bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrochemical heterogeneity in an upland catchment: further characterisation of the spatial, temporal and depth variations in soils, streams and groundwaters of the Plynlimon forested catchment, Wales
Authors: Shand P. , Haria A. H. , Neal C. , Griffiths K. J. , Gooddy D. C. , Dixon A. J. , Hill T. , Buckley D. K. , Cunningham J. E.
Published: April 2010

Abstract. The heterogeneous nature of upland hard-rock catchments in terms of geology, geomorphology, superficial deposits, soil type and land use gives rise to a range of hydrochemical characteristics in stream waters. This is further complicated by the large and often rapid changes in stream flow typical of storm events. The sources of solutes and flow pathways in hard-rock catchments are still poorly understood, in particular the role of bedrock groundwater. Spatial variations in water chemistry are presented for stream waters, soils and groundwaters in the forested Plynlimon catchment of Wales, UK. The results highlight a large degree of spatial heterogeneity in each of these systems. This has major implications for the application of end-member mixing analysis and presents serious problems for modelling in scaling up from study sites to catchment scale. However, such data provide important constraints on sources, flow pathways and residence times within individual catchment compartments, knowledge of which is essential for understanding how such catchments function. The characterisation of sub-surface waters in upland catchments requires a great deal of care during sampling as well as high spatial and temporal resolution of sampling, and further work is required to characterise the Plynlimon catchments fully. Nevertheless, the presence of an active and highly stratified groundwater system is considered important as a source of solutes and water to streams. It also provides a storage medium that is likely to make a major contribution to explaining the strongly damped rainfall Cl and d2H signals measured in the streams.
High-resolution phosphorus transfers at the catchment scale: the hidden importance of non-storm transfers
Authors: Jordan P. , Arnscheidt J. , McGrogan H. , McCormick S.
Published: April 2010

Abstract. High-resolution measurements of total phosphorus (TP) concentrations in a stream draining a 5 km2 agricultural catchment (a sub-catchment of Lough Neagh in Northern Ireland) were made every 10 min by continuous flow instrumentation using new homogenisation, digestion and colorimetric phases. Concurrently, rainfall and stream discharge data were collected at 5 and 15 min intervals. Major P flushing episodes during storm events peaked on the rising limbs of storm hydrographs. A period of baseflow also indicated the importance of other sources that maintain the stream in a eutrophic state between storm events. These data provide insights into catchment processes that conform to definite patterns that, in a coarser sampling regime, might ordinarily be attributed to sampling and analytical "noise".
Increasing silicon concentrations in Bohemian Forest lakes
Authors: Veselý J. , Majer V. , Kopácek J. , Safanda J. , Norton S. A.
Published: April 2010

Abstract. Long-term trends of dissolved silicon (Si) concentrations in five glacial lakes in the Bohemian Forest, Czech Republic, recovering from acidification show higher mobility of Si from the soil to surface waters despite lower atmospheric deposition of acids. Si increased by 0.95 to 1.95 µmol yr-1 (36 to 51%) from 1986-2004 and with increasing pH. A change in soil solution conditions because of a sharp decrease in acidic deposition has led to marked decline in Al mobility and to considerable decreases in dissolved Al, especially Al3+. The increase in Si may be related to: (1) unblocking of the inhibitory effect of dissolved Al on weathering of aluminosilicates, (2) biogenic opal (phytoliths) dissolving faster, and/or (3) lower Si precipitation as secondary aluminosilicates in soil. The change in Al speciation on the dissolution rate of biogenic silica is critical. A lack of change in Si at sites outside central Europe may be explained by small or no decline in mobility of dissolved Al. The effect of a long-term increase in temperature was probably minor.
Transpiration of montane Pinus sylvestris L. and Quercus pubescens Willd. forest stands measured with sap flow sensors in NE Spain
Authors: Poyatos R. , Llorens P. , Gallart F.
Published: April 2010

Abstract. Stand transpiration was measured during the 2003 and 2004 growing seasons using heat dissipation sap flow sensors in a Scots pine (Pinus sylvestris L.) and a pubescent oak (Quercus pubescens Willd.) forest located in a montane area of the Eastern Pyrenees (NE Spain). The first aim of the study was to assess the differences in quantitative estimates of transpiration (Ec) and the response to evaporative demand of the two stands. Over the studied period of 2003, characterised by a severe drought episode during the summer, the oak stand Ec was only 110mm compared to the 239 mm transpired by the Scots pine stand, although the ratio of transpiration to reference evapotranspiration (Ec/ET0) in the oak stand compares well with the expected values predicted for low leaf area index (LAI) oak forests in southern Europe. Scots pine showed a strong reduction in Ec/ET0 as the drought developed, whereas pubescent oak was less affected by soil moisture deficits in the upper soil. As a second objective, and given the contrasting meteorological conditions between 2003 and 2004 summer periods, the interanual variability of transpiration was studied in the Scots pine plot. Rainfall during the summer months (June-September) in 2003 was almost 40% less than in the same interval in 2004. Accordingly, transpiration was also reduced about 25% in 2003. Finally, Scots pine data from 2003 and 2004 was used to calibrate a simple transpiration model using ET0 and soil moisture deficit (SMD) as input variables, and implicitly including stomatal responses to high vapour pressure deficits (Dδ) and soil water status.
A Bayesian spatial assimilation scheme for snow coverage observations in a gridded snow model
Authors: Kolberg S. , Rue H. , Gottschalk L.
Published: April 2010

