Do green roofs and spatial resolution influence flood simulation output? – A case study in Malmö, Southern Sweden

Abstract. Over recent years many urban areas have experienced severe floods caused by extreme precipitation events. To avoid the devastating socioeconomic and environmental consequences of such floods, countries have issued laws or recommendations on flood risk assessment in urban planning. However, these laws or recommendations seldom include detailed requirements on input data quality or explicit instructions regarding flood simulation settings, leaving much open to interpretation. To contribute to the solution of this issue, this study focuses on examining the influence of the spatial resolution of input data (e.g., elevation and land cover) on flood simulations for urban densification planning, implementing 100-year return period precipitation scenarios. It also explores the impact of green roofs on flood simulations implementing 10-year and 20-year return period precipitation scenarios within the same context. The results show that spatial resolution may affect simulation output since the areas’ land-cover differs but also because of how edge cells are treated in flow simulations. Green roofs and the drainage from these relieve the ground from being flooded with 20–27% less water.