A scenario-based modelling approach to implementing nature-based solutions for flood risk mitigation in Hannover

Abstract The EU Nature Restoration Regulation suggests the implementation of green space as nature-based solutions to enhance urban resilience toward increasing climate risks such as extreme precipitation events and floods in Europe. Scenario based approaches enable the evaluation of the potential of specific nature-based solutions to mitigate flood risk in high flood hazard and vulnerable areas. In this study, we explore the flood risks from heavy rainfall and the potential of nature-based solutions implementations in the city of Hannover, Germany. Using the InVEST urban flood risk mitigation model, we modelled the surface runoff from heavy rainfall and assessed the social vulnerability using population and infrastructure data resulting in a flood risk evaluation. To test flood mitigation under nature-based solutions implementations including grass grid pavers and green roofs, we estimated the runoff improvement under three nature-based solutions scenarios following recommendations from the EU Nature Restoration Regulation. Our analysis revealed that Hannover’s inner-city area is particularly flood-prone and socially vulnerable, while peripheral districts are less affected. The combined risk and vulnerability arise from the surface sealing in built-up areas and their higher population density and associated infrastructure. The scenario results demonstrate flood risk reduction potential when combining different nature-based solutions, though on a limited level calling for more explicit and ambitious regulations at EU, regional and local levels.