Abstract. A spatial probability distribution of the variables in a parametric snow depletion curve (SDC) is tailored to the assimilation of satellite snow cover data into a gridded hydrological model. The assimilation is based on Bayes' theorem, in which the proposed distribution represents the a priori information about the SDC variables. From the prior gridded maps of snow storage and accumulated melt depth, the elevation gradients and the degree-day factor are separated out, creating elevation-normalised surfaces of snow storage and degree-day sum. Because the small-scale variability linked to elevation is removed, these surfaces can be described by prior distribution models with a strong spatial dependency structure. This reduction of spatial uniqueness in the prior distribution greatly increases the informational value of the remotely sensed snow coverage data. The assimilation is evaluated in a 2400 km2 mountainous region in central Norway (61° N, 9° E), based on two Landsat 7 ETM+ images evaluated at 1 km2 scale. An image acquired on 11 May, a week before the peak flood, removes 78% of the variance in the remaining snow storage. Even an image from 4 May, less than a week after the melt onset, reduces this variance by 53%. Including observed discharge in the updating information improves the 4 May results, but has weak effect on 11 May. Estimated elevation gradients are shown to be sensitive to informational deficits occurring at high altitude, where snowmelt has not yet started. Caution is therefore required when using early images.
Development and validation of the global map of irrigation areas
Authors: Siebert S. , Döll P. , Hoogeveen J. , Faures J.-M. , Frenken K. , Feick S.
Published: April 2010

Abstract. A new version of a digital global map of irrigation areas was developed by combining irrigation statistics for 10825 sub-national statistical units and geo-spatial information on the location and extent of irrigation schemes. The map shows the percentage of each 5 arc minute by 5 arc minute cell that was equipped for irrigation around the year 2000. It is thus an important data set for global studies related to water and land use. This paper describes the data set and the mapping methodology and gives, for the first time, an estimate of the map quality at the scale of countries, world regions and the globe. Two indicators of map quality were developed for this purpose, and the map was compared to irrigated areas as derived from two remote sensing based global land cover inventories. We plan to further improve that data set; therefore comments, information and data that might contribute to that effort are highly welcome.
A distributed continuous simulation model to identify critical source areas of phosphorus at the catchment scale: model description
Authors: Koo B. K. , Dunn S. M. , Ferrier R. C.
Published: April 2010

Abstract. This paper presents CAMEL (Chemicals from Agricultural Management and Erosion Losses), a distributed continuous simulation model to simulate daily phosphorus (P) transformations and transport at the catchment scale. CAMEL is a process-oriented mass-balance model that is based on both analytical and numerical approaches. In the model, a catchment is represented using a network of square grid cells each of which is comprised of various storages of water, sediment and P. Most of hydrological processes, soil erosion, sediment transport, and P transformations and transport are described using process-based equations. The P transformations between five P storages (active organic, stable organic, labile, active inorganic, and stable organic) are described using first-order kinetic equations. A comprehensive cascade routing scheme is used to simulate P retention and transport along the channel system. Dissolved P is also transported by groundwater flows, described using a two-dimensional Boussinesq equation. CAMEL simulates both surface and subsurface processes explicitly and therefore is suitable for catchment-scale applications. The distributed, process-oriented structure of CAMEL enables the model to be used for identifying critical source areas of P at the catchment-scale. CAMEL is also computationally efficient, allowing for long-term scale applications.
Distance in spatial interpolation of daily rain gauge data
Authors: Ahrens B.
Published: April 2010

Abstract. Spatial interpolation of rain gauge data is important in forcing of hydrological simulations or evaluation of weather predictions, for example. The spatial density of available data sites is often changing with time. This paper investigates the application of statistical distance, like one minus common variance of time series, between data sites instead of geographical distance in interpolation. Here, as a typical representative of interpolation methods the inverse distance weighting interpolation is applied and the test data is daily precipitation observed in Austria. Choosing statistical distance instead of geographical distance in interpolation of an actually available coarse observation network yields more robust interpolation results at sites of a denser network with actually lacking observations. The performance enhancement is in or close to mountainous terrain. This has the potential to parsimoniously densify the currently available observation network. Additionally, the success further motivates search for conceptual rain-orography interaction models as components of spatial rain interpolation algorithms in mountainous terrain.
Multi-objective calibration of a surface water-groundwater flow model in an irrigated agricultural region: Yaqui Valley, Sonora, Mexico
Authors: Schoups G. , Lee Addams C. , Gorelick S. M.
Published: April 2010

