bluuebunny/crossref_metadata_2025 huggingface dataset:
Importance of stream temperature to climate change impact on water quality
Authors: Ducharne A.
Published: April 2010

Abstract. The sensitivity of water quality to climate change was assessed in the Seine River (France) with the biogeochemical model RIVERSTRAHLER, which describes the transformations and fluxes of C, N, P and Si between the main microbiological populations, the water column and the sediment, along the entire river network. Point and diffuse sources are prescribed, stream temperature undergoes a sinusoidal annual cycle constrained by observations, and runoff is calculated by a physically-based land surface model. The reference simulation, using meteorological forcing of 1986–1990 and point sources of 1991, compares very well with observations. The climate change simulated by a general circulation model under the SRES emission scenario A2 was used to simulate the related changes in runoff and stream temperature. To this end, a statistical analysis was undertaken of the relationships between the water and air temperatures in the Seine watershed over 1993–1999, using 88 points that correctly sampled the variability of the tributaries. Most of stream temperature variance was explained by the lagged moving average of air temperature, with parameters that depended on Strahler stream order. As an interesting simplification, stream temperature changes could be approximated by air temperature changes. This modelling framework was used to analyse of the relative influence of the water warming and discharge reduction induced by climate change on water quality in Paris and downstream. Discharge reduction increased phytoplankton growth and oxygen deficits. Water warming decreased dissolved oxygen, increased phytoplankton biomass during the growth period, and reduced it afterwards, when loss factors dominate. It was also shown that these impacts were enhanced when point source inputs of nutrient and organic matter increased.
Dynamic analysis of groundwater discharge and partial-area contribution to Pukemanga Stream, New Zealand
Authors: Bidwell V. J. , Stenger R. , Barkle G. F.
Published: April 2010

Abstract. The proportion and origin of groundwater contribution to streamflow from agricultural catchments is relevant to estimation of the effects of nitrate leached from the soil on the quality of surface waters. This study addresses the partitioning of streamflow contributions from near-surface runoff and from groundwater, each with different contributing land area, on a steep pastoral hillslope in a humid climate. The 3 ha headwater catchment of the perennial Pukemanga Stream, in the North Island of New Zealand, was instrumented for continuous observation of climatic data, streamflow and groundwater level. The dynamics of groundwater levels and groundwater contribution to streamflow were analysed by means of a one-parameter, eigenvalue-eigenfunction description of a 1-D aquifer model. Model results for seven years of daily data predict that 36–44% of the topographical catchment contributes groundwater to the stream. The remaining groundwater generated within the catchment contributes to streamflow outside the catchment. After correction for contributing areas, groundwater was calculated to be 58–83% of observed annual catchment streamflow or 78–93% of flow generation on a unit area basis. Concurrent hourly data for streamflow and groundwater levels at two sites indicate the dynamic behaviour of a local groundwater system. Groundwater flow dynamics that support the perennial nature of this headwater stream are consistent with the size of the groundwater body, porosity of the subsurface material, and hydraulic conductivity derived from partitioning of streamflow contributions.
Prediction of littoral drift with artificial neural networks
Authors: Singh A. K. , Deo M. C. , Kumar V. S.
Published: April 2010

Abstract. The amount of sand moving parallel to a coastline forms a prerequisite for many harbour design projects. Such information is currently obtained through various empirical formulae. Despite much research in the past an accurate and reliable estimation of the rate of sand drift has still remained as a problem. The current study addresses this issue through the use of artificial neural networks (ANN). Feed forward networks were developed to predict the sand drift from a variety of causative variables. The best network was selected after trying out many alternatives. In order to improve the accuracy further its outcome was used to develop another network. Such simple two-stage training yielded most satisfactory results. An equation combining the network and a non-linear regression is presented for quick field usage. An attempt was made to see how both ANN and statistical regression differ in processing the input information. The network was validated by confirming its consistency with the underlying physical process.
Projeto Vida no Vale: universal access to water and sanitation in the North East of Minas Gerais (Brazil)
Authors: Kauark-Leite L. , Vinçon-Leite B. , Deroubaix J. F. , Loireau A. , Silveira D. , Haddad E.
Published: April 2010

