Showing papers in "IAHS-AISH publication in 2006"

A bounded version of the Nash-Sutcliffe criterion for better model assessment on large sets of basins

Abstract: Rainfall-runoff models are useful tools for hydrological research, water engineering and environmental applications Given the large number of available rainfall-runoff models, many comparative studies have been done to compare models performances, to specify their domain of application and provide guidance to end-users Although most existing comparative studies tested models only on a few basins, we believe that effective model evaluation requires large samples of test catchments However, large test samples raise the issue of appropriate criteria to quantify model performances This paper shows that the widely used Nash and Sutcliffe criterion may be difficult to apply for large test samples and that a bounded version of this criterion (called C 2M ) is better suited for extensive model assessment

Issues in flood forecasting: ungauged basins, extreme floods and uncertainty

Abstract: La prevision des crues pour n'importe quel site en contexte incertain pendant les periodes de precipitations intenses comprend trois aspects qui recouvrent d'importants defis scientifiques et la perspective d'une amelioration de l'annonce de crue La prevision pour des bassins non jauges utilisant une regionalisation empirique des parametres de modeles simplifies a obtenu des succes mitiges et fourni quelques progres a notre comprehension de la science hydrologique Des prototypes de modeles spatialises a base physico-conceptuelle, s'appuyant sur des donnees des terrains et des sols, sont ici mis a l'epreuve et montrent leurs avantages pour les bassins de plaine a reponse complexe Sur la base d'une d'etude de cas d'averses historiques extremes et de leur amplification, on peut demontrer le potentiel des modeles pluie-debit distribues pour l'annonce de crue et l'identification des emplacements sujets a inondation, particulierement en ce qui concerne les averses inhabituelles ou extremes et les sites non jauges Les problemes de l'initialisation du modele, de la mise a jour des previsions et de l'estimation des incertitudes sont discutes en relation avec la nature de ces modeles spatialises, les avancees attendues de la prevision des precipitations et les benefices de l'aide a la decision fondee sur l'analyse de risque appliquee a l'annonce de crue

The US MOPEX data set.

Abstract: A key step in applying land surface parameterization schemes is to estimate model parameters that vary spatially and are unique to each computational element Improved methods for parameter estimation (especially for parameters important to runoff response) are needed and require data from a wide range of climate regimes throughout the world Accordingly, the GEWEX Hydrometeorology Panel (GHP) endorsed the concept of an international Model Parameter Estimation Project (MOPEX) at its Toronto meeting, August 1996 Phase I of MOPEX was funded by NOAA in financial year (FY) 1997, Phase II in FY 2000 and Phase III in FY 2003 MOPEX was adopted as a project of the IAHS/WMO Working Group on GEWEX and of the WMO Commission on Hydrology (CHy), and is now a contributor to the Combined Enhanced Observing Period (CEOP) of the World Climate Research Program (WCRP) In 2004, MOPEX became a Working Group of the IAHS Prediction in Ungauged Basins (PUB) Initiative MOPEX is also expected to contribute to the work of the Hydrologic Ensemble Prediction Experiment (HEPEX) The primary goal of MOPEX is to develop techniques for the a priori estimation of the parameters used in land surface parameterization schemes of atmospheric models and in hydrological models A major early effort of MOPEX has been to assemble a large number of high-quality historical hydrometeorological and river basin characteristics data sets for a wide range of river basins (500-10 000 km 2 ) throughout the world MOPEX data sets are available via the Internet (ftp://hydrologynwsnoaagov/pub/gcip/mopex/US_Data/) This paper documents the development of data sets for river basins in the USA Several highly successful parameter estimation workshops have been organized by MOPEX The first was held as part of the IAHS General Assembly in Birmingham, UK, in July 1999 The second workshop was hosted in April 2002 in Tucson, Arizona, USA, by the SAHRA/University of Arizona The third MOPEX workshop was held as part of the IAHS General Assembly in Sapporo, Japan, July 2003 The fourth, in Paris, France, July 2005 was organized by the CEMAGREF in collaboration with the ENGREF, Meteo France, National Weather Service and the SAHRA/University of Arizona The fifth workshop was held as part of the IAHS Scientific Assembly, February 2005, Foz do Iguacu, Brazil The purpose of the future phases of the project is to: (a) continue collecting additional international data sets; update data from the USA by adding recent years, including data for elevation zones in mountainous areas and refining energy forcing data; (b) continue to conduct international MOPEX workshops; (c) provide leadership to develop a better scientific understanding of how to improve procedures for a priori parameter estimation; (d) make a significant hydrological contribution to CEOP and PUB; and (e) demonstrate transferability of MOPEX results The basic data collection strategy being used in MOPEX is to seek the most readily available and highest quality data first During the next three years, analyses of the available MOPEX data sets by the international scientific community will be emphasized

