observed dramatic river bed donwcutting to some extent. This has important implications for river management, as the large Chinese rivers have seen a dramatic depletion of sediment fluxes due to the combined effects of declining rainfall, dam constructions, water diversion, reforestation and afforestation, and sediment mining over the recent decades.
Use of soil moisture dynamics and patterns for the investigation of runoff generation processes with emphasis on preferential flow
Authors: Blume T. , Zehe E. , Bronstert A.
Published: April 2010

Abstract. Spatial patterns as well as temporal dynamics of soil moisture have a major influence on runoff generation. The investigation of these dynamics and patterns can thus yield valuable information on hydrological processes, especially in data scarce or previously ungauged catchments. The combination of spatially scarce but temporally high resolution soil moisture profiles with episodic and thus temporally scarce moisture profiles at additional locations provides information on spatial as well as temporal patterns of soil moisture at the hillslope transect scale. This approach is better suited to difficult terrain (dense forest, steep slopes) than geophysical techniques and at the same time less cost-intensive than a high resolution grid of continuously measuring sensors. Rainfall simulation experiments with dye tracers while continuously monitoring soil moisture response allows for visualization of flow processes in the unsaturated zone at these locations. Data was analyzed at different spacio-temporal scales using various graphical methods, such as space-time colour maps (for the event and plot scale) and indicator maps (for the long-term and hillslope scale). Annual dynamics of soil moisture and decimeter-scale variability were also investigated. The proposed approach proved to be successful in the investigation of flow processes in the unsaturated zone and showed the importance of preferential flow in the Malalcahuello Catchment, a data-scarce catchment in the Andes of Southern Chile. Fast response times of stream flow indicate that preferential flow observed at the plot scale might also be of importance at the hillslope or catchment scale. Flow patterns were highly variable in space but persistent in time. The most likely explanation for preferential flow in this catchment is a combination of hydrophobicity, small scale heterogeneity in rainfall due to redistribution in the canopy and strong gradients in unsaturated conductivities leading to self-reinforcing flow paths.
Response of "Glacier-Runoff" system in a typical monsoonal temperate glacier region, Hailuogou Basin in Mt. Gongga of China, to global warming
Authors:   Zongxing Li,   Yuanqing He,   Xiaomei Yang,   Xianzhong He,   Hongxi Pang,   Wenxiong Jia,   Caixia Zhang,   Linlin Yuan,   Haoyu He,   Xinxin Zuo
Published: April 2010

Abstract. The method of correlation analysis and trend analysis were used in this research in order to confirm the response of "glacier-runoff" system to global warming. Hailuogou glacier had retreated by 1871.8 m over the past 76 years, Hailuogou No. 2 glacier had also retreated by 1100 m. Glaciers retreats are contrary to the climatic warming trend in China and the Northern Hemisphere. Glaciers in Hailuogou basin were in the loss with a fluctuating manner since 1950s, and accumulative value of mass balance is −10 825.5 mm water equivalent with an annual mean value of −240.6 mm. The inverse correlation is highly significant between mass balance variation and climatic fluctuation of China and the Northern Hemisphere after 1950s. Glacier ablation is intensive with a ratio of 7.86 m yr−1. A steady rise tendency toward glaciers runoff has been observed since 1980s, and the runoff rise is mainly responsible for melt water in Hailuogou basin. It is noticeable that climatic warming not only strengthened ablation extent and enlarged ablation area, but also prolonged ablation period. Global warming is the main cause of glacier retreat, mass loss and runoff rise in Hailuogou basin.
Snow satellite images for calibration of snow dynamic in a continuous distributed hydrological model
Authors: Corbari C. , Martinelli J. , Ravazzani G. , Mancini M.
Published: April 2010

