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Summary This paper presents a review of trend analysis of extreme precipitation and hydrological floods in Europe based on observations and future climate projections. The review summaries methods and methodologies applied and key findings from a large number of studies. Reported analyses of observed extreme precipitation and flood records show that there is some evidence of a general increase in extreme precipitation, whereas there are no clear indications of significant trends at large-scale regional or national level of extreme streamflow. Several studies from regions dominated by snowmelt-induced peak flows report decreases in extreme streamflow and earlier spring snowmelt peak flows, likely caused by increasing temperature. The review of likely future changes based on climate projections indicates a general increase in extreme precipitation under a future climate, which is consistent with the observed trends. Hydrological projections of peak flows show large impacts in many areas with both positive and negative changes. A general decrease in flood magnitude and earlier spring floods are projected for catchments with snowmelt-dominated peak flows, which is consistent with the observed trends. Finally, existing guidelines in Europe on design flood and design rainfall estimation are reviewed. The review shows that only few countries have developed guidelines that incorporate a consideration of climate change impacts. [ABSTRACT FROM AUTHOR]

Summary European water policy developments are essentially linked to the implementation of the EU Water Framework Directive and parent legislation, which is built upon the principle of river basin management planning with the objective of achieving good status for all European water bodies. Recent policy developments in the climate change area call for ‘climate proofing’ of EU actions through mainstreaming of adaptation measures into policies and programmes. These policy trends are very closely related to the capacity to get access to supporting scientific information and to bridge the knowledge gap. This paper is about these features, serving as an introduction to the special issue of Journal of Hydrology on climatic change impact on water: overcoming data and science gaps. [ABSTRACT FROM AUTHOR]

Summary: This paper introduces an approach to route discharge with a variable river flow velocity based on the Manning–Strickler formula within large scale hydrological models. The approach has been developed for the global scale hydrological model WaterGAP and model results have been analyzed focusing on Europe. The goal was to find a method that is simple enough to derive the required parameters from globally available data while being sophisticated enough to deliver realistic flow velocity estimates for a large variety of environmental conditions. The river bed roughness (Manning’s n) is approximated in a spatially explicit way based on topography, the location of urban population, and river sinuosity. The hydraulic radius is estimated from actual river discharge, and river bed slope is derived by combining a high resolution DEM, a 5arc min drainage direction map, and river sinuosity. The modeled river flow velocity has been validated against data of US gauging stations. The representation of lateral transport has clearly been improved compared to the constant flow velocity applied in older model versions. The effect of incorporating variable flow velocities as compared to a constant flow velocity is largest on flood discharge, which generally increases in large rivers. The impact on monthly discharge hydrographs is marginal only. WaterGAP has been driven by three climate change projections for the 2050s to assess climate change impacts on flow velocity, and on the residence time of water in the European river system. Results indicate a decrease in residence times for Northern Europe and an increase for parts of the Mediterranean. [Copyright &y& Elsevier]

Summary: In many cultivated areas of the loess belt in Northern Europe, loamy soils are particularly sensitive to runoff and erosion. Those processes may not be continuous within a catchment, and runoff and erosion responses to rainfall events differ depending on the study scale at which they are examined. Many of the underlying mechanisms of this scale effect are still unknown and/or not well described. The objective of this paper is to identify and quantify the scale effects on runoff and erosion, from the field scale to the catchment scale in the context of the Austreberthe catchment, located in Normandy, in an agricultural area of the loess belt. Based on extensive information compiled at the hillslope and the catchment scales, the runoff and erosion budgets are compared between both scales, showing a more important decreasing effect for erosion (95%) than for runoff (85%) when moving from the hillslope to the catchment scale. The reduction due to the scale change is linear for runoff but not for erosion, underlining the complexity of erosion processes. Comparison of these budgets between both scales shows a significant effect of the vegetation cover as an important connectivity parameter at the hillslope scale, but not at the catchment scale. The importance of the connectivity is also quantified when comparing runoff and erosion budgets between two states of the catchment connectivity: the connectivity without soil and water conservation measures and a modified connectivity (with soil and water conservation measures). This change of connectivity in the catchment was estimated to lead to a decrease in discharge and erosion rates of 50% and 90%, respectively. Finally, the sediment budget analysis from the field to the river basin scale shows that 80% of the mobilised sediments on the slopes are deposited before reaching the Austreberthe River. From the Austreberthe catchment (215km2) to the Seine River Basin (more than 65,000km2 the calculated reduction of the erosion rate is only 25%. In this context, the scale effect is more important on hillslopes, where there is not any permanent river channel and where connectivity depends on rainfall events and landscape organisation, than in catchments drained by perennial rivers. [ABSTRACT FROM AUTHOR]

Summary: The European Alps are one region of the world where climate-driven changes are already perceptible, as exemplified by the general retreat of mountain glaciers over past decades. Temperatures have risen by up to 2°C since 1900 particularly at high elevations, a rate that is roughly three times the global-average 20th century warming. Regional climate models suggest that by 2100, winters in Switzerland may warm by 3–5°C and summers by 6–7°C according to greenhouse-gas emissions scenarios, while precipitation is projected to increase in winter and sharply decrease in summer. The impacts of these levels of climatic change will affect both the natural environment and a number of economic activities. Alpine glaciers may lose between 50% and 90% of their current volume and the average snowline will rise by 150m for each degree of warming. Hydrological systems will respond in quantity and seasonality to changing precipitation patterns and to the timing of snow-melt in the Alps, with a greater risk of flooding during the spring and droughts in summer and fall. The direct and indirect impacts of a warming climate will affect key economic sectors such as tourism, hydropower, agriculture and the insurance industry that will be confronted to more frequent natural disasters. This paper will thus provide an overview of the current state of knowledge on climatic change and its impacts on the Alpine world. [ABSTRACT FROM AUTHOR]

Summary: Bankfull flow is a relevant parameter in the field of large scale modelling especially for the analysis of environmental flows and flood related hydrological processes. In our case, bankfull flow data were required within the SCENES project in order to analyse ecological important inundation events at selected grid cells of a European raster. In practise, the determination of bankfull flow is a complex task even on local scale. Subsequent to a literature survey of bankfull flow studies, this paper describes a method which can be applied to estimate bankfull flow on a global or continental grid cell raster. The method is based on the partial duration series approach taking into account a 40-years time series of daily discharge data modelled by the global water model WaterGAP. An increasing threshold censoring procedure, a declustering scheme and the generalised Pareto distribution are applied. Modelled bankfull flow values are then validated by different efficiency criteria against bankfull flows observed at gauging stations in Europe. Thereby, the impact of (i) the applied distribution function, (ii) the threshold setting in the partial duration series, (iii) the climate input data and (iv) applying the annual maxima series are evaluated and compared to the proposed approach. The results show that bankfull flow can be reasonably estimated with a high model efficiency (E 1 =0.71) and weighted correlation (ωr 2 =0.90) as well as a systematic overestimation of 22.8%. Finally it turned out that in our study focusing on hydrological extremes, the appliance of the daily climate input data is a basic requirement. While the choice of the distribution function had no significant impact on the final results, the threshold setting in the partial duration series was crucial. [Copyright &y& Elsevier]