Abstract. In the rural areas of the developing countries, the access to water supply and sanitation services is still largely inadequate. Poor governance of the water sector is frequently singled out as a cause and reforms are required. Studies analyzing the great diversity of restructuring efforts currently being undertaken in the water sector have not succeeded in determining the most appropriate institutional and economic framework for such reforms. Moreover they underline the lack of documentation on actual projects and call for concrete models and tools for improving water and sanitation services (WSS) and for adapting water utility practice to real conditions. In this context, the Vida no Vale (Life in the Valley) project is aimed at bringing universal access to WSS for all inhabitants of both urban and rural areas, in the north-eastern area of the Brazilian State of Minas Gerais. The project takes sustainable development as its guiding principle, and relies on the joint implementation of an innovative technical design, a governance model involving public participation and subsidiarity, and an economic structure combining financial viability and social equity. Designed at a consistent geographical and hydrological scale, it includes the creation of a regional subsidiary of the existing state water company as a keystone element. The institutional organisation also relies on the creation of a public board consisting of the 92 municipalities of the project region and of the State of Minas Gerais. This board will be in charge of the system's governance. The paper will present the first step of the project (2006), consisting of a feasibility study and the implementation of 9 pilot sub-projects. During the feasibility study, the supply, demand and capacity to pay for water services were defined, existing infrastructure appraised, the necessary amount of investment assessed and an innovative operational model and a sustainable management system, including civil society participation, defined. The main features of the Vida no Vale project have been tested in 9 pilot sub-projects, and implemented in municipalities chosen for their low Human Development Index and for the lack of WSS, in both urban and rural areas. A second phase corresponding to the project's final implementation will run from 2007 to 2011. The ongoing successful accomplishment of the Vida no Vale project would make it an exemplary and replicable model for other poor regions.
Seasonality in the alpine water logistic system on a regional basis
Authors: Vanham D. , Fleischhacker E. , Rauch W.
Published: April 2010

Abstract. In this study the water logistic system is defined as the interaction of the subsystems water resources, water supply and water demand in terms of water flow. The analysis of a water balance in alpine regions is strongly influenced by both temporal and spatial seasonal fluctuations within these elements, the latter due to the vertical dimension of mountainous areas. Therefore the determination of different seasons plays a key role within the assessment of alpine water logistic systems. In most studies a water balance for a certain region is generated on an annual, monthly or classic 4-seasonal basis. This paper presents a GIS-based multi criteria method to determine an optimal winter and summer period, taking into account different water demand stakeholders, alpine hydrology and the characteristic present day water supply infrastructure of the Alps. Technical snow-making and (winter) tourism were identified as the two major seasonal water demand stakeholders in the study area, which is the Kitzbueheler region in the Austrian Alps. Based upon the geographical datasets mean snow cover start and end date, winter was defined as the period from December to March, and summer as the period from April to November.
Climate change impact assessment as function of model inaccuracy
Authors: Droogers P. , van Loon A. , Immerzeel W.
Published: April 2010

Abstract. Numerical simulation models are frequently applied to assess the impact of climate change on hydrology and agriculture. A common hypothesis is that unavoidable model errors are reflected in the reference situation as well as in the climate change situation so that by comparing reference to scenario model errors will level out. For a polder in The Netherlands an innovative procedure has been introduced, referred to as the Model-Scenario-Ratio (MSR), to express model inaccuracy on climate change impact assessment. MSR values close to 1, indicating that impact assessment is mainly a function of the scenario itself rather than of the quality of the model, were found for most indicators evaluated. More extreme climate change scenarios and indicators based on threshold values showed lower MSR values, indicating that model accuracy is an important component of the climate change impact assessment. It was concluded that the MSR approach can be applied easily and will lead to more robust impact assessment analyses.
Winter climate affects long-term trends in stream water nitrate in acid-sensitive catchments in southern Norway
Authors: de Wit H. A. , Hindar A. , Hole L.
Published: April 2010

Abstract. Controls of stream water NO3 in mountainous and forested catchments are not thoroughly understood. Long-term trends in stream water NO3 are positive, neutral and negative, often apparently independent of trends in N deposition. Here, time series of NO3 in four small acid-sensitive catchments in southern Norway were analysed in order to identify likely drivers of long-term changes in NO3. In two sites, stream water NO3 export declined ca 50% over a period of 25 years while in the other sites NO3 export increased with roughly 20%. Discharge and N deposition alone were poor predictors of these trends. The most distinct trends in NO3 were found in winter and spring. Empirical models explained between 45% and 61% of the variation in weekly concentrations of NO3, and described both upward and downward seasonal trends tolerably well. Key explaining variables were snow depth, discharge, temperature and N deposition. All catchments showed reductions in snow depth and increases in winter discharge. In two inland catchments, located in moderate N deposition areas, these climatic changes appeared to drive the distinct decreases in winter and spring concentrations and fluxes of NO3. In a coast-near mountainous catchment in a low N deposition area, these climatic changes appeared to have the opposite effect, i.e. lead to increases in especially winter NO3. This suggests that the effect of a reduced snow pack may result in both decreased and increased catchment N leaching depending on interactions with N deposition, soil temperature regime and winter discharge.
Influence of summer and winter climate variability on nitrogen wet deposition in Norway
Authors: Hole L. R. , de Wit H. A. , Aas W.
Published: April 2010

