A new dataset of river flood hazard maps for Europe and the Mediterranean Basin

In recent years, the importance of continental-scale hazard maps for riverine floods has grown. Nowadays, such maps are used for a variety of research and commercial activities, such as evaluating present and future risk scenarios and adaptation strategies, as well as supporting management plans for national and local flood risk. In this paper we present a new set of high-resolution (100 m) hazard maps for river flooding that covers most European countries, as well as all of the river basins entering the Mediterranean and Black Sea in the Caucasus, the Middle East and northern Africa. The new river flood hazard maps represent inundation along 329 000 km of the river network, for six different flood return periods, expanding on the datasets previously available for the region. The input river flow data for the new maps are produced by means of the hydrological model LISFLOOD using new calibration and meteorological data, while inundation simulations are performed with the hydrodynamic model LISFLOOD-FP. In addition, we present here a detailed validation exercise using official hazard maps for Hungary, Italy, Norway, Spain and the UK, which provides a more detailed evaluation of the new dataset compared with previous works in the region. We find that the modelled maps can identify on average two-thirds of reference flood extent, but they also overestimate flood-prone areas with below 1-in-100-year flood probabilities, while for return periods equal to or above 500 years, the maps can correctly identify more than half of flooded areas. Further verification is required in the northern African and eastern Mediterranean regions, in order to better understand the performance of the flood maps in arid areas outside Europe. We attribute the observed skill to a number of shortcomings of the modelling framework, such as the absence of flood protections and rivers with an upstream area below 500 km2 and the limitations in representing river channels and the topography of lowland areas. In addition, the different designs of reference maps (e.g. extent of areas included) affect the correct identification of the areas for the validation, thus penalizing the scores. However, modelled maps achieve comparable results to existing large-scale flood models when using similar parameters for the validation. We conclude that recently released high-resolution elevation datasets, combined with reliable data of river channel geometry, may greatly contribute to improving future versions of continental-scale river flood hazard maps. The new high-resolution database of river flood hazard maps is available for download at (Dottori et al., 2020a).