Abstract. Multi-objective optimization was used to calibrate a regional surface water-groundwater model of the Yaqui Valley, a 6800 km2 irrigated agricultural region located along the Sea of Cortez in Sonora, Mexico. The main advantage of the method is that it accounts for both parameter and model structural uncertainty. In this case, results show that the effect of including the process of bare soil evaporation is significantly greater than the effects of parameter uncertainty. Furthermore, by treating the different objectives independently, a better identification of the model parameters is achieved compared to a single-objective approach, since the various objectives are sensitive to different parameters. The simulated water balance shows that 15–20% of the water that enters the irrigation canals is lost by seepage to groundwater. The main discharge mechanisms in the Valley are crop evapotranspiration (53%), non-agricultural evapotranspiration and bare soil evaporation (19%), surface drainage to the Sea of Cortez (15%), and groundwater pumping (9%). In comparison, groundwater discharge to the estuary was relatively insignificant (less than 1%). The model was further refined by identifying zonal Kv and Kh values based on a spatial analysis of the model residuals. This is the first comprehensive flow model of this important surface water-aquifer system, and it will be used in future work to identify optimal groundwater management strategies.
Top-kriging – geostatistics on stream networks
Authors: Skøien J. O. , Merz R. , Blöschl G.
Published: April 2010

Abstract. We present Top-kriging, or topological kriging, as a method for estimating streamflow-related variables in ungauged catchments. It takes both the area and the nested nature of catchments into account. The main appeal of the method is that it is a best linear unbiased estimator (BLUE) adapted for the case of stream networks without any additional assumptions. The concept builds on the work of Sauquet et al. (2000) and extends it in a number of ways. We test the method for the case of the specific 100-year flood for two Austrian regions. The method provides more plausible and, indeed, more accurate estimates than Ordinary Kriging. Top-kriging also provides estimates of the uncertainty of the variable of interest. On the main stream the estimated uncertainties are smallest and they gradually increase as one moves towards the headwaters. The method as presented here is able to exploit the information contained in short records by accounting for the uncertainty of each gauge. We suggest that Top-kriging can be used for spatially interpolating a range of streamflow-related variables including mean annual discharge, flood characteristics, low flow characteristics, concentrations, turbidity and stream temperature.
Empirical Mode Decomposition in 2-D space and time: a tool for space-time rainfall analysis and nowcasting
Authors: Sinclair S. , Pegram G. G. S.
Published: April 2010

Abstract. A data-driven method for extracting information, at temporally predictable scales, from spatial rainfall data (as measured by radar/satellite) is described, which extends the Empirical Mode Decomposition (EMD) algorithm into two dimensions. The EMD technique is used here to separate spatial rainfall data into a sequence of high through to low frequency components. This process is equivalent to a low-pass spatial filter, but based on the observed properties of the data rather than the predefined basis functions used in traditional Fourier or Wavelet decompositions. It has been suggested in the literature that the lower frequency components of spatial rainfall data exhibit greater temporal persistence than the higher frequency ones. This idea is explored here in the context of Empirical Mode Decomposition, to prepare rainfall data for nowcasts based on the temporal evolution of the lower frequency components. The paper focuses on the implementation and development of the two-dimensional extension to the EMD algorithm and it's application to radar rainfall data, as well as examining temporal persistence in the data at different spatial scales.
Constraints of artificial neural networks for rainfall-runoff modelling: trade-offs in hydrological state representation and model evaluation
Authors: de Vos N. J. , Rientjes T. H. M.
Published: April 2010

Abstract. The application of Artificial Neural Networks (ANNs) on rainfall-runoff modelling needs to be researched more extensively in order to appreciate and fulfil the potential of this modelling approach. This paper reports on the application of multi-layer feedforward ANNs for rainfall-runoff modelling in the Geer catchment (Belgium) using both daily and hourly data. The good daily forecast results indicate that ANNs can be considered alternatives for traditional rainfall-runoff modelling approaches. However, investigation of the forecasts based on hourly data reveal a constraint that has hitherto been neglected by hydrologists. A timing error occurs due to a dominating autoregressive component that is introduced by using previous runoff values as ANN model input. The reason for the popular practice of using these previous runoff data is that this information indirectly represents the hydrological state of the catchment. Two possible solutions to this timing problem are discussed. Firstly, several alternatives for representation of the hydrological state are presented: moving averages over the previous discharge and over the previous rainfall, and the output of the simple GR4J model component for soil moisture. A combination of these various hydrological state representators produces good results in terms of timing, but the overall goodness of fit is not as good as the simulations with previous runoff data. Secondly, the use of a combination of multiple measures of model performance during ANN training is suggested, since not all differences between modelled and observed hydrograph characteristics such as timing, volume, and absolute values can be adequately expressed by a single performance measure. The possible undervaluation of timing errors by the commonly-used squared-error-based functions is a clear example of this inability.
Spatial and temporal patterns of land surface fluxes from remotely sensed surface temperatures within an
Authors: McCabe M. F. , Kalma J. D. , Franks S. W.
Published: April 2010