Abstract. Dominating wind patterns around Norway may change due to climate warming. This could affect transport of polluted air masses and precipitation. Here, we study relations between reactive nitrogen wet deposition and air mass transport during summer and winter expressed in the form of climate indices, at seven sites in Southern Norway for the period 1980–2005. Atmospheric nitrate concentrations decreased with 0 to 50% in the period, particularly at sites with little precipitation, and mostly during 1990–2005. For comparison, reported reductions in emissions of oxidised nitrogen in Europe in 1989–2003 were 23%. Climate indices explained up to 36% of the variation in winter nitrate deposition at the western and northern sites – and also explained 60% of the variation in winter precipitation (R=0.77). This suggests that the variation in nitrate wet deposition is closely related to variation in precipitation, and that the climate indices seem to also partly control the variation in atmospheric nitrate concentrations (R=−0.45 at coastal sites). At the coastal sites, local air temperature was highly correlated (R=0.84) with winter nitrate deposition, suggesting that warm, humid winter weather results in increased wet nitrate deposition. For ammonia the pattern was similar, but this compound is more influenced by local sources. Expected severe increase in precipitation in western and northern regions as a consequence of climate change suggest that nitrogen deposition in these areas will increase under global warming if emissions are held constant.
What affects the nitrogen retention in Tatra Mountains lakes' catchments in Poland?
Authors: Rzychoń D. , Worsztynowicz A.
Published: April 2010

Abstract. The study of acidification and recovery of two lakes situated in the Polish Tatra Mountains, exposed to similar deposition of acidic substances but differing in altitude, catchment morphology, hydrology, and biodiversity is presented. Measurements were performed in 1992–1996 and 2001–2005. Simultaneously, research on the atmospheric deposition was carried out. The following physical and chemical parameters in lake water and precipitation were measured: pH, conductivity (K25), Ca2+, Mg2+, Na+, K+, NH4+, SO42−, NO3−, Cl− and alkalinity. Distinct changes in the chemical composition of precipitation were observed over 14 years (1992–2005). During this time the sulphate concentration decreased significantly, and the concentration of hydrogen ions in precipitation decreased at an average rate of 2.23 meq/m³/yr. There was no significant change in nitrate, ammonium or total nitrogen deposition. The chemical composition of water of both lakes changed significantly and showed signs of chemical recovery with decreases in sulphate concentration and increases in acid neutralising capacity. The concentration of base cations declined. Despite the lack of clear trends in nitrogen deposition, a statistically significant drop in concentration was observed in the two lakes. A significant increase of about 15% in the retention of nitrogen compounds in both catchments occurred. An improvement in nitrogen saturation status in both catchments was observed. This probably resulted mainly from decreasing acidification and global warming which prolongs the vegetative period, changes plant species composition and increases the microbiological activity of soil.
Modelling the effects of climate on long-term patterns of dissolved organic carbon concentrations in the surface waters of a boreal catchment
Authors: Futter M. N. , Starr M. , Forsius M. , Holmberg M.
Published: April 2010

Abstract. Dissolved organic carbon concentrations ([DOC]) in surface waters are increasing in many regions of Europe and North America. These increases are likely driven by a combination of changing climate, recovery from acidification and change in severity of winter storms in coastal areas. INCA-C, a process-based model of climate effects on surface water [DOC], was used to explore the mechanisms by which changing climate controls seasonal to inter-annual patterns of [DOC] in the lake and outflow stream of a small Finnish catchment between 1990 and 2003. Both production in the catchment and mineralization in the lake controlled [DOC] in the lake. Concentrations in the catchment outflow were controlled by rates of DOC production in the surrounding organic soils. The INCA-C simulation results were compared to those obtained using artificial neural networks (ANN). In general, "black box" ANN models provide better fits to observed data but process-based models can identify the mechanism responsible for the observed pattern. A statistically significant increase was observed in both INCA-C modelled and measured annual average [DOC] in the lake. This suggests that some of the observed increase in surface water [DOC] is caused by climate-related processes operating in the lake and catchment. However, a full understanding of surface water [DOC] dynamics can only come from catchment-scale process-based models linking the effects of changing climate and deposition on aquatic and terrestrial environments.
Structured hydrological analysis for targeting fallow evaporation to improve water productivity at the irrigation system level
Authors: Khan S. , Hafeez M. M. , Rana T. , Mushtaq S.
Published: April 2010