Abstract. The snow accumulation and melt processes are well known to play an important role on the river flow regime, in particular this is enhanced for basin with complex topography where the snow dynamic is strongly affected by hillslope exposition. This paper presents a simplified numerical model for snow dynamic simulation based on air temperature thresholds that rule the snow melt and accumulation processes implemented into a continuous distributed hydrological model for hydrograph simulations at basin scale. The possibility to calibrate these temperature thresholds from snow cover maps derived from NOAA satellite images is discussed. Snow covered pixels are classified according to a procedure based on aspect and elevation of each pixel, that allows to identify snow covered pixels also in shadowed areas. Snow model performance is proved at local and basin scale. The former shows a good agreement between modelled snow dynamic and observed snow height data at the Antrona station in the Toce basin; the latter shows agreement between observed and simulated hydrographs for the three gauge stations of Toce, Ticino and Maggia rivers.
SWRC fit – a nonlinear fitting program with a water retention curve for soils having unimodal and bimodal pore structure
Authors: Seki K.
Published: April 2010

Abstract. The soil hydraulic parameters for analyzing soil water movement can be determined by fitting a soil water retention curve to a certain function, i.e., a soil hydraulic model. For this purpose, the program "SWRC Fit," which performs nonlinear fitting of soil water retention curves to 5 models by Levenberg-Marquardt method, was developed. The five models are the Brooks and Corey model, the van Genuchten model, Kosugi's log-normal pore-size distribution model, Durner's bimodal pore-size distribution model, and a bimodal log-normal pore-size distribution model propose in this study. This program automatically determines all the necessary conditions for the nonlinear fitting, such as the initial estimate of the parameters, and, therefore, users can simply input the soil water retention data to obtain the necessary parameters. The program can be executed directly from a web page at http://purl.org/net/swrc/; a client version of the software written in numeric calculation language GNU Octave is included in the electronic supplement of this paper. The program was used for determining the soil hydraulic parameters of 420 soils in UNSODA database. After comparing the root mean square error of the unimodal models, the van Genuchten and Kosugi's models were better than the Brooks and Corey model. The bimodal log-normal pore-size distribution model had similar fitting performance to Durner's bimodal pore-size distribution model.
Assessment of alternative land management practices using hydrological simulation and a decision support tool: Arborea agricultural region, Sardinia
Authors: Cau P. , Paniconi C.
Published: April 2010

Abstract. Quantifying the impact of land use on water supply and quality is a primary focus of environmental management. In this work we apply a semidistributed hydrological model (SWAT) to predict the impact of different land management practices on water and agricultural chemical yield for a study site situated in the Arborea region of central Sardinia, Italy. The physical processes associated with water movement, crop growth, and nutrient cycling are directly modeled by SWAT. The model simulations are used to identify indicators that reflect critical processes related to the integrity and sustainability of the ecosystem. Specifically we focus on stream quality and quantity indicators associated with anthropogenic and natural sources of pollution. A multicriteria decision support system is then used to develop the analysis matrix where water quality and quantity indicators for the rivers, lagoons, and soil are combined with socio-economic variables. The DSS is used to assess four options involving alternative watersheds designated for intensive agriculture and dairy farming and the use or not of treated wastewater for irrigation.
Parameter extrapolation to ungauged basins with a hydrological distributed model in a regional framework
Authors: Vélez J. J. , López Unzu F. , Puricelli M. , Francés F.
Published: April 2010

