Transfer and extension of experience from urban heavy rain flood risk warning

Abstract The high variability of local intense rainfall events and the short response time of flow in urban catchments demand improved methods in flood warning systems. A key aspect of success is the improvement of short-term forecasts of heavy rainfall by combining ensembles of radar nowcasts with numerical weather prediction ensembles. This paper presents results from this approach in the context of the urban fluvial water management and flood warning system in Hamburg since 2019 and extends its conclusions to other application fields. New challenges from this operational context are being investigated in another research project focusing on the city of Hanover. The topics of improved spatial rainfall data resolution, use of ensemble information from radar nowcasts for pluvial flood warning in connection with sewer load and possible solutions for real-time applications in the urban context are tackled. Experiences from both projects illustrate the importance of applying real-time measurements and ensemble forecasts in connection with a clear open information strategy. Data quality and resolution are crucial aspects in this context, making the combination of different data sources potentially significant for improving the outcome.