Abstract. This paper provides results of an application of a holistic systematic approach of water accounting using remote sensing and GIS coupled with ground water modeling to evaluate water saving options by tracking non-beneficial evaporation in the Liuyuankou Irrigation System (LIS) of China. Groundwater rise is a major issue in the LIS, where groundwater levels have risen alarmingly close to the ground surface (within 1 m) near the Yellow River. The lumped water balance analysis showed high fallow evaporation losses and which need to be reduced for improving water productivity. The seasonal actual evapotranspiration (ETs) was estimated by applying the SEBAL algorithm for eighteen NOAA AVHRR-12 images over the year of 1990–1991. This analysis was aided by the unsupervised land use classification applied to two Landsat 5 TM images of the study area. SEBAL results confirmed that a significant amount (116.7 MCM) of water can be saved by reducing ETs from fallow land which will result in improved water productivity at the irrigation system. The water accounting indicator (for the analysis period) shows that the process fraction per unit of depleted water (PFdepleted) is 0.52 for LIS, meaning that 52% of the depleted water is consumed by agricultural crops and 48% is lost through non-process depletion. Finally, the groundwater modeling was applied to simulate three land use and water management interventions to assess their effectiveness for both water savings and impact on the groundwater in LIS. MODFLOW's Zone Budget code calculates the groundwater budget of user-specified subregions, the exchange of flows between subregions and also calculates a volumetric water budget for the entire model at the end of each time step. The simulation results showed that fallow evaporation could be reduced between 14.2% (25.51 MCM) and 45.3% (81.36 MCM) by interventions such as canal lining and ground water pumping. The reduction in non-beneficial ETs volumes would mean that more water would be available for other uses and it would allow the introduction of more surface water supplies in the area through improved water management strategies. This will ultimately lead to improved water productivity of the LIS system.
Predicting long-term recovery of a strongly acidified stream using MAGIC and climate models (Litavka, Czech Republic)
Authors: Hardekopf D. W. , Horecký J. , Kopáček J. , Stuchlík E.
Published: April 2010

Abstract. Two branches forming the headwaters of a stream in the Czech Republic were studied. Both streams have similar catchment characteristics and historical deposition; however one is rain-fed and strongly affected by acid atmospheric deposition, the other spring-fed and only moderately acidified. The MAGIC model was used to reconstruct past stream water and soil chemistry of the rain-fed branch, and predict future recovery up to 2050 under current proposed emissions levels. A future increase in air temperature calculated by a regional climate model was then used to derive climate-related scenarios to test possible factors affecting chemical recovery up to 2100. Macroinvertebrates were sampled from both branches, and differences in stream chemistry were reflected in the community structures. According to modelled forecasts, recovery of the rain-fed branch will be gradual and limited, and continued high levels of sulphate release from the soils will continue to dominate stream water chemistry, while scenarios related to a predicted increase temperature will have little impact. The likelihood of colonization of species from the spring-fed branch was evaluated considering the predicted extent of chemical recovery. The results suggest that the possibility of colonization of species from the spring-fed branch to the rain-fed will be limited to only the acid-tolerant stonefly, caddisfly and dipteran taxa in the modelled period.
Utility of daily vs. monthly large-scale climate data: an intercomparison of two statistical downscaling methods
Authors: Maurer E. P. , Hidalgo H. G.
Published: April 2010

Abstract. Downscaling of climate model data is essential to most impact analysis. We compare two methods of statistical downscaling to produce continuous, gridded time series of precipitation and surface air temperature at a 1/8-degree (approximately 140 km² per grid cell) resolution over the western U.S. We use NCEP/NCAR Reanalysis data from 1950–1999 as a surrogate General Circulation Model (GCM). The two methods included are constructed analogues (CA) and a bias correction and spatial downscaling (BCSD), both of which have been shown to be skillful in different settings, and BCSD has been used extensively in hydrologic impact analysis. Both methods use the coarse scale Reanalysis fields of precipitation and temperature as predictors of the corresponding fine scale fields. CA downscales daily large-scale data directly and BCSD downscales monthly data, with a random resampling technique to generate daily values. The methods produce comparable skill in producing downscaled, gridded fields of precipitation and temperatures at a monthly and seasonal level. For daily precipitation, both methods exhibit some skill in reproducing both observed wet and dry extremes and the difference between the methods is not significant, reflecting the general low skill in daily precipitation variability in the reanalysis data. For low temperature extremes, the CA method produces greater downscaling skill than BCSD for fall and winter seasons. For high temperature extremes, CA demonstrates higher skill than BCSD in summer. We find that the choice of most appropriate downscaling technique depends on the variables, seasons, and regions of interest, on the availability of daily data, and whether the day to day correspondence of weather from the GCM needs to be reproduced for some applications. The ability to produce skillful downscaled daily data depends primarily on the ability of the climate model to show daily skill.
Sustainable water services and interaction with water resources in Europe and in Brazil
Authors: Barraqué B. , Formiga Johnsson R. M. , Britto A. L.
Published: April 2010