Groundwater resources sustainability indicators

Abstract: The UNESCO/IAEA/IAH Working Group on Groundwater Resources Sustainability Indicators has been charged with the development of the following activities under the International Hydrological Programme (sixth phase): to prepare a list of groundwater indicators that can be computed at the national and global level, to develop indicator profiles and capacity building materials and to work with case study countries to implement groundwater indicators. In the proposed list of 10 groundwater indicators each of them describes a specific aspect of the groundwater system and/or processes, and is based on aggregation of selected variables, both quantitative and qualitative. Indicators are focused on social, economic and environmental aspects of groundwater resources policy and management, and act as an important communication tool for planners, policy-makers and the public. A balanced scientific and policy-based approach has been employed in deriving groundwater indicators. A DPISR framework was applied in finalizing the set of groundwater indicators.

Trends in river floods : why is there no clear signal in observations?

Abstract: Floods are of great concern in many areas of the world, with the last decade seeing major fluvial flood events in, for example, Asia, Europe and North America. This has focused attention on whether or not these are a result of a changing climate. River flows calculated from outputs from global climate models often suggest that high river flows will increase in a warmer, future climate. However, the future projections are not necessarily in tune with the records collected so far—the observational evidence is more ambiguous. A recent study of trends in long time series of annual maximum river flows at 195 gauging stations worldwide suggests that the majority of these flow records (70%) do not exhibit any statistically significant trends. Trends in the remaining records are almost evenly split between having a positive and a negative direction. This paper discusses factors that influence the results of trend estimates of floods, and that contribute to the general lack of compelling observational evidence of any long-term increase in extreme river flows. Recent results of trend analysis of observed floods are outlined. Expected impacts of indirect anthropogenic climate change are discussed, and a summary is given of the direct impact of man’s influence on river flows in terms of catchment and river management. Different methodologies to detect trends are briefly outlined, and examples are given of how the choice of method can interact with climatological features to result in different estimates of trend. The examples illustrate the effects of using different types of flow indices and different periods of record. The effects on trend estimates of decadal-scale oscillations that have been shown to occur in many river flow records are discussed. Oscillations compound the problem of untangling trends from normal climatic variability as the cycles of the underlying climatic phenomena (e.g. the North Atlantic Oscillation) may also be predicted to change in a greenhouse gas-induced warmer climate. Initiatives to compile networks of pristine catchments with long river flow records are welcomed as a means of keeping scientific objectivity at the forefront of studies of change detection, an area of research riddled by uncertainty and speculation.

SIEREM : an environmental information system for water resources

Abstract: The joint research unit HydroSciences Montpellier (HSM) aims to study hydrological variability on the African continent. SIEREM, an environmental information system for water resources, has been developed at HSM. The POLLEN method was used to design and achieve this successful system. This method is adapted from the OMT (Object Modelling Technique) method, which is specific to the design of environmental information systems. The main part of the analysis technique consists of modelling the data, i.e. identifying the objects of the system, defining their structure and describing their relationships. The information system is then described according to the different services it has to fulfil. This permits one to define the processes asked for by the users and to provide a description of the functions and algorithms. The system is thus divided into sub-systems. Each one is described according to its interface, the piece of software implemented, the managed object classes and the services provided, and the relationships with the other sub-systems. The final result of this information system is a package of different software products. Depending on their rights and needs, the users get specific accesses to information. Each information type, such as a GIS layer or a rainfall chronicle, is managed in every different product of the system. The public can get metadata through the web site, a researcher in the laboratory can work with the data using the Orion software, etc.

