FRHYMAP: Flood Risk and HYdrological MAPping

The general objective of the FRHYMAP project was to integrate within a single mesoscale basin, the transboundary Alzette river basin, the various aspects concerning flooding events, reaching from the hydro-climatological analysis of field data to the risk assessment of socio-economic impacts, taking into account past and future climate and landuse changes. It is shown that although no increasing trend was observed for annual rainfall over the last decades, winter precipitation increased and summer precipitation decreased due to an increase in westerly and southwesterly atmospheric circulation patterns. These changes resulted in higher maximum daily winter streamflow and more frequent groundwater resurgence and thus led to an increased flood hazard. Although the overall regime of the Alzette is more dependent on climate fluctuations, land use changes (mining activities, urbanisation) had a marked effect on the rainfall runoff relationship in some subbasins over the last decades. The development of easily transposable hydrological and hydraulic models allowed to define hydrological hazard producing and hydrological risk exposed areas, even in those areas where long hydrological observation series are lacking. The potential damage of flood scenarios was evaluated via flood risk mapping, based on monetary cost assessment on the one hand and on security deficit analysis on the other hand. The uncertainty analysis reveals that the reliability of these risk maps primarily depends on data quality. In order to increase public awareness about flood issues, an experimental hydro-climatological atlas has been developed, which contains information on the whole chain of processes that are relevant in terms of flood genesis.Irma-Spong