The potential of green infrastructure in urban pluvial flood mitigation – a scenario-based modelling study in Berlin

Abstract. Urban surface sealing limits infiltration and thus increases the formation of runoff during heavy rain events. Green infrastructure (GI) measures can be used to reduce urban flood risk by promoting decentralized infiltration, water storage and evapotranspiration. With a scenario-based modelling study, we investigate the impact of green infrastructure on urban runoff formation, flood water depths and the resulting damage to buildings; comparing it with the impact of the conventional drainage system. The study area is located in the city of Berlin, in a heavily sealed 3.3 km² urban catchment. Design rain storms with a duration of one hour and totals between 15 and 100 mm are considered. The green infrastructure scenarios include different spatial extents and combinations of bioretention systems, green roofs and pervious pavement. The Storm Water Management Model is used for the urban runoff generation and the 2D-hydrodynamic module of TELEMAC for surface runoff concentration. Building damage is modelled with the Flood Damage Estimation Tool, a recursive partitioning tool developed with survey data representative of building damage caused by pluvial floods. Flood mitigation is investigated regarding absolute and relative reduction and also space efficiency of the GI types. Relative flood mitigation reduces at all modelling steps with increasing rain totals. In contrast, absolute runoff reduction increases with increasing rain totals while the area with maximum water level > 10 cm decreases the most at the 49 mm event and building damage reduces most at 25–30 mm. Bioretention systems achieve the highest spatial efficiency, however, green roofs and pervious pavements do not impede the former land use.