Holocene sediment budgets of the Rhine Delta (The Netherlands): a record of changing sediment delivery

Abstract: Holocene sedimentation in the Rhine-Meuse Delta is facilitated by sea-level rise and tectonics, but most important is the result of the sediment flux received through rivers from the hinterland. The majority of Rhine and Meuse sediment entering the delta was trapped between the apex and coastal barrier, at least during the Middle and Late Holocene. It is not known how much sediment was delivered to the delta over longer periods of time (>100 years), or how delivery rates vary over millennial time scales. Increased amounts of sedimentation owing to human land-use change (on top of climatic variability) are expected, but so far it has not been possible to quantify that impact or to establish since when it has been significant. Based on a multitude of subsurface data (borehole database, complementary digital maps, radio-carbon dates), deposited volumes for successive 1000-year time slices spanning the Holocene have been calculated.

Precipitation elasticity of streamflow in catchments across the world

Abstract: Estimates of the sensitivity of streamflow to climate are required to make informed decisions for managing water resources and environmental systems to cope with hydroclimatic variability and climate change. The precipitation elasticity of streamflow (ep), defined as the proportional change in mean annual streamflow divided by the proportional change in mean annual precipitation, is a measure of the sensitivity of streamflow to precipitation. This paper uses a nonparametric estimator to estimate Ep for over 500 catchments across the world. The nonparametric estimator calculates Ep directly from concurrent historical annual catchment precipitation and streamflow data, and is particularly useful for global studies such as this because it does not require the selection of a single hydrological model and calibration criteria that are appropriate for catchments across the world. The results indicate that changes in precipitation are amplified in streamflow. The Ep estimates generally range from 1.0 to 3.0, that is, a 1% change in mean annual precipitation results in a 1-3% change in mean annual streamflow. The higher ep values (greater than 2.0) are observed in southeastern Australia and southern and western Africa, while lower ep values (lower than 2.0) are observed in southwestern South America and at mid and high latitudes in the Northern Hemisphere. There is a relatively strong inverse relationship between ep and runoff coefficient, with higher ep values observed in catchments with lower runoff coefficients. The ep value is also generally lower than 2.0 in catchments with high mean annual streamflow (greater than 500 mm) or mean annual precipitation (greater than 1500 mm), and in cold climates (mean annual temperature lower than 10°C).

Large basin simulation experience in South America

Abstract: This paper presents some applications of the Large Basin Hydrological Model developed in the Instituto de Pesquisas Hidraulicas of the Federal University of Rio Grande do Sul, Brazil (MGB-IPH) in the simulation of different South American basins. The MGB-IPH is a large scale hydrological model, distributed in square grid cells, which represents the processes of interception, soil water storage, evapotranspiration, runoff generation by surface, groundwater and subsurface processes, and flow propagation through the river network. Spatial variability is represented by the distribution of the physical characteristics through the cells all over the basin, relating it to readily available data, mainly from remote sensing. Applications of this model in South America include real time flow forecasts, seasonal flow forecasts, estimation of water availability in places with scarce data, analysis of impacts of multiple hydraulic structures on the hydrological regime and water quality assessment. The paper describes the experience the authors have achieved in large-scale hydrological modelling in South America, highlighting some challenges, successes and failures that were encountered while simulating river basins that are among the largest in the world, and where data availability may be so low as to classify them as ungauged basins.

Inverse modelling of groundwater flow using model reduction

Abstract: This paper describes a reduced model for groundwater flow that reduces the computational burden necessary for inverse modelling. The formulation follows from a projection of the original groundwater flow equation upon a set of basis vectors (i.e. patterns). Those patterns are computed by a decomposition of the covariance matrix for an ensemble of model evaluations. These represent the model behaviour with respect to model forces and a set of estimation parameters. By projecting (mapping) the original equations upon those patterns, a reduced model is obtained that can be used to solve a minimization problem with negligible computational costs. For several synthetic cases this reduced model found the global minimum more efficiently than the original model using adjoints or finite differences.