Abstract. Characterising the development of evapotranspiration through time is a difficult task, particularly when utilising remote sensing data, because retrieved information is often spatially dense, but temporally sparse. Techniques to expand these essentially instantaneous measures are not only limited, they are restricted by the general paucity of information describing the spatial distribution and temporal evolution of evaporative patterns. In a novel approach, temporal changes in land surface temperatures, derived from NOAA-AVHRR imagery and a generalised split-window algorithm, are used as a calibration variable in a simple land surface scheme (TOPUP) and combined within the Generalised Likelihood Uncertainty Estimation (GLUE) methodology, to provide estimates of areal evapotranspiration at the pixel scale. Such an approach offers an innovative means of transcending the patch or landscape scale of SVAT type models, to spatially distributed estimates of model output. The resulting spatial and temporal patterns of land surface fluxes and surface resistance are used to more fully understand the hydro-ecological trends observed across a study catchment in eastern Australia. The modelling approach is assessed by comparing predicted cumulative evapotranspiration values with surface fluxes determined from Bowen ratio systems and using auxiliary information such as in-situ soil moisture measurements and depth to groundwater to corroborate observed responses.
Influence of solar activity on hydrological processes
Authors: Pérez-Peraza J. , Leyva-Contreras A. , Valdés-Barrón M. , Libin I. , Yudakhin K. , Jaani A.
Published: April 2010

Abstract. The relationship between solar activity and the water volumes of lakes is searched here by means of correlational and spectral analysis methods. The level of two lakes, Pátzcuaro in México and Tchudskoye in Russia, together with solar activity indexes are used for the analysis. It is found that the source of the oscillation mechanism of the level of those lakes is the solar activity cycle through its influence on the magnetosphere and the terrestrial atmosphere. The present study allows for the development of long-period prognostic of water volumes of big lakes.
Chemical characterization of fog and rain water collected at the eastern Andes cordillera
Authors: Beiderwieden E. , Wrzesinsky T. , Klemm O.
Published: April 2010

Abstract. During a three month period in 2003 and 2004, the chemistry of fog and rainwater were studied at the "El Tiro" site in a tropical mountain forest ecosystem in Ecuador, South America. The fogwater samples were collected using a passive fog collector, and for the rain water, a standard rain sampler was employed. For all samples, electric conductivity, pH, and the concentrations of NH4+, K+, Na+, Ca2+, Mg2+, Cl-, NO3-, PO43-, and SO42-, were measured. For each fog sample, a 5 day back trajectory was calculated by the use of the HYSPLIT model. Two types of trajectories occurred. One type was characterized by advection of air masses from the East over the Amazonian basin, the other trajectory arrived one from the West after significant travel time over the Pacific Ocean. We found considerably higher ion concentrations in fogwater samples than in rain samples. Median pH values are 4.58 for fog water, and 5.26 for the rain samples, respectively. The median electric conductivity was 23 µS cm-1 for the fog and 6 µS cm-1 for the rain. The concentrations of all analysed ions were relatively low compared to other mountainous sites (Weathers et al., 1988; Elias et al., 1995; Schemenauer et al., 1995; Wrzesinsky and Klemm, 2000; Zimmermann and Zimmermann, 2002). The continent samples exhibit higher concentrations of most ions as compared to the pacific samples.
Curvature distribution within hillslopes and catchments and its effect on the hydrological response
Authors: Bogaart P. W. , Troch P. A.
Published: April 2010

Abstract. Topographic convergence and divergence are first order controls on the hillslope and catchment hydrological response, as evidenced by similarity parameter analyses. Hydrological models often do not take convergence as measured by contour curvature directly into account; instead they use comparable measures like the topographic index or the hillslope width function. This paper focusses on the question how hillslope width functions and contour curvature are related within the Plynlimon catchments, Wales. It is shown that the total width function of all hillslopes suggest that the catchments are overall divergent, which is in contrast to the perception that catchments should be overall convergent. This so-called convergence paradox is explained by the effect of skewed curvature distributions and extreme curvatures near the channel network. The hillslope-storage Boussinesq (hsB) model is used to asses the effect of within-hillslope convergence variability on the hydrological response. It is concluded that this effect is small, even when the soil saturation threshold is exceeded. Also described in this paper is a novel algorithm to compute flow path lengths on hillslopes towards the drainage network, using the multiple-flow-direction method.
Pattern, process, and function in landscape ecology and catchment hydrology – how can quantitative landscape ecology support predictions in ungauged basins (PUB)?
Authors: Schröder B.
Published: April 2010