Abstract. A Regional Water Resources study was performed at basins within and draining to the Basque Country Region (N of Spain), with a total area of approximately 8500 km2. The objective was to obtain daily and monthly long-term discharges in 567 points, most of them ungauged, with basin areas ranging from 0.25 to 1850 km2. In order to extrapolate the calibrations at gauged points to the ungauged ones, a distributed and conceptually based model called TETIS was used. In TETIS the runoff production is modelled using five linked tanks at each cell with different outflow relationships at each tank, which represents the main hydrological processes as snowmelt, evapotranspiration, surface runoff, interflow and base flow. The routing along the channels' network couples its geomorphologic characteristics with the kinematic wave approach. The parameter estimation methodology tries to distinguish between the effective parameter used in the model at cell scale, and the watershed characteristic estimated from the available information, being the best estimation without losing its physical meaning. The relationship between them can be considered as a correction function or, in its simple form, a correction factor. The correction factor can take into account the model input errors, the temporal and spatial scale effects and the watershed characteristics. Therefore, it is reasonable to assume the correction factor is the same for each parameter to all cells within the watershed. This approach reduces dramatically the number of parameter to be calibrated, because only the common correction factors are calibrated instead of parameter maps (number of parameters times the number of cells). In this way, the calibration can be performed using automatic methodologies. In this work, the Shuffled Complex Evolution – University of Arizona, SCE-UA algorithm was used. The available recent year's data was used to calibrate the model in 20 of the most representative flow gauge stations in 18 basins with a Nash-Sutcliffe index higher than 0.6 (10 higher than 0.8). The calibrated correction factors at each basin were similar but not equal. The validation process (in time and space) was performed using the remaining data in all flow gauge stations (62), with 42 basins with a Nash-Sutcliffe index higher than 0.5 (25 higher than 0.7). Deficient calibration and validations were always related with flow gauge stations very close to the karstic springs. These results confirmed that it was feasible and efficient to use the SCE-UA algorithm for the automatic calibration of distributed conceptual models and the calibrated model could be used at ungauged basins. Finally, meteorological information from the past 50 years at a daily scale was used to generate a daily discharges series at 567 selected points.
A coupled atmosphere and multi-layer land surface model for improving heavy rainfall simulation
Authors: Haggag M. , Yamashita T. , Lee H. , Kim K.
Published: April 2010

Abstract. A multi-layer land surface model (SOLVEG) is dynamically coupled to the non-hydrostatic atmospheric model (MM5) in order to represent better spatial variations and changes in land surface characteristics compared with the land surface parameterization schemes included in the MM5. In this coupling, calculations of the atmosphere and land surface models are carried out as independent tasks of different processors; a model coupler controls these calculations and data exchanges among models using Message Passing Interface (MPI). This coupled model is applied to the record-breaking heavy rain events occurred in Kyushu Island, the southernmost of Japan's main islands, from 20 July to 25 July in 2006. The test computations are conducted by using both the developed coupled model and the original land surface parameterization of MM5. The result of these computations shows that SOLVEG reproduce higher ground temperature than land surface parameterization schemes in the MM5. This result indicates the feedback of land surface processes between MM5 and SOLVEG plays an important role in the computation. The most pronounced difference is in the rainfall simulation that shows the importance of coupling SOLVEG and MM5. The coupled model accurately reproduces the heavy rainfall events observed in Kyushu Island compared to the original MM5 from both the spatial and temporal point of view. This paper clearly shows that realistic simulation of rainfall event strongly depends on land-surface processes interacting with cloud development that depends on surface heat and moisture fluxes, which in turn are mainly determined by land surface vegetation and soil moisture storage. Soil temperature/moisture changes significantly affect the localized precipitation and modest improvement in the land surface representation can enhance the heavy rain simulation. MM5-SOLVEG coupling shows a clear image of land surface-atmosphere interactions and the dynamic feedback on convection initiation, storm propagation and precipitation.
Storage and transport in cave seepage- and groundwater in a South German karst system
Authors: Schwarz K. , Barth J. A. C. , Grathwohl P. , Postigo-Rebello C.
Published: April 2010

Abstract. We investigated one of the best-known and second largest karst areas in Germany (Blautopf Catchment) that offers a unique access waters of the unsaturated zone through a large cave system. As tracers for water flow and storage we measured stable isotopes (18O/16O and D/H ratios) in precipitation, seepage- and groundwater. The precipitation showed a distinct seasonal cycle with δ18O values between −2.6 and −22.6‰ during summer and winter, respectively. However, the isotope signals in seepage water in the caves as well as the discharge were completely buffered and ranged around an average δ18O value of −10‰. This value also matched the long-term average of the precipitation. In addition, the homogeneous isotopic composition of the Blautopf Spring was against expectation for its highly variable discharge (0.3 to 32 m3 s−1) that is typical for a fast responsive karst system. We explain the isotopic similarity between cave seepage and the Blautopf Spring (as an integral signal for groundwater) by nearly complete mixing of the water already in the vadose zone. The latter can be divided into the compartments soil, epikarst and rock matrix that all have good storage capacities and also allow diffusive exchange of solutes between mobile and less mobile matrix water. The above approach revealed new aspects about turnover and flow paths of the infiltrated water and thus helps to constrain the risk by pollution to the groundwater.
Impacts of climate change on Blue Nile flows using bias-corrected GCM scenarios
Authors: Elshamy M. E. , Seierstad I. A. , Sorteberg A.
Published: April 2010