Long-term trends and runoff fluctuations of European rivers

Abstract: In this paper the occurrence of dry and wet periods for 18 major European rivers during the period 1850-1997 is analysed. Annual discharge series were standardized for three regions: West/Central Europe, East Europe and North Europe, and for the whole of Europe. The statistical analysis of these series did not confirm any long-term increase or decrease in discharge during the last 150 years. Dry cycles of about 13.5 years and 28-29 years were identified. In East Europe the occurrence of the wet and dry cycles are shifted compared to North and West/Central Europe by a few years. Similar periods have been reported in other world rivers (Amazon, Congo) as well as in the Southern Oscillation, North Atlantic Oscillation and Pacific Decadal Oscillation phenomena. The time shift of cycles in different regions is the regularity related to general oceanic and atmospheric circulation.

Drought propagation through the hydrological cycle

Abstract: Time series of simulated recharge, groundwater heads and streamflow were obtained for temperate humid and semiarid climate regions and for quickly and slowly-responding catchments. These were analysed to investigate the propagation of drought through the subsurface, i.e. the change in characteristics (onset, duration and severity) from a meteorological drought to a hydrological drought. In two selected contrasting climate regions (Spain and The Netherlands) the propagation of recharge droughts generally leads to smaller hydrological droughts, except for severe recharge droughts, which might generate very severe hydrological droughts. In quickly-responding catchments more minor droughts will occur, whereas the probability of a very severe drought is higher in slowly-responding catchments. It is anticipated that quantitative knowledge on drought propagation will advance if recharge droughts derived from real instead of synthetic recharge can be better defined, i.e. by use of recharge anomalies.

Regionalization methods in rainfall-runoff modelling using large catchment samples.

Abstract: In ungauged catchments, model parameters are usually transposed from gauged catchments as no runoff data are available for calibrating them. Parameters can be either transposed from nearby catchments or, alternatively, functional relationships between model parameters and available catchment attributes can be derived from gauged catchments that may be further away. This article summarizes the most important methods and recent findings from the literature with a focus on the relative performance of the regionalization methods. As performance is strongly influenced by the local conditions, general findings on the suitability of regionalization methods for a given climate region can only be obtained by analysing a large number of catchments, at the same time. Even with large catchment samples, the differences between the regionalization methods tend to be small. Suggestions for improving current regionalization methods are given.

Assimilation of remotely sensed soil saturation levels in conceptual rainfall-runoff models

Abstract: Owing to the nonlinearity of the rainfall-infiltration-runoff relationship, soil water content in the river basin represents a key environmental variable to be monitored for flood management purposes. In this study an attempt was made to sequentially assimilate into a simple lumped conceptual rainfall-runoff model an estimate of the soil saturation level. The estimate was obtained from: (a) field measurements of water table depth; and (b) backscattering of the radar signal emitted by active microwave sensors on board ERS-1. The assimilation scheme is based on an extended Kalman filter as both simulated and observed soil saturation states are prone to errors. The magnitude of the internal state updating thus depends on the ratio of errors on the observations and the model. The analysis of a series of ERS-1 SAR images showed that hydrologically relevant information could be retrieved from radar imagery by averaging the backscattering coefficient over clusters of pixels for which the sensitivity towards changing moisture conditions is significant. The assimilation procedure is performed on the experimental Alzette River basin (1175 km 2 ). Improvements of model performance through data assimilation demonstrate the usefulness of field measurements and remote sensing observations in flood forecasting applications.