Abstract. The understanding of landscape controls on the natural variability of hydrologic processes is an important research question of the PUB (Predictions in Ungauged Basins) initiative. Quantitative landscape ecology, which aims at understanding the relationships of patterns and processes in dynamic heterogeneous landscapes, may greatly contribute to this research effort by assisting the coupling of ecological and hydrological models. The present paper reviews the currently emerging rapprochement between ecological and hydrological research. It points out some common concepts and future research needs in both areas in terms of pattern, process and function analysis and modelling. Focusing on riverine landscapes, the interrelation between ecological and hydrological processes are illustrated. Two further complementary examples show how both disciplines can provide valuable information for each other. I close with some visions about promising (landscape) ecological concepts that may help advancing one of the most challenging tasks in catchment hydrology: Predictions in ungauged basins.
Klinkenberg effect for gas permeability and its comparison to water permeability for porous sedimentary rocks
Authors: Tanikawa W. , Shimamoto T.
Published: April 2010

Abstract. The difference between gas and water permeabilities is significant not only for solving gas-water two-phase flow problems, but also for quick measurements of permeability using gas as pore fluid. We have measured intrinsic permeability of sedimentary rocks from the Western Foothills of Taiwan, using nitrogen gas and distilled water as pore fluids, during several effective-pressure cycling tests at room temperature. The observed difference in gas and water permeabilities has been analyzed in view of the Klinkenberg effect. This effect is due to slip flow of gas at pore walls which enhances gas flow when pore sizes are very small. Experimental results show (1) that gas permeability is larger than water permeability by several times to one order of magnitude, (2) that gas permeability increases with increasing pore pressure, and (3) that water permeability slightly increases with increasing pore-pressure gradient across the specimen. The results (1) and (2) can be explained by Klinkenberg effect quantitatively with an empirical power law for Klinkenberg constant. Thus water permeability can be estimated from gas permeability. The Klinkenberg effect is important when permeability is lower than 10−18 m2 and at low differential pore pressures, and its correction is essential for estimating water permeability from the measurement of gas permeability. A simple Bingham-flow model of pore water can explain the overall trend of the result (3) above. More sophisticated models with a pore-size distribution and with realistic rheology of water film is needed to account for the observed deviation from Darcy's law.
Validation of MODIS snow cover images over Austria
Authors: Parajka J. , Blöschl G.
Published: April 2010

Abstract. This study evaluates the Moderate Resolution Imaging Spectroradiometer (MODIS) snow cover product over the territory of Austria. The aims are (a) to analyse the spatial and temporal variability of the MODIS snow product classes, (b) to examine the accuracy of the MODIS snow product against in situ snow depth data, and (c) to identify the main factors that may influence the MODIS classification accuracy. We use daily MODIS grid maps (version 4) and daily snow depth measurements at 754 climate stations in the period from February 2000 to December 2005. The results indicate that, on average, clouds obscured 63% of Austria, which may significantly restrict the applicability of the MODIS snow cover images to hydrological modelling. On cloud-free days, however, the classification accuracy is very good with an average of 95%. There is no consistent relationship between the classification errors and dominant land cover type and local topographical variability but there are clear seasonal patterns to the errors. In December and January the errors are around 15% while in summer they are less than 1%. This seasonal pattern is related to the overall percentage of snow cover in Austria, although in spring, when there is a well developed snow pack, errors tend to be smaller than they are in early winter for the same overall percent snow cover. Overestimation and underestimation errors balance during most of the year which indicates little bias. In November and December, however, there appears to exist a tendency for overestimation. Part of the errors may be related to the temporal shift between the in situ snow depth measurements (07:00 a.m.) and the MODIS acquisition time (early afternoon).
Investigation of dominant hydrological processes in a tropical catchment in a monsoonal climate via the downward approach
Authors: Montanari L. , Sivapalan M. , Montanari A.
Published: April 2010