Abstract. Global circulation models (GCMs) depict different pictures for the future of Nile basin flows in general and for the Blue Nile sub-basin in particular. This study analyses the output of 17 GCMs included in the 4th IPCC assessment report. Downscaled precipitation and potential evapotranspiration (PET) scenarios for the 2081–2098 period were constructed for the upper Blue Nile basin. These were used to drive a fine-scale hydrological model of the Nile Basin to assess their impacts on the flows of the upper Blue Nile at Diem, which accounts for about 60% of the total annual Nile yield. All models showed increases in temperature with annual values ranging from 2°C to 5°C. All GCMs also showed increases in total annual PET varying from +2 to +14%. GCMs disagreed on precipitation changes with values between −15% and +14%, but more models reported reductions (10) than those reporting increases (7). The ensemble mean of the 17 GCMs showed no change. Compounded with the high climatic sensitivity of the basin, the annual flow changed by values ranging between −60% to +45%. The increase in PET either offsets the increase in rainfall or exacerbates its reduction and the ensemble mean flow is reduced by 15%. The results were also used to study the linkages between temperature, rainfall, PET and flow. Simple relationships are devised that can be used to estimate the impacts of climate change and facilitate comparison with output from other hydrological models and GCMs.
Lateral inflow into the hyporheic zone tested by a laboratory model
Authors: Chou P. Y. , Wyseure G.
Published: April 2010

Abstract. Groundwater and river water with a different composition interact and exchange in the hyporheic zone. The study of hyporheic zone and its impact on water quality has recently received growing interest because of its role in nutrients and pollutants interactions between rivers and the aquifer. In this research our main purpose is to identify the physical processes and characteristics needed for a numerical model, which include the unsaturated recharge zone, the aquifer and the river bed. In order to investigate such lateral groundwater inflow process, a laboratory J-shaped column experiment was designed. This study determined the transport parameters of the J-shaped column by fitting an analytical solution of the convective-dispersion equation on individual segments to the observed resident breakthrough curves, and by inverse modelling on the entire flow domain for every flux. The obtained transport parameters relation was tested by numerical simulation using HYDRUS 2D/3D. Four steady-state flux conditions (i.e. 0.5 cm hr−1, 1 cm hr−1, 1.5 cm hr−1 and 2 cm hr−1) were applied, transport parameters including pore water velocity and dispersivity were determined for both unsaturated and saturated sections along the column. Results showed that under saturated conditions the dispersivity was fairly constant and independent of the flux. In contrast, dispersivity under unsaturated conditions was flux dependent and increased at lower flux. For our porous medium the dispersion coefficient related best to the quotient of the pore water velocity divided by the water content. A simulation model of the hyporheic exchange of the water and dissolved materials should take this into account.
Modelling dominant runoff production processes at the micro-scale – a GIS-based and a statistical approach
Authors: Müller C. , Hellebrand H. , Seeger M. , Schobel S.
Published: April 2010