Abstract. The increasing interaction between large cities and nature makes "urban water" an issue: water resources and water services – including public water supply, sewage collection and treatment, and in large cities, storm water control –, which had become separate issues thanks to the process of water transport and treatment technologies, are now increasingly interfering with each other. We cannot take nature for granted anymore, and we need to protect water resources, if only to reduce the long term cost of transporting and treating water. In this paper, we compare the historical development of water industry technologies in European and Brazilian metropolitan areas, in their socio-economic and political context, tracing it through three "ages" of water technology and services which developed under civil engineering, sanitary engineering, and environmental engineering perspectives: the "quantity of water" and civil engineering paradigm was developed on the assumption that water should be drawn from natural environments far from the cities; in the "water quality" and chemical/sanitation engineering paradigm, water treatment was invented and allowed cities to take water from rivers closer to them and treat it, but also to reduce sewer discharge impacts; finally, the environmental engineering paradigm proposes to overcome the supply side perspective, by introducing demand side management, water conservation, water allocation flexibilisation, and an integrated approach to water services, water resources management, and land use policies.
Spatial disaggregation of bias-corrected GCM precipitation for improved hydrologic simulation: Ping River Basin, Thailand
Authors: Sharma D. , Das Gupta A. , Babel M. S.
Published: April 2010

Abstract. Global Climate Models (GCMs) precipitation scenarios are often characterized by biases and coarse resolution that limit their direct application for basin level hydrological modeling. Bias-correction and spatial disaggregation methods are employed to improve the quality of ECHAM4/OPYC SRES A2 and B2 precipitation for the Ping River Basin in Thailand. Bias-correction method, based on gamma-gamma transformation, is applied to improve the frequency and amount of raw GCM precipitation at the grid nodes. Spatial disaggregation model parameters (β,σ2), based on multiplicative random cascade theory, are estimated using Mandelbrot-Kahane-Peyriere (MKP) function at q=1 for each month. Bias-correction method exhibits ability of reducing biases from the frequency and amount when compared with the computed frequency and amount at grid nodes based on spatially interpolated observed rainfall data. Spatial disaggregation model satisfactorily reproduces the observed trend and variation of average rainfall amount except during heavy rainfall events with certain degree of spatial and temporal variations. Finally, the hydrologic model, HEC-HMS, is applied to simulate the observed runoff for upper Ping River Basin based on the modified GCM precipitation scenarios and the raw GCM precipitation. Precipitation scenario developed with bias-correction and disaggregation provides an improved reproduction of basin level runoff observations.
Extension of the Representative Elementary Watershed approach for cold regions: constitutive relationships and an application
Authors: Mou L. , Tian F. , Hu H. , Sivapalan M.
Published: April 2010

Abstract. The representative elementary watershed (REW) approach proposed by Reggiani et al. (1998, 1999) represents an attempt to develop a scale adaptable modeling framework for the hydrological research community. Tian et al. (2006a) extended the original REW theory for cold regions through explicit treatment of energy balance equations to incorporate associated cold regions processes, such as melting and accumulation of glacier and snow, and freezing and thawing of soil ice. However, constitutive relationships for the cold regions processes needed to complete these new balance equations have been left unspecified in this derivation. In this paper we propose a set of closure scheme for cold regions processes within the extended framework provided by Tian et al. (2006a). A rigorous energy balance method is proposed to close the balance equations of melting/accumulation processes as well as the widely-used and conceptual degree-day method, whereas the closure schemes for soil freezing and thawing are based on the "maximum unfrozen-water content" model. The proposed closure schemes are coupled to the previously derived balance equations and implemented within Thermodynamic Watershed Hydrological Model (THModel, Tian, 2006b) and then applied to the headwaters of the Urumqi River in Western China. The results of the 4-year calibration and 1-year validation analyses show that THModel can indeed simulate runoff processes in this snow and glacier-dominated catchment very well, which confirms the applicability of the modeling based on the REW approach and the validity of the developed closure schemes for cold regions processes.
Sensitivity analysis and parameter estimation for the distributed modeling of infiltration excess overland flow
Authors: Castaings W. , Dartus D. , Le Dimet F.-X. , Saulnier G.-M.
Published: April 2010

Abstract. The variational methods widely used for other environmental systems are applied to a spatially distributed flash flood model coupling kinematic wave overland flow and Green Ampt infiltration. Using an idealized configuration where only parametric uncertainty is addressed, the potential of this approach is illustrated for sensitivity analysis and parameter estimation. Adjoint sensitivity analysis provides an extensive insight into the relation between model parameters and the hydrological response and enables the use of efficient gradient based optimization techniques.
Modelling groundwater-dependent vegetation patterns using ensemble learning
Authors: Peters J. , De Baets B. , Samson R. , Verhoest N. E. C.
Published: April 2010