Abstract. This study explores the dominant processes that may be responsible for the observed streamflow response in Seventeen Mile Creek, a tropical catchment located in a monsoonal climate in Northern Territory, Australia. The hydrology of this vast region of Australia is little understood due to the low level of information and gauging that is available. Any insights that can be gained from the few well gauged catchments that exist can be valuable for predictions and water resource assessments in other poorly gauged or ungauged catchments in the region. To this end, the available rainfall and runoff data from Seventeen Mile Creek catchment are analyzed through the systematic and progressive development and testing of rainfall-runoff models of increasing complexity, by following the "downward" or "top-down" approach. At the end a multiple bucket model (4 buckets in parallel) is developed. Modelling results suggest that the catchment's soils and the landscape in general have a high storage capacity, generating a significant fraction of delayed runoff, whereas saturation excess overland flow occurs only after heavy rainfall events. The sensitivity analyses carried out with the model with regard to soil depth and temporal rainfall variability reveal that total runoff from the catchment is more sensitive to rainfall variations than to soil depth variations, whereas the partitioning into individual components of runoff appears to be more influenced by soil depth variations. The catchment exhibits considerable inter-annual variability in runoff volumes and the greatest determinant of this variability turns out to be the seasonality of the climate, the timing of the wet season, and temporal patterns of the rainfall. The water balance is also affected by the underlying geology, nature of the soils and the landforms, and the type, density and dynamics of vegetation, although, information pertaining to these is lacking.
Detecting long-memory: Monte Carlo simulations and application to daily streamflow processes
Authors: Wang W. , van Gelder P. H. A. J. M. , Vrijling J. K. , Chen X.
Published: April 2010

Abstract. The Lo's R/S tests (Lo, 1991), GPH test (Geweke and Porter-Hudak, 1983) and the maximum likelihood estimation method implemented in S-Plus (S-MLE) are evaluated through intensive Mote Carlo simulations for detecting the existence of long-memory. It is shown that, it is difficult to find an appropriate lag q for Lo's test for different AR and ARFIMA processes, which makes the use of Lo's test very tricky. In general, the GPH test outperforms the Lo's test, but for cases where there is strong autocorrelations (e.g., AR(1) processes with φ=0.97 or even 0.99), the GPH test is totally useless, even for time series of large data size. Although S-MLE method does not provide a statistic test for the existence of long-memory, the estimates of d given by S-MLE seems to give a good indication of whether or not the long-memory is present. Data size has a significant impact on the power of all the three methods. Generally, the power of Lo's test and GPH test increases with the increase of data size, and the estimates of d with GPH test and S-MLE converge with the increase of data size. According to the results with the Lo's R/S test (Lo, 1991), GPH test (Geweke and Porter-Hudak, 1983) and the S-MLE method, all daily flow series exhibit long-memory. The intensity of long-memory in daily streamflow processes has only a very weak positive relationship with the scale of watershed.
Estimation of flooded area in the Bahr El-Jebel basin using remote sensing techniques
Authors: Shamseddin M. A. H. , Hata T. , Tada A. , Bashir M. A. , Tanakamaru T.
Published: April 2010

Abstract. In spite of the importance of Sudd (swamp) area estimation for any hydrological project in the southern Sudan, yet, no abroad agreement on its size, due to the inaccessibility and civil war. In this study, remote sensing techniques are used to estimate the Bahr El-Jebel flooded area. MODIS-Terra (Moderate Resolution Imaging Spectroradiometer) level 1B satellite images are analyzed on basis of the unsupervised classification method. The annual mean of Bahr El-Jebel flooded area has been estimated at 20 400 km2, which is 96% of Sutcliffe and Park (1999) estimation on basis of water balance model prediction. And only, 53% of SEBAL (Surface Energy Balance Algorithm for Land) model estimation. The accuracy of the classification is 71%. The study also found the swelling and shrinkage pattern of Sudd area throughout the year is following the trends of Lake Victoria outflow patterns. The study has used two evaporation methods (open water evaporation and SEBAL model) to estimate the annual storage volume of Bahr El-Jebel River by using a water balance model. Also the storage changes due time is generated throughout the study years.
Hydrological modelling for meso-scale catchments using globally available data
Authors: Gafurov A. , Götzinger J. , Bárdossy A.
Published: April 2010

Abstract. This study focuses on modelling water balances for catchments with limited data availability. The objective was to use globally available data for water balance modelling of meso-scale catchments. The study is carried out in two catchments; one having enough data for the performance check of the model and the other with very few data for model validation. Globally available meteorological and geographical data is used for the basic model inputs. Dissaggregation of the global data, both spatially and temporally, was conducted to distribute the available data across the watershed and to attain higher resolution input data for the model. In addition, a glacier module was developed for the regions covered by glaciers. The HBV-IWS model developed at the Institute of Hydraulic Engineering at the University of Stuttgart is applied. The outcomes of the modelling provide noteworthy results for both catchments that can be used in water resources planning and management issues. Moreover, the research presents the potential for modelling water balances using predominantly globally available data and proposes appropriate disaggregation methods for global data usage.
Uncertainties in rainfall retrievals from ground-based weather radar: overview, case study, and simulation experiment
Authors: Uijlenhoet R. , van der Wielen S. H. , Berne A.
Published: April 2010

