Advances and visions in large-scale hydrological modelling: findings from the 11th Workshop on Large-Scale Hydrological Modelling

Large-scale hydrological modelling has become increasingly wide-spread during the last decade. An annual workshop series on large-scale hydrological modelling has provided, since 1997, a forum to the German-speaking community for discussing recent developments and achievements in this research area. In this paper we present the findings from the 2007 workshop which focused on advances and visions in large-scale hydrological modelling. We identify the state of the art, difficulties and research perspectives with respect to the themes "sensitivity of model results", "integrated modelling" and "coupling of processes in hydrosphere, atmosphere and biosphere". Some achievements in large-scale hydrological modelling during the last ten years are presented together with a selection of remaining challenges for the future

TWINLATIN: Twinning European and Latin-American river basins for research enabling sustainable water resources management. Combined Report D3.1 Hydrological modelling report and D3.2 Evaluation report

Water use has almost tripled over the past 50 years and in some regions the water demand already exceeds supply (Vorosmarty et al., 2000). The world is facing a “global water crisis”; in many countries, current levels of water use are unsustainable, with systems vulnerable to collapse from even small changes in water availability. The need for a scientifically-based assessment of the potential impacts on water resources of future changes, as a basis for society to adapt to such changes, is strong for most parts of the world. Although the focus of such assessments has tended to be climate change, socio-economic changes can have as significant an impact on water availability across the four main use sectors i.e. domestic, agricultural, industrial (including energy) and environmental. Withdrawal and consumption of water is expected to continue to grow substantially over the next 20-50 years (Cosgrove & Rijsberman, 2002), and consequent changes in availability may drastically affect society and economies. One of the most needed improvements in Latin American river basin management is a higher level of detail in hydrological modelling and erosion risk assessment, as a basis for identification and analysis of mitigation actions, as well as for analysis of global change scenarios. Flow measurements are too costly to be realised at more than a few locations, which means that modelled data are required for the rest of the basin. Hence, TWINLATIN Work Package 3 “Hydrological modelling and extremes” was formulated to provide methods and tools to be used by other WPs, in particular WP6 on “Pollution pressure and impact analysis” and WP8 on “Change effects and vulnerability assessment”. With an emphasis on high and low flows and their impacts, WP3 was originally called “Hydrological modelling, flooding, erosion, water scarcity and water abstraction”. However, at the TWINLATIN kick-off meeting it was agreed that some of these issues resided more appropriately in WP6 and WP8, and so WP3 was renamed to focus on hydrological modelling and hydrological extremes. The specific objectives of WP3 as set out in the Description of Work are

Application and evaluation of phosphorus and nitrogen loss quantification tools

Årsliste 2004 The report may also be downloaded from EUROHARP web site: www.euroharp.org. Editors, authors and NIVA assume no liability for any loss resulting from the use of this report.The EC funded EUROHARP project encompasses 22 research institutes from 17 European countries (2002-2005). The overall objective of the EUROHARP work is to provide end-users with guidance for an appropriate choice of quantification tools to satisfy existing European requirements on harmonisation and transparency for quantifying diffuse nutrient losses, e.g. to facilitate the implementation of the Water Framework Directive and the Nitrates Directive. The project includes both the assessment of the performance of individual models and the applicability of the same models in catchments with different data availability and environmental condition throughout Europe. The basis for the performance and applicability studies is the compilation of a harmonised GIS/database for all catchment data and the analysis of these data (trends, watercourse retention).Scoumans, O. (ALTERRA, The Netherlands) Silgram, M. (ADAS, United Kingdom

Current practice and recommendations for modelling global change impacts on water resource in the Himalayas

Global change is expected to have a strong impact in the Himalayan region. The climatic and orographic conditions result in unique modelling challenges and requirements. This paper critically appraises recent hydrological modelling applications in Himalayan river basins, focusing on their utility to analyse the impacts of future climate and socio-economic changes on water resource availability in the region. Results show that the latter are only represented by land use change. Distributed, process-based hydrological models coupled with temperature-index melt models are predominant. The choice of spatial discretisation is critical for model performance due to the strong influence of elevation on meteorological variables and snow/ice accumulation and melt. However, the sparsity and limited reliability of point weather data, and the biases and low resolution of gridded datasets, hinder the representation of the meteorological complexity. These data limitations often limit the selection of models and the quality of the outputs by forcing the exclusion of processes that are significant to the local hydrology. The absence of observations for water stores and fluxes other than river flows prevents multi-variable calibration and increases the risk of equifinality. The uncertainties arising from these limitations are amplified in climate change analyses and, thus, systematic assessment of uncertainty propagation is required. Based on these insights, transferable recommendations are made on directions for future data collection and model applications that may enhance realism within models and advance the ability of global change impact assessments to inform adaptation planning in this globally important region

End-to-End Ensemble Modelling for Water Resources Planning Under Uncertainty

A hydrological model ensemble, considering two model structures (CatchMOD and PDM), parameter uncertainty and two contrasting methods for estimating potential evapotranspiration (PET), is developed to investigate the relative significance of different sources of uncertainty for water resources planning in the Thames basin. This model ensemble is driven by an ensemble of UKCP09 probabilistic and Future Flows climate change projections, for the 2030s, 2050s and 2080s, to quantify the projected impacts on a range of metrics of relevance to water resources planners using a water resources system model of London. These sources of supply-side uncertainty are shown to be significant, with the uncertainty associated with the climate change scenarios the largest but hydrological modelling uncertainty, and the method used to estimate PET also shown to be considerable. In terms of overall impacts, the central estimates for the 2030s, 2050s and 2080s are reductions in available resource of around 7%, 11% and 14% respectively. These impacts are shown to equate to economic costs of the order of £360m, £610m and £735m respectively to mitigate such reductions in supply. The range of uncertainty within each time-horizon is large, greater than the differences between the time-horizons, presenting a significant challenge in deciding the level and timing of investments to mitigate emerging risks. As an example, impacts considered reasonably likely by the 2080s (e.g. a central estimate of 14% impact on deployable output using both PET methods) may be as likely by the 2030s (e. g. using only the modified Penman-Monteith PET method). The estimates of future supply reliability are contrasted with demand forecasts and whilst the pressure associated with the latter is shown to be greater, both are significant and subject to large degrees of uncertainty. This thesis also highlights the need for detailed examination of hydrological model structures to provide evidence as to their strengths and weaknesses in their representation of key processes, particularly during droughts. The limitations of the climate change products currently used in the industry, particularly with regards to droughts and estimating changes in PET, are also explored. Significant ongoing research is developing decision-making approaches to support the planning of robust and resilient systems under an uncertain future. This thesis demonstrates that alongside this development, more research is needed to understand, identify and quantify the significant sources of uncertainty that need to be considered as part of the decision-making process