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

Abstract. Continental scale hazard maps for riverine floods have grown in importance in the last years. Nowadays, they are used for a variety of research and commercial activities, such as evaluating present and future risk scenarios and adaptation strategies, as well as a support of national and local flood risk management plans. Here, we present a new set of hazard maps for river flooding that covers most of the geographical Europe and all the river basins entering the Mediterranean and Black Seas in the Caucasus, Middle East and Northern Africa countries. Maps represent inundation along 329’000 km of river network at 100 m resolution, for six different flood return periods. The input river flow data is produced by the hydrological model LISFLOOD, while inundation simulations are performed with the 2D hydrodynamic modelling LISFLOOD-FP. To provide an overview of the skill of the new maps, we undertake a detailed validation exercise of the new maps using official hazard maps for Hungary, Italy, Norway, Spain and the United Kingdom. We find that modelled maps can identify on average two-thirds of reference flood extent, however they also overestimate flood-prone areas for flood probabilities below 1-in-100-year, while for return periods equal or above 500 years the maps can correctly identify more than half of flooded areas. We attribute the observed skill to a number of shortcomings of the modelling framework, such as the absence of flood protections and rivers with upstream area below 500 km2, and the limitations in representing river channels and topography of low land areas. In addition, the large variability of reference maps affects the correct identification of the areas for the validation, thus penalizing 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 improve future versions of continental-scale flood hazard maps. The database is available for download at https://data.jrc.ec.europa.eu/dataset/1d128b6c-a4ee-4858-9e34-6210707f3c81 (Dottori et al., 2020a).