Abstract. Vegetation patterns arise from the interplay between intraspecific and interspecific biotic interactions and from different abiotic constraints and interacting driving forces and distributions. In this study, we constructed an ensemble learning model that, based on spatially distributed environmental variables, could model vegetation patterns at the local scale. The study site was an alluvial floodplain with marked hydrologic gradients on which different vegetation types developed. The model was evaluated on accuracy, and could be concluded to perform well. However, model accuracy was remarkably lower for boundary areas between two distinct vegetation types. Subsequent application of the model on a spatially independent data set showed a poor performance that could be linked with the niche concept to conclude that an empirical distribution model, which has been constructed on local observations, is incapable to be applied beyond these boundaries.
The co-production of a "relevant" expertise – administrative and scientific cooperation in the French water policies elaboration and implementation
Authors: Deroubaix J. F.
Published: April 2010

Abstract. This paper aims at understanding the social and political uses of the principle of integrated management and its possible impacts on the elaboration and implementation processes of public policies in the French water management field. The academic and political innovations developed by scientists and agents of the administration these last 25 years are analysed, using some of the theoretical tools developed by the science studies and public policy analysis. We first focus on the construction of intellectual public policy communities such as the GIP Hydro systems, at the origin of large interdisciplinary research programs in the 1990s. A common cognitive framework is clearly built during this period on the good governance of the aquatic ecosystems and on the corresponding needs and practices of research. The second part of the paper focuses on the possibilities to build political communities and more or less integrated expertises in the decision making processes concerning various issues related to water management. Eutrophication and its inscription on the French political agenda is a very significant case for analysing the difficulty to build such a political community. On the contrary, when there is an opportunity for policy evaluation, which was the case concerning the management of wetlands in France or the implementation of compulsory flows on the French rivers, these communities can emerge. However, the type of integrated expertise and management proposed in these cases of policy evaluations much depends on their methodological choices.
Establishment of a catchment monitoring network through a participatory approach in a small rural catchment in South Africa
Authors: Kongo V. M. , Kosgei J. R. , Jewitt G. P. W. , Lorentz S. A.
Published: April 2010

Abstract. The establishment of a catchment monitoring network is a process, from the inception of the idea to its implementation, the latter being the construction of relevant gauging structures and installation of the various instruments. It is useful that the local communities and other stakeholders are involved and participate in such a process as was realised during the establishment of the hydrological monitoring network in the Potshini catchment in the Bergville district in the KwaZulu-Natal Province in South Africa. The paper illustrates the participatory application of various methods and techniques for establishing a hydrological monitoring network, in a small rural inhabited catchment, to monitor hydrological processes at both field and catchment scale for research purposes in water resources management. The authors conclude that the participation of the local community and other stakeholders in catchment monitoring and instilling the sense of ownership and management of natural resources to the local communities needs to be encouraged at all times. Success stories in water resources management by local communities can be realized if such a process is integrated with other development plans in the catchment at all forums with due recognition of the social dynamics of the communities living in the catchment.
Analysis of soil and vegetation patterns in semi-arid Mediterranean landscapes by way of a conceptual water balance model
Authors: Portoghese I. , Iacobellis V. , Sivapalan M.
Published: April 2010

Abstract. This paper investigates the impact of various vegetation types on water balance variability in semi-arid Mediterranean landscapes, and the different strategies they may have developed to succeed in such water-limited environments. Water balance constraints are assumed to dominate the organization of landscapes and a conceptual bucket approach is adopted to model the temporal water balance dynamics, with vegetation water use efficiency being parameterized through the use of empirically obtained crop coefficients as surrogates of vegetation behavior in various developmental stages. Sensitivity analyses with respect to the root zone depth and soil water holding capacity are carried out with the aim of investigating the existence of preferential soil-vegetation associations and, hence, the spatial distribution of vegetation types within the study region. Based on these sensitivity analyses the degrees of suitability and adaptability of each vegetation type to parts of the study region are explored with respect of the soil water holding capacity, and the model results were found to be able to explain the observed affinity patterns. Finally, the existence of such preferential association between soil water holding capacity and vegetation species is verified through an extensive soil survey available in the study region.
Towards model evaluation and identification using Self-Organizing Maps
Authors: Herbst M. , Casper M. C.
Published: April 2010

Abstract. The reduction of information contained in model time series through the use of aggregating statistical measures is very high compared to the amount of information that one would like to draw from it for model identification and calibration purposes. Applied within a model identification context, aggregating statistical performance measures are inadequate to capture details on time series characteristics. It has been readily shown that this loss of information on the residuals imposes important limitations on model identification and -diagnostics and thus constitutes an element of the overall model uncertainty. In this contribution we present an approach using a Self-Organizing Map (SOM) to circumvent the identifiability problem induced by the low discriminatory power of aggregating performance measures. Instead, a Self-Organizing Map is used to differentiate the spectrum of model realizations, obtained from Monte-Carlo simulations with a distributed conceptual watershed model, based on the recognition of different patterns in time series. Further, the SOM is used instead of a classical optimization algorithm to identify the model realizations among the Monte-Carlo simulations that most closely approximate the pattern of the measured discharge time series. The results are analyzed and compared with the manually calibrated model as well as with the results of the Shuffled Complex Evolution algorithm (SCE-UA).
Assessing the biodegradability of terrestrially-derived organic matter in Scottish sea loch sediments
Authors: Loh P. S. , Miller A. E. J. , Reeves A. D. , Harvey S. M. , Overnell J.
Published: April 2010

