bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of two model approaches in the Zambezi river basin with regard to model reliability and identifiability
Authors: Winsemius H. C. , Savenije H. H. G. , Gerrits A. M. J. , Zapreeva E. A. , Klees R.
Published: April 2010

Abstract. Variations of water stocks in the upper Zambezi river basin have been determined by 2 different hydrological modelling approaches. The purpose was to provide preliminary terrestrial storage estimates in the upper Zambezi for comparison with estimates derived from the Gravity Recovery And Climate Experiment (GRACE). The first modelling approach is GIS-based, distributed and conceptual (STREAM). The second approach uses lumped elementary watersheds identified and modelled conceptually (LEW). The STREAM model structure has been assessed using GLUE (Generalized Likelihood Uncertainty Estimation) a posteriori to determine parameter identifiability. The LEW approach could, in addition, be tested for model structure, because computational efforts of LEW are low. Both models are threshold models, where the non-linear behaviour of the Zambezi river basin is explained by a combination of thresholds and linear reservoirs. The models were forced by time series of gauged and interpolated rainfall. Where available, runoff station data was used to calibrate the models. Ungauged watersheds were generally given the same parameter sets as their neighbouring calibrated watersheds. It appeared that the LEW model structure could be improved by applying GLUE iteratively. Eventually, it led to better identifiability of parameters and consequently a better model structure than the STREAM model. Hence, the final model structure obtained, better represents the true hydrology. After calibration, both models show a comparable efficiency in representing discharge. However the LEW model shows a far greater storage amplitude than the STREAM model. This emphasizes the storage uncertainty related to hydrological modelling in data-scarce environments such as the Zambezi river basin. It underlines the need and potential for independent observations of terrestrial storage to enhance our understanding and modelling capacity of the hydrological processes. GRACE could provide orthogonal information that can help to constrain and further enhance our models. In the near future, other remotely sensed data sources will be used to force modelling efforts of the Zambezi (e.g. satellite rainfall estimates) and to identify individual storage components in the GRACE observations (e.g. altimeter lake levels and microwave soil moisture). Ultimately, this will create possibilities for state updating of regional hydrological models using GRACE.
Hydroclimatology of the Nile: results from a regional climate model
Authors: Mohamed Y. A. , van den Hurk B. J. J. M. , Savenije H. H. G. , Bastiaanssen W. G. M.
Published: April 2010

Abstract. This paper is the result of the first regional coupled climatic and hydrologic model of the Nile. For the first time the interaction between the climatic processes and the hydrological processes on the land surface have been fully coupled. The hydrological model is driven by the rainfall and the energy available for evaporation generated in the climate model, and the runoff generated in the catchment is again routed over the wetlands of the Nile to supply moisture for atmospheric feedback. The results obtained are surprisingly accurate given the extremely low runoff coefficients in the catchment. The paper presents model results over the sub-basins: Blue Nile, White Nile, Atbara river and the Main Nile for the period 1995 to 2000, but focuses on the Sudd swamp. Limitations in both the observational data and the model are discussed. It is concluded that the model provides a sound representation of the regional water cycle over the Nile. The model is used to describe the regional water cycle in the Nile basin in terms of atmospheric fluxes, land surface fluxes and land surface-climate feedbacks. The monthly moisture recycling ratio (i.e. locally generated/total precipitation) over the Nile varies between 8 and 14%, with an annual mean of 11%, which implies that 89% of the Nile water resources originates from outside the basin physical boundaries. The monthly precipitation efficiency varies between 12 and 53%, and the annual mean is 28%. The mean annual result of the Nile regional water cycle is compared to that of the Amazon and the Mississippi basins.
Impact of phosphorus control measures on in-river phosphorus retention associated with point source pollution
Authors: Demars B. O. L. , Harper D. M. , Pitt J.-A. , Slaughter R.
Published: April 2010

Abstract. In-river phosphorus retention alters the quantity and timings of phosphorus delivery to downstream aquatic systems. Many intensive studies of in-river phosphorus retention have been carried out but generally on a short time scale (2-4 years). In this paper, monthly water quality data, collected by the Environment Agency of England and Wales over 12 years (1990-2001), were used to model daily phosphorus fluxes and monthly in-river phosphorus retention in the lowland calcareous River Wensum, Norfolk, UK. The effectiveness of phosphorus stripping at two major sewage treatment works was quantified over different hydrological conditions. The model explained 78% and 88% of the observed variance before and after phosphorus control, respectively. During relatively dry years, there was no net export of phosphorus from the catchment. High retention of phosphorus occurred, particularly during the summer months, which was not compensated for, by subsequent higher flow events. The critical discharge (Q) above which net remobilisation would occur, was only reached during few, high flow events Q25-Q13. Phosphorus removal from the effluent at two major STWs (Sewage Treatment Works) reduced the phosphorus catchment mass balance variability by 20-24% under the Q99-Q1. range of flow conditions. Although the absorbing capacity of the catchment against human impact was remarkable, further phosphorus remedial strategies will be necessary to prevent downstream risks of eutrophication occuring independently of the unpredictable variability in weather conditions.
A comparison of regionalisation methods for catchment model parameters
Authors: Parajka J. , Merz R. , Blöschl G.
Published: April 2010