Abstract. Because rainfall constitutes the main source of water for the terrestrial hydrological processes, accurate and reliable measurement and prediction of its spatial and temporal distribution over a wide range of scales is an important goal for hydrology. We investigate the potential of ground-based weather radar to provide such measurements through a detailed analysis of the associated observation uncertainties. First, a historical perspective on measuring the space-time distribution of rainfall, from the rain gauge to the radar era, is presented. Subsequently, we provide an overview of the various errors and uncertainties affecting radar rainfall retrievals. As an example, we present a case study of the relation between measurements from an operational C-band weather radar and a network of tipping bucket rain gauges as a function of range. Finally, a recently developed stochastic model of range profiles of rainfall microstructure is employed in a simulation experiment designed to investigate the rainfall retrieval uncertainties associated with weather radars operating in different widely used frequency bands.
Uncertainty in geological and hydrogeological data
Authors: Nilsson B. , Højberg A. L. , Refsgaard J. C. , Troldborg L.
Published: April 2010

Abstract. Uncertainty in conceptual model structure and in environmental data is of essential interest when dealing with uncertainty in water resources management. To make quantification of uncertainty possible it is necessary to identify and characterise the uncertainty in geological and hydrogeological data. This paper discusses a range of available techniques to describe the uncertainty related to geological model structure and scale of support. Literature examples on uncertainty in hydrogeological variables such as saturated hydraulic conductivity, specific yield, specific storage, effective porosity and dispersivity are given. Field data usually have a spatial and temporal scale of support that is different from the one on which numerical models for water resources management operate. Uncertainty in hydrogeological data variables is characterised and assessed within the methodological framework of the HarmoniRiB classification.
Effect of seasonal dynamics of vegetation cover on land surface models: a case study of NOAH LSM over a savanna farm land in eastern Burkina Faso, West Africa
Authors: Bagayoko F. , Yonkeu S. , van de Giesen N. C.
Published: April 2010

Abstract. The sensitivity of the land surface model of the National Centers for Environmental Prediction (NCEP), the Oregon State University, the Air Force and the Hydrologic Research Lab (NOAH LSM) was evaluated with respect to the seasonal dynamics of the vegetation cover in the savanna area under intensive agriculture in the eastern part of Burkina Faso, West Africa. The data collected during the first long-term measurement of the surface fluxes in this mentioned region was used for this purpose. The choice of NOAH LSM was motivated by the fact that it has already been tested in different environments in West Africa, especially in Ghana. The sensitivity was tested by comparing the simulated surfaces fluxes using a fixed values of the roughness length for momentum as a standard in the model and the true seasonal value of this variable. The results show that NOAH LSM was not sensitive to the change of the roughness length for momentum neither on a seasonal basis nor on a daily basis, which was found to be abnormal. The formulation of the coefficient (Bc) coupling the dry canopy transpiration to the atmosphere was found to be the main reason for this. An improved formulation for this coefficient was given to solve this insensitivity and to improve the performance of the model. Recommendations are also given to enhance the performance of the model in the West African savanna environment.
Defining the climatic signal in stream salinity trends using the Interdecadal Pacific Oscillation and its rate of change
Authors: McNeil V. H. , Cox M. E.
Published: April 2010

Abstract. The impact of landuse on stream salinity is difficult to separate from decadal climatic variability, as the decadal scale climatic cycles in ground water and stream hydrology have similar wavelengths to the landuse pattern. These hydrological cycles determine the stream salinity through accumulation or release of salt in the landscape. The Interdecadal Pacific Oscillation (IPO) has been investigated before as an indicator of hydrological and related time series in the southern hemisphere. This study presents a new approach, which uses the rate of change in the IPO, rather than just its absolute value, to define an indicator for the climate component of ambient shallow groundwater tables and corresponding stream salinity. Representative time series of water table and stream salinity indicators are compiled, using an extensive but irregular database covering a very wide geographical area. These are modelled with respect to the IPO and its rate of change to derive climatic indicators. The effect of removing the decadal climatic influence from stream salinity trends is demonstrated.
Threshold effects in catchment storm response and the occurrence and magnitude of flood events: implications for flood frequency
Authors: Kusumastuti D. I. , Struthers I. , Sivapalan M. , Reynolds D. A.
Published: April 2010