Abstract. Lignin oxidation products were used to determine the sources, transport and distribution of terrestrially-derived organic matter (OM) in two Scottish sea lochs, Loch Creran and Loch Etive. Oxygen uptake rates, molar OC/N ratios (from bulk elemental analysis) and Rp values (from loss on ignition experiments, the ratio of the refractory to total OM) were also determined for sediments along transects of the lochs. Lignin data indicate the importance of riverine inputs, contributing land-derived carbon to the lochs as total lignin (Λ, mg/100 mg organic carbon, OC) decreased from 0.69 to 0.45 and 0.70 to 0.29 from the head to outside of Lochs Creran and Etive, respectively. In addition, significant correlations for lignin content against total OM and OC (p<0.05) also suggest a distinct contribution of terrestrial OM to carbon pools in the lochs. The general trend of decreasing oxygen uptake rates from the head (20.8 mmole m−2 day−1) to mouth (9.4 mmole m−2 day−1) of Loch Creran indicates decomposition of some terrestrial OM. Biodegradability of the sediment OM was also characterized by the increase of Rp values from the head to mouth of the lochs: 0.40 to 0.80 for Etive and 0.43 to 0.63 in Creran. Further, the molar OC/N ratio decreased from 11.2 to 6.4 in Creran, and from 17.5 to 8.2 in Etive. Our results show that the relatively fresh, terrestrially-derived OM, which is still susceptible to mineralization, plays an important role in fuelling the biogeochemical cycling of carbon in both systems. This work also demonstrates that oxygen uptake rate, Rp value and molar OC/N ratio are able to serve as useful proxies to indicate sediment biodegradability.
Global-scale modeling of groundwater recharge
Authors: Döll P. , Fiedler K.
Published: April 2010

Abstract. Long-term average groundwater recharge, which is equivalent to renewable groundwater resources, is the major limiting factor for the sustainable use of groundwater. Compared to surface water resources, groundwater resources are more protected from pollution, and their use is less restricted by seasonal and inter-annual flow variations. To support water management in a globalized world, it is necessary to estimate groundwater recharge at the global scale. Here, we present a best estimate of global-scale long-term average diffuse groundwater recharge (i.e. renewable groundwater resources) that has been calculated by the most recent version of the WaterGAP Global Hydrology Model WGHM (spatial resolution of 0.5° by 0.5°, daily time steps). The estimate was obtained using two state-of-the art global data sets of gridded observed precipitation that we corrected for measurement errors, which also allowed to quantify the uncertainty due to these equally uncertain data sets. The standard WGHM groundwater recharge algorithm was modified for semi-arid and arid regions, based on independent estimates of diffuse groundwater recharge, which lead to an unbiased estimation of groundwater recharge in these regions. WGHM was tuned against observed long-term average river discharge at 1235 gauging stations by adjusting, individually for each basin, the partitioning of precipitation into evapotranspiration and total runoff. We estimate that global groundwater recharge was 12 666 km3/yr for the climate normal 1961–1990, i.e. 32% of total renewable water resources. In semi-arid and arid regions, mountainous regions, permafrost regions and in the Asian Monsoon region, groundwater recharge accounts for a lower fraction of total runoff, which makes these regions particularly vulnerable to seasonal and inter-annual precipitation variability and water pollution. Average per-capita renewable groundwater resources of countries vary between 8 m3/(capita yr) for Egypt to more than 1 million m3/(capita yr) for the Falkland Islands, the global average in the year 2000 being 2091 m3/(capita yr). Regarding the uncertainty of estimated groundwater resources due to the two precipitation data sets, deviation from the mean is less than 1% for 50 out of the 165 countries considered, between 1 and 5% for 62, between 5 and 20% for 43 and between 20 and 80% for 10 countries. Deviations at the grid scale can be much larger, ranging between 0 and 186 mm/yr.
Value of river discharge data for global-scale hydrological modeling
Authors: Hunger M. , Döll P.
Published: April 2010