The effect of the Great Flood of 1993 on subsequent suspended sediment concentrations and fluxes in the Mississippi River Basin, USA

Abstract: During the spring/summer of 1993, the upper Midwestern USA experienced unusually heavy precipitation (200-350% above normal). More than 500 gauging stations in the region were simultaneously above flood stage, and nearly 150 major rivers and tributaries over-topped their banks. This was one of the costliest floods in the history of the USA, and came to be known as the Great Flood of 1993. An examination of the long-term daily sediment record for the Mississippi River at Thebes, Illinois (representing the middle, or lower part of the upper basin), indicates that the flood had a severe and long-lasting impact on subsequent suspended sediment concentrations (SSC) and annual suspended sediment fluxes in the basin. At Thebes, pre-1993 (1981-1992) median discharge and SSC were about 5400 m 3 s -1 and 304 mg L -1 , respectively; whereas, post-1993 (1994-2004) median discharge and SSC were about 5200 m 3 s -1 and 189 mg L -1 , respectively. Clearly, the 1993 flood removed substantial amounts of stored bed sediment and/or readily erodible flood plain deposits, eliminating a major source of SSC for the Thebes site. Examination of additional, but discontinuous sediment records (covering the period from 1981-2004) for other sites in the basin indicates that current post-flood declines in SSC and suspended sediment fluxes range from a low of about 10% to a high of about 36%.

Experience from applications of the HBV hydrological model from the perspective of prediction in ungauged basins

Abstract: Since its introduction in the 1970s the HBV hydrological model has been applied in more than 50 countries and it is now a standard tool for hydrologists in the Nordic area It has appeared in many shapes and for a great number of applications Many of these are in basins with poor data coverage or even ungauged basins The latter is, for example, the case in the nationwide hydrological mappings carried out in Finland, Norway and Sweden It has also been used in many river basins where uncalibrated output from a hydrological model is the only realistic option due to shortage of data These results are produced in a rather pragmatic way, with generalized parameter values, but they are much better than nothing Ungauged simulations have opened new possibilities in hydrological modelling In Sweden the total transport of nutrient to the Baltic Sea could be simulated and the step from limited basin studies of impacts of climate change to nationwide assessment was made possible The paper reviews the history of the HBV model with the focus on discussion of prediction in ungauged basins

Changing fluxes of sediments and salts as recorded in lower River Murray wetlands, Australia

Abstract: The River Murray basin, Australia's largest, has been significantly impacted by changed flow regimes and increased fluxes of salts and sediments since settlement in the 1840s. The river's flood plain hosts an array of cut-off meanders, levee lakes and basin depression lakes that archive historical changes. Pre-European sedimentation rates are typically approx. 0.1-1 mm year -1 , while those in the period after European arrival are typically 10 to 30 fold greater. This increased sedimentation corresponds to a shift in wetland trophic state from submerged macrophytes in clear waters to phytoplankton-dominated, turbid systems. There is evidence for a decline in sedimentation in some natural wetlands after river regulation from the 1920s, but with the maintenance of the phytoplankton state. Fossil diatom assemblages reveal that, while some wetlands had saline episodes before settlement, others became saline after, and as early as the 1880s. The oxidation of sulphurous salts deposited after regulation has induced hyperacidity in a number of wetlands in recent years. While these wetlands are rightly perceived as being heavily impacted, other, once open water systems, that have infilled and now support rich macrophyte beds, are used as interpretive sites. The rate of filling, however, suggests that the lifespan of these wetlands is short. The rate of wetland loss through such increased infilling is unlikely to be matched by future scouring as regulation has eliminated middle order floods from the lower catchment.

Propagation of drought in a groundwater fed catchment, the Pang in UK

Abstract: Regional drought characteristics, such as the area covered by drought and the total deficit over that area, are important measures of the severity of a drought event. Gridded, monthly data from the Pang catchment, UK, are analysed here to study the spatial aspects of the drought as it propagates from a meteorological drought, through a drought in the groundwater system and finally appears as a drought in discharge at the catchment outlet. Drought events are derived separately for each grid cell and variable (rainfall, recharge and hydraulic head) using the threshold level method, and combined to yield regional or catchment-specific drought characteristics. The results demonstrate the catchment control in modifying the drought signal from a series of short duration droughts in rainfall covering large parts of the catchment, through fewer and longer droughts in groundwater recharge, head and discharge. The most severe hydrological droughts in the period 1961-1997 occurred in 1975-1977 and 1991-1992. The average area covered by drought is smaller for groundwater recharge than hydraulic head. Hydraulic head and discharge exhibit similar drought behaviour, which can be expected in a groundwater fed catchment.