Abstract. In this study we examine the relative performance of a range of methods for transposing catchment model parameters to ungauged catchments. We calibrate 11 parameters of a semi-distributed conceptual rainfall-runoff model to daily runoff and snow cover data of 320 Austrian catchments in the period 1987-1997 and verify the model for the period 1976-1986. We evaluate the predictive accuracy of the regionalisation methods by jack-knife cross-validation against daily runoff and snow cover data. The results indicate that two methods perform best. The first is a kriging approach where the model parameters are regionalised independently from each other based on their spatial correlation. The second is a similarity approach where the complete set of model parameters is transposed from a donor catchment that is most similar in terms of its physiographic attributes (mean catchment elevation, stream network density, lake index, areal proportion of porous aquifers, land use, soils and geology). For the calibration period, the median Nash-Sutcliffe model efficiency ME of daily runoff is 0.67 for both methods as compared to ME=0.72 for the at-site simulations. For the verification period, the corresponding efficiencies are 0.62 and 0.66. All regionalisation methods perform similar in terms of simulating snow cover.
Variability in stream discharge and temperatures during ecologically sensitive time periods: a preliminary assessment of the implications for Atlantic salmon
Authors: Tetzlaff D. , Soulsby C. , Youngson A. F. , Gibbins C. , Bacon P. J. , Malcolm I. A. , Langan S.
Published: April 2010

Abstract. This study focused on improving the understanding of the temporal variability in hydrological and thermal conditions and their potential influences on two life stages of Atlantic salmon (Salmo salar) – stream resident juveniles and returning adult spawners. Stream discharges and temperatures in the Girnock Burn, NE Scotland, a small nursery stream, were characterised over a time period of ten hydrological years (1994/95–2003/04). Frequency, magnitude, duration and timing of thermal, hydraulic and hydrological conditions were examined using data with a high temporal resolution (hourly and subhourly). Particular attention was focussed on assessing variations during ecologically sensitive time periods when salmon behaviour is most susceptible to environmental perturbations. The Girnock Burn was characterised by a strong inter- and intra-annual variability in the hydrological and thermal regime. This has clear implications for the likely feeding opportunities for juvenile fish in winter and early spring and the emergence of fry in the late spring. The movement of adult spawners towards breeding areas showed a complex dependence on hydrological variability. If discharges were low, fish movement was increasingly triggered by suboptimal flow increases as spawning time approached. Elucidating links between discharge/temperature variability and salmon habitat availability and utilization at appropriately fine temporal scales is a prerequisite to the development of better conservation management strategies and more biologically meaningful flow regimes in regulated river systems.
Comparative analysis of the actual evapotranspiration of Flemish forest and cropland, using the soil water balance model WAVE
Authors: Verstraeten W. W. , Muys B. , Feyen J. , Veroustraete F. , Minnaert M. , Meiresonne L. , De Schrijver A.
Published: April 2010

Abstract. This paper focuses on the quantification of the green – vegetation related – water flux of a forest stand in the temperate lowland of Flanders. The underlying reason of the research was to develop a methodology for assessing the impact of forests on the hydrologic cycle in comparison to agriculture. The approach tested for calculating the water consumption by forests was based on the application of the soil water balance model WAVE. The study involved the collection of data from 14 forest stands, the calibration and validation of the WAVE model, and the comparison of the water use (WU) components - transpiration, soil and interception evaporation - between forest and cropland. For model calibration purposes simulated and measured time series of soil water content at different soil depths, period March 2000–August 2001, were compared. A multiple-site validation was conducted as well. Actual tree transpiration calculated with sap flow measurements in three forest stands gave similar results for two of the three stands of pine (Pinus sylvestris L.), but WAVE overestimated the actual measured transpiration for a stand of poplar (Populus sp.). A useful approach to compare the WU components of forest versus cropland is scenario analysis based on the validated WAVE model. The statistical Profile Analysis method was implemented to explore and analyse the simulated WU time-series. With an average annual rainfall of 819 mm, the results show that forests in Flanders consume more water than agricultural crops. A 30 years average of 491 mm for 10 forests stands versus 398 mm for 10 cropped agricultural fields was derived. The WU components, on yearly basis, also differ between the two land use types (transpiration: 315 mm for forest and 261 mm for agricultural land use; soil evaporation: 47 mm and 131 mm, for forest and cropland, respectively). Forest canopy interception evaporation was estimated at 126 mm, while it was negligible for cropland.
Resolving conflicting objectives in the management of the Plastiras Lake: can we quantify beauty?
Authors: Christofides A. , Efstratiades A. , Sargentis G.-F. , Koutsoyiannis D. , Hadjibiros K.
Published: April 2010