Abstract. In this study two approaches are presented to model Dominant Runoff production Processes (DRP) with respect to regionalization. The approaches have been developed in the micro-scale experimental Zemmer basin (Germany). The first approach combines the permeability of the substratum, land-use and slope of the basin in a GIS-based analysis. The second approach makes use of discriminant analysis of the physiographic characteristics of the basin and links it to the GIS analysis. The net results were two maps indicating modelled DRP for the Zemmer basin, which were then compared to an existing DRP map of the Zemmer basin. Both approaches provided satisfactory results when compared to this existing DRP map. The first approach was strongly linked to the geological conditions of the basin while the second approach revealed a strong dependence on the topography. Therefore, impermeability of the substratum and the topography of the basin were used as suitable parameters for modelling dominant runoff processes.
Road and stream network connectivity and potential: northeastern Puerto Rico, an exploratory analysis
Authors: Sherrill K. R. , Laituri M. J. , Helmer E. H. , Ramirez J. A. , Blanco J. F. , Hein K. , Pike A. S.
Published: April 2010

Abstract. Interactions between road and stream networks are complex and are influenced by a range of environmental and road design characteristics. These interactions are not clearly understood and are the subjects of current research. To increase understanding of these interactions we explore the concepts of Road and Stream Network Connectivity (R/S Connectivity) and Road and Stream Network Connectivity Potential (RSNCP). Lastly we provide a methodology for study and analysis of R/S connectivity. This study focuses on road induced alterations to sediment and water flow processes, which are important road effects of R/S connectivity. For 25 river road crossings (RRC) in the Rio Mameyes and Rio Espiritu watersheds of Northeastern Puerto Rico, a multi-scale Geographic Information Systems (GIS) database measuring environmental and road characteristic variables was developed specifically to measure variables influencing sediment and water flow. Multivariate analysis methods were used to select the environmental and road characteristic variables which were used in multiple linear regression models for three biota variables (Decapod Richness, Adult Fish Richness, and Total Richness), and four stream habitat geomorphology variables (Median Channel Grain Size, Active Channel Maximum Depth, Pool Volume, and Active Channel Width). Explained variance (R2) from modeling results ranged from 0.22 to 0.86, demonstrating that the GIS derived variables can successfully be used to model important stream biota and geomorphology response variables.
Does evaporation paradox exist in China?
Authors: Cong Z. T. , Yang D. W.
Published: April 2010

Abstract. One expected consequence of global warming is the increase in evaporation. However, lots of observations show that the rate of evaporation from open pans of water has been steadily decreasing all over the world in the past 50 years. The contrast between expectation and observation is called the evaporation paradox. Based on data from 317 weather stations in China from 1956 to 2005, the trends of pan evaporation and air temperature were obtained and evaporation paradox was analyzed. The following conclusions were made: (1) From 1956 to 2005, pan evaporation paradox exists in China as a whole with decreasing in pan evaporation and the warming though it does not exist in Northeast and Southeast; (2) From 1956 to 1985, pan evaporation paradox exists narrowly as a whole with unobvious warming though it does not exist in Northeast (3) From 1986 to 2005, in the past 50 years, the precipitation and the pan evaporation exhibit contrary trend in most areas. Furthermore, pan evaporation paradox does not exist as a whole with increasing in pan evaporation though it exists in South. Furthermore, the trend of other weather factors including sunlight time, windspeed, humidity and vapor pressure deficit and their relation with pan evaporation are discussed. It can be concluded that pan evaporation decreasing is caused by the decreasing in radiation and wind speed before 1985 and pan evaporation increasing is caused by the deceasing in vapor pressure deficit due to strong warming after 1986.
Vegetation dynamics and soil water balance in a water-limited Mediterranean ecosystem on Sardinia, Italy
Authors: Montaldo N. , Albertson J. D. , Mancini M.
Published: April 2010