Numerical estimation of flood zones in the Vistula River valley, Warsaw, Poland.

Abstract: Flood maps (referred to as flood risk maps) are developed for planning purposes and the needs of insurance companies. They usually map the flood with a 100-year recurrence interval (Qpl%, i.e. discharge of probability of occurrence p = 1%), or flooding during the largest historically recorded flood. Typically these maps identify the zone of highest hazard, the so-called flood path, which is where construction is forbidden, and a zone of high hazard, i.e. the area between the flood path and the edge of the Q p 1% flood. In this study the assessment of the flood waters between the flood protection dykes of a reach of Vistula River was made using a one-dimensional hydraulic model and a Digital Elevation Model (DEM). The ordinates of water level for the Vistula were determined with the HEC-RAS model, assuming conditions of a steady state flow with a given probability of exceedence. The flood zones obtained from the simulations indicate that a significant part of the town is situated in the potentially dangerous flood hazard zone. The simulations also indicate that under present conditions the elevations of the flood protection dykes are sufficient to convey the Qp1 % discharge. However, the dykes would not ensure protection of an important part of the city in the case of a Qp0. 1% discharge.

Flood pulses and river ecosystem robustness

Abstract: Du point de vue de l'ecologie fonctionnelle, les rivieres sont considerees comme des systemes ouverts. Cela signifie que leur dynamique en matiere de bilan de matiere depend d'un apport continu en provenance des ecosystemes terrestres. D'un autre cote la qualite de l'eau et la biodiversite dependent principalement des impulsions des crues, qui a leur tour dependent du climat, de la geomorphologie du bassin, du caractere de l'ecosysteme, du developpement du bassin, du rejet de polluants et de l'amenagement de la vallee. La comprehension de l'interaction entre ces composantes est fondamentale pour que les societes beneficient de ressources en eau et de services ecosystemiques durables. L'un des outils les plus puissants pour la gestion de l'eau, peu utilise jusqu'a present, est le potentiel de l'ecosysteme de la plaine d'inondation. Les plaines d'inondation possedent de grandes facultes d'adaptation qui peuvent etre utilisees pour accroitre la capacite de transfert des bassins fluviaux. Le potentiel adaptatif de l'ecosysteme de plaine d'inondation repose sur ses proprietes propres puisque la plaine d'inondation a ete l'ecosysteme traversant toute la gamme des premieres successions d'etats ecologiques. Les etats primitifs et plus encore intermediaires des ecosystemes se caracterisent par un intense prelevement de nutriments et de polluants, ces etats changeant d'annee en annee en fonction de la puissance des impulsions hydrologiques. En tant qu'approche systemique, l'ecohydrologie fournit un cadre conceptuel permettant d'utiliser les proprietes de l'ecosysteme, l'interaction entre hydrologie et biocenose dans la plaine d'inondation par exemple, pour optimiser ses fonctions en vue d'une de l'amelioration de l'autoepuration transformant les nutriments en exces en biomasse et/ou en bioenergie.

Impact of the Amazon tributaries on major floods at Óbidos.

Abstract: Major flooding of the Amazon river (with discharge over 250 000 m 3 s -1 ) is analysed, using daily discharge at (a) Obidos, the lowest gauged station on the Amazon River, 800 km from the ocean, (b) six gauge stations located on the main tributaries and characterized by different discharge regimes. During the 1984-2001 period major flooding on the main stream was related to the following features: (a) greater than usual high water in the Solimoes River, the largest tributary, (b) delayed discharge peaks in the southwestern tributaries and the Amazonas River (Peru) and/or advanced discharge peaks on the Negro-Branco River, (c) unusual February-April discharge peaks in the western and northwestern tributaries, particularly in the Negro River. These two last features contribute to the simultaneous inflow of a great quantity of water from all the tributaries in April-May and may favour major flooding of the Amazon River at Obidos.