Abstract. The possible water management of the Plastiras Lake, an artificial reservoir in central Greece, is examined. The lake and surrounding landscape is aesthetically degraded when the water level drops, and the requirement of maintaining a high quality of the scenery constitutes one of the several conflicting water uses, the other ones being irrigation, water supply, and power production. This environmental water use, and, to a lesser extent, the requirement for adequate water quality, results in constraining the annual release. Thus, the allowed fluctuation of reservoir stage is not defined by the physical and technical characteristics of the reservoir, but by a multi-criteria decision, the three criteria being maximizing water release, ensuring adequate water quality, and maintaining a high quality of the natural landscape. Each of these criteria is analyzed separately. The results are then put together in a multicriterion tableau, which helps understand the implications of the possible alternative decisions. Several conflict resolution methods are overviewed, namely willingness to pay, hedonic prices, and multi-criteria decision analysis. All these methods attempt to quantify non-quantifiable qualities, and it is concluded that they don't necessarily offer any advantage over merely making a choice based on understanding.
A daily water balance model for representing streamflow generation process following land use change
Authors: Bari M. A. , Smettem K. R. J.
Published: April 2010

Abstract. A simple conceptual water balance model representing the streamflow generation processes on a daily time step following land use change is presented. The model consists of five stores: (i) Dry, Wet and Subsurface Stores for vertical and lateral water flow, (ii) a transient Stream zone Store (iii) a saturated Goundwater Store. The soil moisture balance in the top soil Dry and Wet Stores are the most important component of the model and characterize the dynamically varying saturated areas responsible for surface runoff, interflow and deep percolation. The Subsurface Store describes the unsaturated soil moisture balance, extraction of percolated water by vegetation and groundwater recharge. The Groundwater Store controls the baseflow to stream (if any) and the groundwater contribution to the stream zone saturated areas. The daily model was developed following a "downward approach" from an earlier monthly model and performed very well in simulating daily flow generation processes observed at Ernies (control) and Lemon (53% cleared) catchments in Western Australia. Most of the model parameters were incorporated a priori from catchment attributes such as surface slope, soil depth, porosity, stream length and initial groundwater depth, and some were calibrated by matching the observed and predicted hydrographs. The predicted groundwater depth, and streamflow volumes across all time steps from daily to monthly to annual were in close agreement with observations for both catchments.
Optimal estimator for assessing landslide model efficiency
Authors: Huang J. C. , Kao S. J.
Published: April 2010

Abstract. The often-used success rate (SR) in measuring cell-based landslide model efficiency is based on the ratio of successfully predicted unstable cells over total actual landslide sites without considering the performance in predicting stable cells. We proposed a modified SR (MSR), in which we include the performance of stable cell prediction. The goal and virtue of MSR is to avoid over-prediction while upholding stable sensitivity throughout all simulated cases. Landslide susceptibility maps (a total of 3969 cases) with full range of performance (from worse to perfect) in stable and unstable cell predictions are created and used to probe how estimators respond to model results in calculating efficiency. The kappa method used for satellite image analysis is drawn for comparison. Results indicate that kappa is too stern for landslide modeling giving very low efficiency values in 90% simulated cases. The old SR tends to give high model efficiency under certain conditions yet with significant over-prediction. To examine the capability of MSR and the differences between SR and MSR as performance indicator, we applied the SHALSTAB model onto a mountainous watershed in Taiwan. Despite the fact the best model result deduced by SR projects 120 hits over 131 actual landslide sites, this high efficiency is only obtained when unstable cells cover an incredibly high percentage (75%) of the entire watershed. By contrast, the best simulation indicated by MSR projects 83 hits over 131 actual landslide sites while unstable cells only cover 16% of the studied watershed.
Uncertainty in soil physical data at river basin scale
Authors: van der Keur P. , Iversen B. V.
Published: April 2010

