European flood awareness system : a technical assessment of CEMS EFAS performance during the floods in Northern Germany in December 2023/January 2024

In December 2023 and January 2024 extensive flooding occurred in Northern Germany in the Ems, Weser and Elbe catchments. The European Flood Awareness System (EFAS) of the Copernicus Emergency Management Service (CEMS) aims to inform the authorities of possible upcoming floods. This report verifies the performance of EFAS service with regard to forecast accuracy; communication clarity and timeliness. EFAS issued 17 notifications (11 Formal Notifications, 5 Informal Flood Notifications, and 1 Flash Flood Notifications). Notifications for riverine flooding were issued for the Ems and Hase (Ems catchment), Ilmenau, Ohre, Sude, Biese and Muritz-Elde (Elbe catchment), and Weser, Aller and Leine (Weser catchment). A Flash Flood notification was issued for the Braunschweig region. Moreover, one pre-tasking request of satellite image acquisition was completed for the Ilmenau, Weser and small tributaries to the Aller (Elbe and Weser catchment). The analysis demonstrated an overall good performance of the service, however, forecast accuracy and lead-time could be improved for some of the rivers. Furthermore. Some inaccuracies occurred in the application of the operational protocol. This report identified actions to further improve the service. These actions include the continued update of the hydrological model set-up to improve forecast accuracy; more streamlined protocols for notifications and pre-tasking to support the issue of timely alerts during complex flood events in large areas.