Past and future changes in flood and drought in the Nordic countries.

Abstract: Based on a data set of 46 daily streamflow records from the Nordic region for the period 1920-2002 the natural variability in trends and estimated return levels of flood and drought has been studied. In addition, for a subset of series, return level estimates based on historical records were compared to extreme estimates for a control period, 1961-1990, and a scenario period, 2071-2100. It was shown that detected trends and return levels strongly depend on the time period studied because the natural variability in the extremes is large. The scenarios indicated reduced annual floods in eastern Norway, increased annual floods in the western part and varying results for the basins in central and northern Norway. Droughts in general tended to become more severe in the scenarios. The expected changes in floods in the scenarios were only larger than the differences found due to natural variability for one AOGCM-Regional climate model combination.

An underutilized rhsource : Historical flood chronologies a valuable resource in determining periods of hydro-geomorphic change

Abstract: Floods are recognized as important geomorphic drivers within the hydrological system, but short hydrological records can inhibit the application of hydrological data in determining periods of hydrologically driven geomorphic change. This paper details the construction of a series of historical flood chronologies, based on some of the largest catchments within the UK. Flood chronologies have been constructed for eight large UK rivers; the selected sites provide a network covering many of the largest river catchments in the UK centred on cities and towns with long detailed documentary flood histories. These chronologies offer an opportunity to assess the long-term patterns of flooding, indirectly determining likely periods of increased geomorphic activity. This research represents the first coherent large-scale analysis undertaken of historical multi-catchment flood chronologies, providing an unparalleled network of sites across the country, permitting analysis of the spatial and temporal distribution of historical flood patterns on a national scale.

Exploring the impacts of climate change on water resources - regional impacts at a regional scale: Bangladesh

Abstract: Bangladesh is located at the confluence of three major river basins: the Ganges, Brahmaputra and Meghna (GBM) basins. The GWAVA (Global Water AVailability Assessment) model, a global-scale gridded approach to hydrological modelling, has been applied to all GBM basins to investigate the impacts of climate change on water resources at a regional scale. The entire model set-up is composed of a coarse-scale GBM-wide model at 0.5 degrees resolution and a fine-scale model at 0.1 degrees representing Bangladesh. A suite of climate scenarios have been collated from regional climate data using the Hadley Centre’s HadRM2 and that generated by the Indian Institute of Tropical Meteorology using the Hadley Centre’s PRECIS. Scenarios for water demands have been developed for the present and future based on socio-economic data from various publicly available sources and local water management plans. The comparison of water demands with supply using spatial-temporal distributed water availability indices enables areas of future scarcity to be identified.

Glacial erosion and sediment transport in the Mittivakkat Glacier catchment, Ammassalik Island, southeast Greenland, 2005.

Abstract: A station for monitoring suspended sediment concentration with high time resolution was developed and located near the outlet from the Mittivakkat Glacier in order to monitor true glacial erosion. Sediment transport at 10 minute intervals for a 64-day period of the 2005 melt season was determined for the Mittivakkat Glacier catchment, southeast Greenland. The total transport for the whole period was 17 800 t based on measurements with an OBS3 (optical backscatter) sensor and 17 300 t with a Partech IR500 (infrared transmissometer), with maximum transport values of 25 and 24 t 10-min -1 , respectively. The results confirm earlier measurements of specific transport of more than 1000 t km -2 year -1 from the Mittivakkat Glacier. Comparison with concentrations obtained from manual suspended sediment samples from a station near the outlet to the sea, confirm results based on earlier Caesium-137 inventories indicating that sediment is trapped in the proglacial valley between the glacier and the sea. The material produced from glacial erosion is mainly released in late July-August when the glacier drainage system is fully developed and enough melt water is available for transport.

Catalogue of the models used in MOPEX 2004/2005

Abstract: A description of each of the 15 models used in MOPEX (the Model Parameter Experiment), as reported at the MOPEX workshops in 2004 and 2005, is provided. The following models are included: AFFDEF, GR4H, GR4J, HBV, HYDROTEL, IHACRES, MODSPA, MORDOR, NOAH, RRMT, SAC-SMA, SMAR, SWAP, SWB and VIC. Each is described systematically by the original author(s) with details of where the model was first published and of its subsequent use.