Abstract. For hydrological modelling studies at the river basin scale, decision makers need guidance in assessing the implications of uncertain data used by modellers as an input to modelling tools. Simulated solute transport through the unsaturated zone is associated with uncertainty due to spatial variability of soil hydraulic properties and derived hydraulic model parameters. In general for modelling studies at the river basin scale spatially available data at various scales must be aggregated to an appropriate scale. Estimating soil properties at unsampled points by means of geostatistical techniques require reliable information on the spatial structure of soil data. In this paper this information is assessed by reviewing current developments in the field of soil physical data uncertainty and adopting a classification system. Then spatial variability and structure is inspected by reviewing experimental work on determining spatial length scales for soil physical (and soil chemical) data. Available literature on spatial length scales for soil physical- and chemical properties is reviewed and their use in facilitating change of spatial support discussed. Uncertainty associated to the derivation of hydraulic properties from soil physical properties in this context is also discussed.
Estimating spatial mean root-zone soil moisture from point-scale observations
Authors: Teuling A. J. , Uijlenhoet R. , Hupet F. , van Loon E. E. , Troch P. A.
Published: April 2010

Abstract. Root zone soil moisture is a key variable in many land surface hydrology models. Often, however, there is a mismatch in the spatial scales at which models simulate soil moisture and at which soil moisture is observed. The limited spatial support of observations combined with the large spatial variability of the soil moisture field complicates model validation. The increased availability of detailed datasets on space-time variability of root-zone soil moisture allows for a posteriori analysis of the uncertainties in the relation between point-scale observations and the spatial mean. In this paper we analyze three comprehensive datasets from three different regions. We identify different strategies to select observation sites, and we present methods for quantifying the uncertainty that is associated with each strategy. In general there is a large correspondence between the different datasets with respect to the relative uncertainties for the different strategies. For all datasets, the uncertainty can be strongly reduced if some information is available that relates soil moisture at that site to the spatial mean. However this works best if the space-time dynamics of the soil moisture field are known. Selection of the site closest to the spatial mean on a single random date only leads to minor reduction of the uncertainty with respect to the spatial mean over seasonal timescales. Since soil moisture variability is the result of a complex interaction between soil, vegetation, and landscape characteristics, the soil moisture field will be correlated with some of these characteristics. Using available information, we show that the correlation with leaf area index or a wetness coefficient alone is insufficient to predict if a site is representative for the spatial mean soil moisture.
On the importance of including vegetation dynamics in Budyko’s hydrological model
Authors: Donohue R. J. , Roderick M. L. , McVicar T. R.
Published: April 2010

Abstract. The Budyko curve describes the relationship between climate, evapotranspiration and run-off and can be used to model catchment energy and water balances. The curve's underlying framework assumes catchments are at steady-state, a condition dependent on the scales of application, such that its reliability is greatest when applied to large catchments (>10 000 km2) and using long-term averages (≫1 year). At these scales previous experience has shown that the hydrological role of vegetation does not need to be explicitly considered within the framework. By demonstrating how dynamics in the leaf area, photosynthetic capacity and rooting depth of vegetation affect not only annual and seasonal vegetation water use, but also steady-state conditions, we argue that it is necessary to explicitly include vegetation dynamics into the Budyko framework before it is applied at small scales. Such adaptations would extend the framework not only to applications at small timescales and to small catchments but to operational activities relating to vegetation and water management.
Measuring methods for groundwater, surface water and their interactions: a review
Authors: Kalbus E. , Reinstorf F. , Schirmer M.
Published: April 2010

Abstract. Interactions between groundwater and surface water play a critical role in the functioning of riparian ecosystems. In the context of sustainable river basin management it is crucial to understand and quantify exchange processes between groundwater and surface water. Numerous well-known methods exist for parameter estimation and process identification in aquifers and surface waters. The transition zone, however, has only in recent years become a subject of major research interest, and the need has evolved for appropriate methods applicable in this zone. This article provides an overview of the methods that are typically used in aquifers and surface waters when studying interactions and shows the possibilities of application in the transition zone. In addition, methods particularly for use in the transition zone are presented. Considerations for choosing appropriate methods are given including spatial and temporal scales, uncertainties, and limitations in application. It is concluded that a multi-scale approach combining multiple measuring methods may considerably constrain estimates of fluxes between groundwater and surface water.
Self-similar pattern formation and continuous mechanics of self-similar systems
Authors: Dyskin A. V.
Published: April 2010