Abstract. The aim of this paper is to illustrate the effects of selected catchment storage thresholds upon runoff behaviour, and specifically their impact upon flood frequency. The analysis is carried out with the use of a stochastic rainfall model, incorporating rainfall variability at intra-event, inter-event and seasonal timescales, as well as infrequent summer tropical cyclones, coupled with deterministic rainfall-runoff models that incorporate runoff generation by both saturation excess and subsurface stormflow mechanisms. Changing runoff generation mechanisms (i.e. from subsurface flow to surface runoff) associated with a given threshold (i.e. saturation storage capacity) are shown to be manifested in the flood frequency curve as a break in slope. It is observed that the inclusion of infrequent summer storm events increases the temporal frequency occurrence and magnitude of surface runoff events, in this way contributing to steeper flood frequency curves, and an additional break in the slope of the flood frequency curve. The results of this study highlight the importance of thresholds on flood frequency, and provide insights into the complex interactions between rainfall variability and threshold nonlinearities in the rainfall-runoff process, which are shown to have a significant impact on the resulting flood frequency curves.
The Hydrologic Ensemble Prediction EXperiment (HEPEX)
Authors: Schaake J. , Franz K. , Bradley A. , Buizza R.
Published: April 2010

Abstract. Users of hydrologic predictions need reliable, quantitative forecast information, including estimates of uncertainty, for lead times ranging from less than an hour during flash flooding events to more than a year for long-term water management. To meet this need, operational agencies are developing hydrological ensemble forecast techniques to account for sources of uncertainty such as future precipitation, initial hydrological conditions, and hydrological model limitations including uncertain model parameters. Research advances in areas such as hydrologic modeling, data assimilation, ensemble prediction, and forecast verification need to be incorporated into operational forecasting systems to assure that the state-of-the-art products are reaching the forecast user community. The Hydrologic Ensemble Prediction EXperiment (HEPEX) has been formed to develop and demonstrate new hydrologic forecasting technologies, and to facilitate the implementation of beneficial technologies into the operational environment.
Sensitivity of point scale runoff predictions to rainfall resolution
Authors: Hearman A. J. , Hinz C.
Published: April 2010

Abstract. This paper investigates the effects of using non-linear, high resolution rainfall, compared to time averaged rainfall on the triggering of hydrologic thresholds and therefore model predictions of infiltration excess and saturation excess runoff. The bounded random cascade model, parameterized to south western Australian rainfall, was used to scale rainfall intensities at various time resolutions ranging from 1.875 min to 2 h. A one dimensional, conceptual rainfall partitioning model was used that instantaneously partitions water into infiltration excess, infiltration, storage, deep drainage, saturation excess and surface runoff, where the fluxes into and out of the soil store are controlled by thresholds. For example, saturation excess is triggered when the soil water content reaches the storage capacity threshold. The results of the numerical modelling were scaled by relating soil infiltration properties to soil draining properties, and inturn, relating these to average storm intensities. By relating maximum soil infiltration capacities to saturated drainage rates (f*), we were able to split soils into two groups; those where all runoff is a result of infiltration excess alone (f*≤0.2) and those susceptible to both infiltration excess and saturation excess runoff (f*>0.2). For all soil types, we related maximum infiltration capacities to average storm intensities (k*) and were able to show where model predictions of infiltration excess were most sensitive to rainfall resolution (ln k=0.4) and where using time averaged rainfall data can lead to an under prediction of infiltration excess and an over prediction of the amount of water entering the soil (ln k*>2). For soils susceptible to both infiltration excess and saturation excess, total runoff sensitivity was scaled by relating saturated drainage rates to average storm intensities (g*) and parameter ranges where predicted runoff was dominated by infiltration excess or saturation excess depending on the resolution of rainfall data was determined (ln g*<2). Infiltration excess predicted from high resolution rainfall is short and intense, whereas saturation excess produced from low resolution rainfall is more constant and less intense. This has important implications for the accuracy of current hydrological models that use time averaged rainfall under these soil and rainfall conditions and predictions of further thresholds such as erosion. It offers insight into areas where the understanding of the dynamics of high resolution rainfall is required and a means by which we can improve our understanding of the way variations in rainfall intensities within a storm relate to hydrological thresholds and model predictions.
Hydrological model coupling with ANNs
Authors: Kamp R. G. , Savenije H. H. G.
Published: April 2010

Abstract. Model coupling in general is necessary but complicated. Scientists develop and improve conceptual models to represent physical processes occurring in nature. The next step is to translate these concepts into a mathematical model and finally into a computer model. Problems may appear if the knowledge, encapsulated in a computer model and software program is needed for another purpose. In integrated water management this is often the case when connections between hydrological, hydraulic or ecological models are required. Coupling is difficult for many reasons, related to data formats, compatibility of scales, ability to modify source codes, etc. Hence, there is a need for an efficient and cost effective approach to model-coupling. One solution for model coupling is the use of Artificial Neural Networks (ANNs). The ANN can be used as a fast and effective model simulator which can connect different models. In this paper ANNs are used to couple four different models: a rainfall runoff model, a river channel routing model, an estuarine salt intrusion model, and an ecological model. The coupling as such has proven to be feasible and efficient. However the salt intrusion model appeared difficult to model accurately in an ANN. The ANN has difficulty to represent both short term (tidal) and long term (hydrological) processes.