Abstract. This paper investigates the value of observed river discharge data for global-scale hydrological modeling of a number of flow characteristics that are required for assessing water resources, flood risk and habitat alteration of aqueous ecosystems. An improved version of WGHM (WaterGAP Global Hydrology Model) was tuned in a way that simulated and observed long-term average river discharges at each station become equal, using either the 724-station dataset (V1) against which former model versions were tuned or a new dataset (V2) of 1235 stations and often longer time series. WGHM is tuned by adjusting one model parameter (γ) that affects runoff generation from land areas, and, where necessary, by applying one or two correction factors, which correct the total runoff in a sub-basin (areal correction factor) or the discharge at the station (station correction factor). The study results are as follows. (1) Comparing V2 to V1, the global land area covered by tuning basins increases by 5%, while the area where the model can be tuned by only adjusting γ increases by 8% (546 vs. 384 stations). However, the area where a station correction factor (and not only an areal correction factor) has to be applied more than doubles (389 vs. 93 basins), which is a strong drawback as use of a station correction factor makes discharge discontinuous at the gauge and inconsistent with runoff in the basin. (2) The value of additional discharge information for representing the spatial distribution of long-term average discharge (and thus renewable water resources) with WGHM is high, particularly for river basins outside of the V1 tuning area and for basins where the average sub-basin area has decreased by at least 50% in V2 as compared to V1. For these basins, simulated long-term average discharge would differ from the observed one by a factor of, on average, 1.8 and 1.3, respectively, if the additional discharge information were not used for tuning. The value tends to be higher in semi-arid and snow-dominated regions where hydrological models are less reliable than in humid areas. The deviation of the other simulated flow characteristics (e.g. low flow, inter-annual variability and seasonality) from the observed values also decreases significantly, but this is mainly due to the better representation of average discharge but not of variability. (3) The optimal sub-basin size for tuning depends on the modeling purpose. On the one hand, small basins between 9000 and 20 000 km2 show a much stronger improvement in model performance due to tuning than the larger basins, which is related to the lower model performance (with and without tuning), with basins over 60 000 km2 performing best. On the other hand, tuning of small basins decreases model consistency, as almost half of them require a station correction factor.
Forecasting land-use change and its impact on the groundwater system of the Kleine Nete catchment, Belgium
Authors: Dams J. , Woldeamlak S. T. , Batelaan O.
Published: April 2010

Abstract. Land-use change and climate change, along with groundwater pumping are frequently indicated to be the main human-induced factors influencing the groundwater system. Up till now, research has mainly been focusing on the effect of the water quality of these human-induced changes on the groundwater system, often neglecting changes in quantity. The focus in this study is on the impact of land-use changes in the near future, from 2000 until 2020, on the groundwater quantity and the general hydrologic balance of a sub-catchment of the Kleine Nete, Belgium. This study tests a new methodology which involves coupling a land-use change model with a water balance model and a groundwater model. The future land-use is modelled with the CLUE-S model. Four scenarios (A1, A2, B1 and B2) based on the Special Report on Emission Scenarios (SRES) are used for the land-use modelling. Water balance components, groundwater level and baseflow are simulated using the WetSpass model in conjunction with a MODFLOW groundwater model. Results show that the average recharge slowly decreases for all scenarios, the decreases are 2.9, 1.6, 1.8 and 0.8% for respectively scenario A1, A2, B1 and B2. The predicted reduction in recharge results in a small decrease of the average groundwater level, ranging from 2.5 cm for scenario A1 to 0.9 cm for scenario B2, and a reduction of the total baseflow with maximum 2.3% and minimum 0.7% respectively for scenario A1 and B2. Although these average values do not indicate significant changes for the groundwater system, spatial analysis of the changes shows the changes are concentrated in the neighbourhood of the major cities in the study areas. It is therefore important for spatial managers to take the groundwater system into account for reducing the negative impacts of land-use and climate change as much as possible.
Comparing model performance of two rainfall-runoff models in the Rhine basin using different atmospheric forcing data sets
Authors: te Linde A. H. , Aerts J. C. J. H. , Hurkmans R. T. W. L. , Eberle M.
Published: April 2010

Abstract. Due to the growing wish and necessity to simulate the possible effects of climate change on the discharge regime on large rivers such as the Rhine in Europe, there is a need for well performing hydrological models that can be applied in climate change scenario studies. There exists large variety in available models and there is an ongoing debate in research on rainfall-runoff modelling on whether or not physically based distributed models better represent observed discharges than conceptual lumped model approaches do. In this paper, the hydrological models HBV and VIC were compared for the Rhine basin by testing their performance in simulating discharge. Overall, the semi-distributed conceptual HBV model performed much better than the distributed physically based VIC model (E=0.62, r2=0.65 vs. E=0.31, r2=0.54 at Lobith). It is argued here that even for a well-documented river basin such as the Rhine, more complex modelling does not automatically lead to better results. Moreover, it is concluded that meteorological forcing data has a considerable influence on model performance, irrespectively to the type of model structure and the need for ground-based meteorological measurements is emphasized.