Evaluation of a grid-based distributed hydrological model over a large area

Abstract: In this paper we present an on-going effort to utilize available soil moisture data. This study evaluates the performance of a distributed hydrological model using runoff and soil moisture over 75 basins with watershed areas varying from 20 km 2 to 15 000 km 2 . These basins are selected in a region where unique soil moisture data of the Oklahoma Mesonet are available. While simulated runoff is compared to measured streamflow at a basin outlet, simulated soil moisture is compared to basin average soil moisture derived from Oklahoma Mesonet observations. Our results show that the modified Sacramento model driven by a priori parameters performs reasonably well and allows explicit estimation of soil moisture at desired layers. Annual, monthly, and 10-day runoff volumes are found in good agreement with observed data for a range of spatial scales. Simulated and observed soil moisture of the 0-25 cm layer agrees well with a slight (9%) negative bias. However, 25-75 cm layer soil moisture shows a significant (26%) negative bias for most watersheds located in a dry region with P/PE < 0.8.

The decline of hydrological data collection for development of integrated water resource management tools in Southern Africa

Abstract: The Commission for Africa report (2005) recommends a doubling of arable land under irrigation by 2015, and the World Bank water resources strategy (2004) calls for increased investment in water infrastructure in Africa. The NEPAD environment initiative (2003) states that addressing environmental issues is necessary for achieving goals of sustainable growth and development and a lasting solution to the eradication of poverty. Water resource management is clearly recognized as critical to economic development in Africa, but the value of the data on which decisions are based is less well appreciated, with a decline in data collection and management in recent years. The paper reviews the achievements of two regional initiatives to address the data problem and discusses how to use the experience gained for the benefit of future projects.

Investigating the remobilization of fine sediment stored on the channel bed of lowland permeable catchments in the UK.

Abstract: The bed of the main channel system represents an important store of fine sediment in lowland groundwater-fed catchments, in the UK, on account of the deposition promoted by their naturally subdued hydrological regimes, low channel gradients and the reduction of flows caused by water abstraction. Although a number of recent investigations have contributed to an improved understanding of the magnitude and spatio-temporal variability of fine sediment storage, much less is known about the role of remobilization of fine sediment from the channel bed in the suspended sediment fluxes from lowland permeable catchments. To address this shortcoming, the authors report the use of a composite fingerprinting technique, incorporating uncertainty analysis, to investigate the magnitude and timing of the remobilization of fine sediment sequestered on the channel bed of three lowland permeable catchments in the UK. The findings are used to assess the relative contributions of three principal potential sediment sources to the sediment loads sampled at the catchment outlets, namely: fine sediment remobilized from the channel bed of the main stem; suspended sediment inputs from tributary sub-catchments; and sediment originating from channel banks along the main channel.

La variabilité des débits du Rio Amazonas au Pérou

Abstract: Le bassin amazonien peruvien (977 920km 2 , 76% de la superficie du Perou) apporte au Bresil d'importants volumes d'eau. Les debits de l'Amazone au Perou n'etaient pas connus. A partir des series de hauteurs d'eau journalieres aux stations de Tamshiyacu (1983-2005) et d'Iquitos (1969-2005, 50 km en aval) ainsi que des jaugeages realises par ADCP a Tamshiyacu depuis 2001, le debit a Tamshiyacu a ete calcule (1969-2005). Le debit moyen de cette station, la seule jaugee sur l'Amazone au Perou, est 25 000 m3 s -1 . Les donnees de pluie mensuelles de 234 postes pluviometriques ont ete utilisees pour calculer la lame d'eau precipitee (1964-1997). Les precipitations moyennes annuelles sont de 1600 mm. Le relation pluies/debits annuels pour la periode commune 1970-1997 est forte (r 2 = 0.77). On observe une tendance globale decroissante, de -0.83% et -0.81% respectivement pour les pluies et les debits sur la periode de 28 annees etudiees.