Abstract. Mediterranean ecosystems are commonly heterogeneous savanna-like ecosystems, with contrasting plant functional types (PFTs, e.g., grass and woody vegetation) competing for the water use. Mediterranean ecosystems are also commonly characterized by strong inter-annual rainfall variability, which influences the distributions of PFTs that vary spatially and temporally. With the objective to investigate interactions between vegetation dynamics, soil water budget and land-surface fluxes in a water-limited ecosystem, an extensive field campaign in a Mediterranean setting was performed. Also a vegetation dynamic model (VDM) is coupled to a 3-component (bare soil, grass and woody vegetation) Land surface model (LSM). The case study is in Orroli, situated in the mid-west of Sardegna within the Flumendosa river basin. The landscape is a mixture of Mediterranean patchy vegetation types: trees, including wild olives and cork oaks, different shrubs and herbaceous species. Land surface fluxes, soil moisture and vegetation growth were monitored during the May 2003–June 2006 period. Interestingly, hydrometeorological conditions of the monitored years strongly differ, with dry and wet years in turn, such that a wide range of hydrometeorological conditions can be analyzed. The coupled VDM-LSM model is successfully tested for the case study, demonstrating high model performance for the wide range of eco-hydrologic conditions. The use of the VDM in the LSM is demonstrated to be essential when studying the climate-soil-vegetation interactions of these water-limited ecosystems. Results demonstrate also that vegetation dynamics are strongly influenced by the inter-annual variability of atmospheric forcing, with grass leaf area index changing significantly each spring season according to seasonal rainfall amount.
An evaluation of ASCAT surface soil moisture products with in-situ observations in southwestern France
Authors: Albergel C. , Rüdiger C. , Carrer D. , Calvet J.-C. , Fritz N. , Naeimi V. , Bartalis Z. , Hasenauer S.
Published: April 2010

Abstract. A long term data acquisition effort of profile soil moisture is currently underway at 13 automatic weather stations located in southwestern France. In this study, the soil moisture measured in-situ at 5 cm is used to evaluate the normalised surface soil moisture (SSM) estimates derived from coarse-resolution (25 km) active microwave data of the ASCAT scatterometer instrument (onboard METOP), issued by EUMETSAT for a period of 6 months (April–September) in 2007. The seasonal trend is removed from the satellite and in-situ time series by considering scaled anomalies. One station (Mouthoumet) of the ground network, located in a mountainous area, is removed from the analysis as very few ASCAT SSM estimates are available. No correlation is found for the station of Narbonne, which is close to the Mediterranean sea. On the other hand, the other 11 stations present significant correlation levels. The soil moisture measured in-situ at those stations, at 30 cm, is used to estimate the characteristic time length (T) of an exponential filter applied to the ASCAT product. The best correlation between a soil water index derived from ASCAT and the in-situ soil moisture observations at 30 cm is obtained with a T-value of 14 days.
Quantifying the effect of land use and land cover change on green water and blue water in northern part of China
Authors: Liu X. , Ren L. , Yuan F. , Singh V. P. , Fang X. , Yu Z. , Zhang W.
Published: April 2010

Abstract. In order to investigate the effect of land use and land cover changes on hydrological process in northern parts of China, a distributed hydrological model was developed and applied in the Laohahe catchment. The direct evaporation from the intercepted water, potential canopy transpiration and potential soil evaporation were computed using a physically-based two-source potential evapotranspiration model, which would be regarded as input to the distributed hydrological model for the computation of actual evaportranspiration. Runoff generation was based on mixed runoff mechanisms of infiltration excess runoff and saturation excess runoff and the Muskingum-Cunge method was adopted for flow routing. The land cover data were available for 1980, 1989, 1996 and 1999. Daily streamflow measurements were available from 1964 to 2005 and were divided into 4 periods: 1964–1979, 1980–1989, 1990–1999 and 2000–2005, based on the land cover scenarios. The distributed hydrological model was coupled with a two-source potential evaportranspiration model for simulating daily runoff. The result of runoff simulation showed that the saturation excess runoff generation was dominant in the catchment. Model parameters were calibrated using hydrometeorological and land cover data corresponding to the same period. Streamflow simulation was conducted for each period under these four land cover scenarios. The results showed that the change of land use and land cover had a significant influence on evapotranspiration and runoff. The land cover data showed that forest land and water body had decreased from 1980 through 1999 and farm land and grass land had increased. This change caused the vegetation interception evaporation and vegetation transpiration to decrease, whereas the soil evaporation tended to increase. Thus the green water decreased but the blue water increased over the Laohahe catchment. This result was inconsistent with the fact that runoff ratio had a tendency of decrease in the catchment in 2000. It is this reason that water use out of stream channel has been increasing in recent years.
Impacts of changes in vegetation cover on soil water heat coupling in an alpine meadow, Qinghai-Tibet Plateau, China
Authors: Genxu W. , Hongchang H. , Yuanshou L. , Yibo W.
Published: April 2010