Abstract. In many cases, the critical state of systems that reached the threshold is characterised by self-similar pattern formation. We produce an example of pattern formation of this kind – formation of self-similar distribution of interacting fractures. The driving force of the fracture system formation is the crack growth due to the action of stress fluctuations. The importance of this mechanism is that even when the fluctuations have zero average the cracks generated by them could growth far beyond the scale of stress fluctuations. Further development of the fracture system is controlled by crack interaction, which in the case of isotropically oriented cracks leads to the emergence of self-similar distributions. The presence of self-similar distributions of fractures in a material poses a challenge in continuum modelling, since this material becomes discontinuous at any scale. We develop a continuum fractal mechanics to model mechanical behaviour of such materials. We introduce a continuous sequence of continua of increasing scales covering this range of scales. The continuum of each scale is specified by the representative volume elements of the corresponding size over which averaging is performed in the process of defining the field variables in the continuum. Subsequently, at each scale the material is modelled by a continuum that hides the cracks of smaller scales while explicitly introducing larger structural elements. The properties assigned to the continuum are effective characteristics accounting for the macroscopic effect of the hidden cracks. Using the developed formalism we investigate the stability of self-similar crack distributions with respect to crack growth and show that while the self-similar distribution of isotropically oriented cracks is stable, the distribution of parallel cracks is not. For the isotropically oriented cracks scaling of permeability is determined. For the crack distribution produced by the action of stress fluctuations permeability increases as cube of crack radius. This property could be used for detecting this specific mechanism of formation of self-similar crack distributions.
Temperatures and precipitation totals over the Russian Far East and Eastern Siberia: long-term variability and its links to teleconnection indices
Authors: Krokhin V. V. , Luxemburg W. M. J.
Published: April 2010

Abstract. The present study examines the spatial-temporal regime of the mean monthly temperature (MMT) and monthly precipitation (MPT) anomalies over the Russian Far East and Eastern Siberia for the period 1949–2003. The original data were analyzed spatially by means of complex principal component analysis and temporally by means of the maximum entropy method and traditional Fourier spectral analysis. The interannual variability in these anomalies can be represented by the single dominant modes. These dominant modes oscillate with periods of about 2–3 yr and 6–8 yr that are accompanied by statistically significant changes in such monthly teleconnection indices, as the Arctic and North Pacific Oscillations.
Modelling subsurface storm flow with the Representative Elementary Watershed (REW) approach: application to the Alzette River Basin
Authors: Zhang G. P. , Savenije H. H. G. , Fenicia F. , Pfister L.
Published: April 2010

Abstract. A new domain, the macropore domain, for describing subsurface storm flow has been introduced to the Representative Elementary Watershed (REW) approach. The mass balance equations have been reformulated and the closure relations associated with subsurface storm flow have been developed. The model code, REWASH, has been revised accordingly. With the revised REWASH, a rainfall-runoff model has been built for the Hesperange catchment, a sub-catchment of the Alzette River Basin. This meso-scale catchment is characterised by fast catchment response to precipitation and subsurface storm flow is one of the dominant runoff generation processes. The model has been evaluated by a multi-criteria approach using both discharge and groundwater table data measured at various locations in the study site. It is demonstrated that subsurface storm flow contributes considerably to stream flow in the study area. Simulation results show that discharges measured along the main river course are well simulated and groundwater dynamics is well captured, suggesting that the model is a useful tool for catchment-scale hydrological analysis.
Measuring forest floor interception in a beech forest in Luxembourg
Authors: Gerrits A. M. J. , Savenije H. H. G. , Hoffmann L. , Pfister L.
Published: April 2010

Abstract. In hydrological models evaporation from interception is often disregarded, combined with transpiration, or taken as a fixed percentage of rainfall. In general interception is not considered to be a significant process in rainfall-runoff modelling. However, it appears that on average interception can amount to 20–50% of the precipitation. Therefore, knowledge about the process of interception is important. Traditional research on interception mainly focuses on canopy interception and almost completely denies forest floor interception, although this is an important mechanism that precedes infiltration or runoff. Forest floor interception consists partly of interception by dry soil, partly of interception by short vegetation (mosses, grasses and creeping vegetation) and partly of interception by litter. This research concentrates on litter interception: to measure its quantities at point scale and subsequently to upscale it to the scale of a hydrotope. A special measuring device has been developed, which consists of a permeable upper basin filled with forest floor and a watertight lower basin. Both are weighed continuously. The device has been tested in the Huewelerbach catchment (Luxembourg). The preliminary measuring results show that the device is working properly. For November 2004, evaporation from interception is calculated to be 34% of the throughfall in the Huewelerbach catchment.
Formation of runoff at the hillslope scale during intense precipitation
Authors: Scherrer S. , Naef F. , Faeh A. O. , Cordery I.
Published: April 2010

Abstract. On 60 m2 hillslope plots at 18 mainly grassland locations in Switzerland rain was applied at rates of 50–100 mm/h for between 3 and 6 h. The generated flows were measured, overland flow near surface and subsurface flow in 0.5–1.3 m below surface. At some locations less than 2% of the rain flowed down the slope either on or below the surface, whereas at some others more than 90% of the rain ran off. At the majority of sites most runoff was overland flow, though at a few sites subsurface flow, usually via macropores was dominant. Data collected during each of 48 high intensity sprinkling experiments were used to distinguish which processes were dominant in each experiment. Which dominant and subsidiary processes occurred depended on interactions between infiltration rate, change in soil water storage and drainage of the soil water. These attributes were often not directly linked to parameters usually considered important like vegetation, slope, soil clay content and antecedent soil moisture. In many cases, process determination was fairly straightforward, indicating the possibility to reliably predict runoff processes at a site. However, at some sites, effects occurred that were not easily recognizable and led to surprising results.
Eco-geomorphology and vegetation patterns in arid and semi-arid regions
Authors: Saco P. M. , Willgoose G. R. , Hancock G. R.
Published: April 2010

