Adaptation is cost-effective to offset rising river flood risk in Europe

Abstract River flooding in Europe could rise to unprecedented levels due to global warming and continued development in flood-prone areas. Here we appraise the potential of four key adaptation strategies to mitigate flood risk across Europe based on detailed flood risk modelling and cost-benefit analysis. We find that reducing flood peaks using retention areas is economically the most attractive option. In a scenario without climate mitigation, they can lower projected flood losses in Europe by the end of the century from 42 to 7.5 €billion/year and population exposed by 81%, or achieve a risk level comparable to today. This would require an investment of 2.9 €billion/year over 2020-2100, with a return of 4€ for each 1€ invested. The risk-reduction potential of economically-optimised strengthening of dykes is somewhat lower with 71% for a comparable annual investment. These measures avoid floods to happen and their cost-effectiveness increases with the level of global warming. Implementing building-based flood proofing measures and relocating people and assets are less cost-effective but can reduce impacts in localized areas.