Towards Improved Flood Forecasting: Evaluation of Discharge Forecasts Driven by New Rapid-Update Precipitation Forecast Products of DWD

In Germany, flooding in small catchments, driven by locally intense convective precipitation, has caused significant damage and in some cases fatalities in recent years. To ensure more accurate and timely operational flood forecasts and warnings, the regional German Flood Forecasting Centres require improved precipitation forecasts for short-term forecast ranges.

In this context, the ICON Rapid Update Cycle (RUC) of the well-established, high-resolution (2.2 km) regional German numerical weather prediction model ICON-D2 represents a promising approach. The RUC forecasts have been developed by the German Meteorological Service (Deutscher Wetterdienst, DWD) within the framework of SINFONY (Seamless Integrated Forecasting System). They are operationally available since summer 2024. Compared to the standard ICON-D2 model, the RUC— both deterministic and probabilistic — feature an improved two-moments microphysics scheme to better represent strong convective events, hourly updates (instead of three-hourly), a forecast horizon of 14 hours (compared to 48h), and earlier availability for users due to a reduced computation time.

Evaluating the impact of these “rapid update” characteristics on flood forecasting is one of the key objectives of the project “Co-Design of Innovations between Weather and Flood Forecasting”, which aims to strengthen the collaboration between the DWD and the regional German Flood Forecasting Centres. As part of this initiative, the Flood Forecast Centre of the State Institute for Environment Baden-Württemberg (HVZ LUBW) has been investigating the use of the RUC products for hourly operational discharge forecasting, using the distributed water balance model LARSIM (Large Area Runoff Simulation Model).

This contribution presents a verification of discharge forecasts for a large number of gauging stations in Baden-Württemberg during the summer 2024 flood events in south-western Germany. Discharge hindcasts driven by ICON-D2 and ICON-D2 RUC products were performed and systematically compared. The analysis includes both event-based case studies and an overall statistical evaluation.