Abstract. The interaction between vegetation and hydrologic processes is particularly tight in water-limited environments where a positive-feedback links water redistribution and vegetation. The vegetation of these systems is commonly patterned, that is, arranged in a two phase mosaic composed of patches with high biomass cover interspersed within a low-cover or bare soil component. These patterns are strongly linked to the redistribution of runoff and resources from source areas (bare patches) to sink areas (vegetation patches) and play an important role in controlling erosion. In this paper a new modeling framework that couples landform evolution and dynamic vegetation for water-limited ecosystems is presented. The model explicitly accounts for the dynamics of runon-runoff areas that controls the evolution of vegetation and erosion/deposition patterns in water limited ecosystems. The analysis presented here focuses on the interaction between vegetation patterns, flow dynamics and sediment redistribution for areas with mild slopes where sheet flow occurs and banded vegetation patterns emerge. Model results successfully reproduce the dynamics of both migrating and stationary banded vegetation patterns (commonly known as tiger bush). Modeling results show strong feedbacks effects between vegetation patterns, runoff redistribution and geomorphic changes. The success at generating not only the observed patterns of vegetation but also patterns of runoff and erosion redistribution, which gives rise to modeled microtopography similar to that observed in several field sites, suggests that the hydrologic and erosion mechanisms represented in the model are correctly capturing the essential processes driving these ecosystems.
Modeling and analysis of collective management of water resources
Authors: Tilmant A. , van der Zaag P. , Fortemps P.
Published: April 2010

Abstract. Integrated Water Resources Management (IWRM) recommends, among other things, that the management of water resources systems be carried out at the lowest appropriate level in order to increase the transparency, acceptability and efficiency of the decision-making process. Empowering water users and stakeholders transforms the decision-making process by enlarging the number of point of views that must be considered as well as the set of rules through which decisions are taken. This paper investigates the impact of different group decision-making approaches on the operating policies of a water resource. To achieve this, the water resource allocation problem is formulated as an optimization problem which seeks to maximize the aggregated satisfaction of various water users corresponding to different approaches to collective choice, namely the utilitarian and the egalitarian ones. The optimal operating policies are then used in simulation and compared. The concepts are illustrated with a multipurpose reservoir in Chile. The analysis of simulation results reveals that if this reservoir were to be managed by its water users, both approaches to collective choice would yield significantly different operating policies. The paper concludes that the transfer of management to water users must be carefully implemented if a reasonable trade-off between equity and efficiency is to be achieved.
Assessing the model performance of an integrated hydrological and biogeochemical model for discharge and nitrate load predictions
Authors: Pohlert T. , Breuer L. , Huisman J. A. , Frede H.-G.
Published: April 2010

Abstract. In this study, we evaluate the performance of the SWAT-N model, a modified version of the widely used SWAT version, for discharge and nitrate predictions at the mesoscale Dill catchment for a 5-year period. The underlying question is, whether the model efficiency is sufficient for scenario analysis of land-use changes on both water quantity and quality. The Shuffled Complex Evolution (SCE-UA) algorithm is used to calibrate the model for daily discharge at the catchments outlet. Model performance is assessed with a split-sampling as well as a proxy-basin test using recorded hydrographs of four additional gauges located within the catchment. The efficiency regarding nitrate load simulation is assessed without further calibration on a daily, log-daily, weekly, and monthly basis as compared to observations derived from an intensive sampling campaign conducted at the catchments outlet. A new approach is employed to test the spatial consistency of the model, where simulated longitudinal profiles of nitrate concentrations were compared with observed longitudinal profiles. It is concluded that the model efficiency of SWAT-N is sufficient for the assessment of scenarios for daily discharge predictions. SWAT-N can be employed without further calibration for nitrate load simulations on both a weekly and monthly basis with an acceptable degree of accuracy. However, the model efficiency for daily nitrate load is insufficient, which can be attributed to both data uncertainty (i.e. point-source effluents and actual farming practise) as well as structural errors. The simulated longitudinal profiles meet the observations reasonably well, which suggests that the model is spatially consistent.
Rainfall threshold for hillslope outflow: an emergent property of flow pathway connectivity
Authors: Lehmann P. , Hinz C. , McGrath G. , Tromp-van Meerveld H.-J. , McDonnell J. J.
Published: April 2010