Abstract. Alpine meadow is one of the most widespread grassland types in the permafrost regions of the Qinghai-Tibet Plateau. The transmission of coupled soil water heat is one of the most important processes influencing cyclic variations in the hydrology of frozen soil regions, especially under conditions of changing vegetation cover. The present study assesses the impact of changes in vegetation cover on the coupling of soil water and heat in a permafrost region. Soil moisture (θv), soil temperature (Ts), soil heat content, and differences in θv−Ts coupling were monitored on a seasonal and daily basis under three different densities of vegetation cover (30, 65, and 93%) upon both thawed and frozen soils. Regression analysis of θv vs. Ts plots under different levels of vegetation cover indicates that soil freeze-thaw processes were significantly affected by changes in vegetation cover. With decreasing vegetation cover upon an alpine meadow, the difference between air temperature and ground temperature (ΔTa−s) also decreased. A decrease in vegetation cover also resulted in a decrease in the Ts at which soil froze and an increase in the temperature at which it thawed; this was reflected in a greater response of soil temperature to changes in air temperature (Ta). For ΔTa−s outside the range of −0.1 to 1.0°C, root zone soil-water temperatures showed a significant increase with increasing ΔTa−s; however, the magnitude of this relationship was dampened with increasing vegetation cover. At the time of maximum water content in the thawing season, the soil temperature decreased with increasing vegetation. Changes in vegetation cover also led to variations in θv−Ts coupling. With increasing vegetation cover, the surface heat flux increased, along with the amplitude of its variations. Soil heat storage at 20 cm depth also increased with increasing vegetation cover, and the downward transmitted of heat flux decreased. In addition to providing insulation against soil warming, vegetation in alpine meadows within the permafrost region also slows down the response of permafrost to climatic warming via the greater water-holding capacity of its root zone. Such vegetation may therefore play an important role in conserving water in alpine meadows and maintaining the stability of engineering works constructed within frozen soil of the Qinghai-Tibet Plateau.
Large-scale lysimeter site St. Arnold, Germany: analysis of 40 years of precipitation, leachate and evapotranspiration
Authors: Harsch N. , Brandenburg M. , Klemm O.
Published: April 2010

Abstract. This study deals with a lysimetrical-meteorological data series collected on the large-scale lysimeter site "St. Arnold", Germany, from November 1965 to April 2007. The particular relevance of this data rests both upon its perdurability and upon the fact that the site is comprised of a grassland basin, an oak/beech and a pine basin1. Apart from analyzing secular trends of the meteorological measurements, the primary objective of this study is the evaluation of precipitation in connection with leachate quantities and potential and actual evapotranspiration. The latter are based upon the Penman and the Penman-Monteith approaches, respectively. The main results of this survey are that, on a long-term average, the grassland basin turns more than half (53%) of its annually incoming precipitation into leachate and only 36% into water vapour, while the deciduous forest exhibits a rather balanced ratio with 37% for leachate and 44% for evapotranspiration, and the evergreen coniferous forest shows the highest evaporation rate (56%) and the lowest leachate rate (28%). Concerning these water balances, considerable differences both between basins and between seasons stand out. While summer periods exhibit high evapotranspiration rates for the forests and moderate ones for the grassland, winter periods are characterised by considerable leachate quantities for grassland and the deciduous forest and moderate ones for the coniferous forest. Following the analysis of the climatic development in St. Arnold, trends towards a milder and more humid regional climate were detected. 1According to a survey conducted by Lanthaler in 2006, only 1% of all European lysimeters are planted with forests. Leading varieties are fields (63%) and grassland (21%).