Abstract. Nonlinear relations between rain input and hillslope outflow are common observations in hillslope hydrology field studies. In this paper we use percolation theory to model the threshold relationship between rainfall amount and outflow and show that this nonlinear relationship arises from simple linear processes at the smaller scale. When the rainfall amount exceeds a threshold value, the underlying elements become connected and water flows out of the base of the hillslope. The percolation approach shows how random variations in storage capacity and connectivity at the small spatial scale cause a threshold relationship between rainstorm amount and hillslope outflow. As a test case, we applied percolation theory to the well characterized experimental hillslope at the Panola Mountain Research Watershed. Analyzing the measured rainstorm events and the subsurface stormflow with percolation theory, we could determine the effect of bedrock permeability, spatial distribution of soil properties and initial water content within the hillslope. Our results indicate that the measured variation in the relationship between rainstorm amount and subsurface flow is dominated by the initial moisture deficit, the loss of free water to the bedrock, the limited size of the system and by the connectivity due to macropores. The values of the model parameters were in agreement with measured values of soil depth distribution and water saturation.
Uncertainties in selected surface water quality data
Authors: Rode M. , Suhr U.
Published: April 2010

Abstract. Monitoring of surface waters is primarily done to detect the status and trends in water quality and to identify whether observed trends arise form natural or anthropogenic causes. Empirical quality of surface water quality data is rarely certain and knowledge of their uncertainties is essential to assess the reliability of water quality models and their predictions. The objective of this paper is to assess the uncertainties in selected surface water quality data, i.e. suspended sediment, nitrogen fraction, phosphorus fraction, heavy metals and biological compounds. The methodology used to structure the uncertainty is based on the empirical quality of data and the sources of uncertainty in data (van Loon et al., 2006). A literature review was carried out including additional experimental data of the Elbe river. All data of compounds associated with suspended particulate matter have considerable higher sampling uncertainties than soluble concentrations. This is due to high variability's within the cross section of a given river. This variability is positively correlated with total suspended particulate matter concentrations. Sampling location has also considerable effect on the representativeness of a water sample. These sampling uncertainties are highly site specific. The estimation of uncertainty in sampling can only be achieved by taking at least a proportion of samples in duplicates. Compared to sampling uncertainties measurement and analytical uncertainties are much lower. Instrument quality can be stated well suited for field and laboratory situations for all considered constituents. Analytical errors can contribute considerable to the overall uncertainty of surface water quality data. Temporal autocorrelation of surface water quality data is present but literature on general behaviour of water quality compounds is rare. For meso scale river catchments reasonable yearly dissolved load calculations can be achieved using biweekly sample frequencies. For suspended sediments none of the methods investigated produced very reliable load estimates when weekly concentrations data were used. Uncertainties associated with loads estimates based on infrequent samples will decrease with increasing size of rivers.
The use of meteorological analogues to account for LAM QPF uncertainty
Authors: Diomede T. , Nerozzi F. , Paccagnella T. , Todini E.
Published: April 2010

Abstract. Flood predictions issued employing quantitative precipitation forecasts (QPFs) provided by deterministic models do not account for the uncertainty in the outcomes. A probabilistic approach to QPF seems to be indispensable to obtain different future flow scenarios that allow to manage the flood accounting for the variability of phenomena and the uncertainty associated with an hydrological forecast. A new approach based on a search for past situations (analogues), similar to previous and current day in terms of different meteorological fields over Western Europe and East Atlantic, has been developed to determine an ensemble of hourly quantitative precipitation forecasts for the Reno river basin, a medium-sized catchment in northern Italy. A statistical analysis, performed over an hydro-meteorological archive collecting ECMWF analyses at 12:00 UTC relative to the autumn seasons ranging from 1990 to 2000 and the corresponding precipitation measurements recorded by the raingauges spread over the catchment of interest, has underlined that the combination of geopotential at 500 hPa and vertical velocity at 700 hPa provides a better estimation of precipitation. The analogue-based ensemble prediction has to be considered not alternative but complementary with the deterministic QPF provided by a numerical model, even in view of a joint employment to improve real-time flood forecasting. In the present study, the analogue-based QPFs and the precipitation forecast provided by the Limited Area Model LAMBO have been used as different input to the distributed rainfall-runoff model TOPKAPI, thus generating, respectively, an ensemble of discharge forecasts, which provides a confidence interval for the predicted streamflow, and a deterministic discharge forecast taken as an error affected "measurement'' of the future flow, which does not convey any quantification of the forecast uncertainty. To make more informative the hydrological prediction, the ensemble spread could be regarded as a measure of the uncertainty of the deterministic forecast.
Assessment of impacts of climate change on water resources – a case study of the Great Lakes of North America
Authors: McBean E. , Motiee H.
Published: April 2010

Abstract. Historical trends in precipitation, temperature, and streamflows in the Great Lakes are examined using regression analysis and Mann-Kendall statistics, with the result that many of these variables demonstrate statistically significant increases ongoing for a six decade period. Future precipitation rates as predicted using fitted regression lines are compared with scenarios from Global Climate Change Models (GCMs) and demonstrate similar forecast predictions for Lake Superior. Trend projections from historical data are, however, higher than GCM predictions for Michigan/Huron. Significant variability in predictions, as developed from alternative GCMs, is noted. Given the general agreement as derived from very different procedures, predictions extrapolated from historical trends and from GCMs, there is evidence that hydrologic changes in the Great Lakes Basin are likely the result of climate change.
Uncertainty analysis of hydrological ensemble forecasts in a distributed model utilising short-range rainfall prediction
Authors: Cluckie I. D. , Xuan Y. , Wang Y.
Published: April 2010

Abstract. Advances in meso-scale numerical weather predication make it possible to provide rainfall forecasts along with many other data fields at increasingly higher spatial resolutions. It is currently possible to incorporate high-resolution NWPs directly into flood forecasting systems in order to obtain an extended lead time. It is recognised, however, that direct application of rainfall outputs from the NWP model can contribute considerable uncertainty to the final river flow forecasts as the uncertainties inherent in the NWP are propagated into hydrological domains and can also be magnified by the scaling process. As the ensemble weather forecast has become operationally available, it is of particular interest to the hydrologist to investigate both the potential and implication of ensemble rainfall inputs to the hydrological modelling systems in terms of uncertainty propagation. In this paper, we employ a distributed hydrological model to analyse the performance of the ensemble flow forecasts based on the ensemble rainfall inputs from a short-range high-resolution mesoscale weather model. The results show that: (1) The hydrological model driven by QPF can produce forecasts comparable with those from a raingauge-driven one; (2) The ensemble hydrological forecast is able to disseminate abundant information with regard to the nature of the weather system and the confidence of the forecast itself; and (3) the uncertainties as well as systematic biases are sometimes significant and, as such, extra effort needs to be made to improve the quality of such a system.
Theoretical investigation of process controls upon flood frequency: role of thresholds
Authors: Struthers I. , Sivapalan M.
Published: April 2010

Abstract. Traditional statistical approaches to flood frequency inherently assume homogeneity and stationarity in the flood generation process. This study illustrates the impact of heterogeneity associated with threshold non-linearities in the storage-discharge relationship associated with the rainfall-runoff process upon flood frequency behaviour. For a simplified, non-threshold (i.e. homogeneous) scenario, flood frequency can be characterised in terms of rainfall frequency, the characteristic response time of the catchment, and storm intermittency, modified by the relative strength of evaporation. The flood frequency curve is then a consistent transformation of the rainfall frequency curve, and could be readily described by traditional statistical methods. The introduction of storage thresholds, namely a field capacity storage and a catchment storage capacity, however, results in different flood frequency "regions" associated with distinctly different rainfall-runoff response behaviour and different process controls. The return period associated with the transition between these regions is directly related to the frequency of threshold exceedence. Where threshold exceedence is relatively rare, statistical extrapolation of flood frequency on the basis of short historical flood records risks ignoring this heterogeneity, and therefore significantly underestimating the magnitude of extreme flood peaks.
Comparing sensitivity analysis methods to advance lumped watershed model identification and evaluation
Authors: Tang T. , Reed P. , Wagener T. , van Werkhoven K.
Published: April 2010

Abstract. This study tested four sensitivity analysis methods: (1) local analysis using parameter estimation software (PEST), (2) regional sensitivity analysis (RSA), (3) analysis of variance (ANOVA), and (4) Sobol's method to identify sensitivity tools that will advance our understanding of lumped hydrologic models for the purposes of model improvement, calibration efficiency and improved measurement schemes. The methods' relative efficiencies and effectiveness have been analyzed and compared. These four sensitivity methods were applied to the lumped Sacramento soil moisture accounting model (SAC-SMA) coupled with SNOW-17. Results from this study characterize model sensitivities for two medium sized watersheds within the Juniata River Basin in Pennsylvania, USA. Comparative results for the 4 sensitivity methods are presented for a 3-year time series with 1 h, 6 h, and 24 h time intervals. The results of this study show that model parameter sensitivities are heavily impacted by the choice of analysis method as well as the model time interval. Differences between the two adjacent watersheds also suggest strong influences of local physical characteristics on the sensitivity methods' results. This study also contributes a comprehensive assessment of the repeatability, robustness, efficiency, and ease-of-implementation of the four sensitivity methods. Overall ANOVA and Sobol's method were shown to be superior to RSA and PEST. Relative to one another, ANOVA has reduced computational requirements and Sobol's method yielded more robust sensitivity rankings.