Tackling the ‘Impossible’: Long Lead Time Flood Warnings in Very Fast-Responding Basins
Flash flooding affects millions of people worldwide and, unlike flooding in larger river basins, there is very little time between the rainfall and the flood impact. This provides unique challenges for not just hydrometeorological forecasting but for those trying to alert vulnerable populations to the risk (likelihood and consequence) with adequate lead time for actions to be taken. This session heard from technical experts and disaster management practitioners involved in recent World Bank assignments in Sierra Leone and Niger in which flash flooding is regularly experienced. These assignments have worked with NMHS organisations to help build capacity and understanding of the technical, social, economic and environmental issues of flash flooding. In Sierra Leone, a trial flood guidance system was developed in 2023 using probabilistic convective-scale rainfall forecasting, allowing long lead times. Lessons from this trial and how these could affect other countries will be shared and discussed. A lively and highly informative discussion session was chaired and details recorded on a whiteboard for 20 minutes at the end of session. Contributions were made by David Rogers (World Bank consultant), Prof. Micha Werner (IHE Delft), Mark Harvey (Resurgence), Francis Reffell (CODOHSAPA, Sierra Leone) and Evelyn Mühlhofer (Federal Office of Meteorology and Climatology MeteoSwiss) and others. These related to the importance of partnership between local agencies responsible for emergency response and the establishment of the Flood Risk Task Force in Sierra Leone, the importance of community engagement in devising flood warning communication methods, and ways of solving highly technical forecasting challenging with local agencies facing major resource and technical challenges.
“Forecasting and warning for rapid response flooding in developing countries IS possible – but it is not easy. Important lessons have been learnt in achieving this goal.”
The discussion session recorded the following proposals to address the challenges of long lead time forecasts in fast responding basins in a low-capacity context: Supporting meteorological agencies may need the development of third party developed and operated rainfall forecast systems, since these are complex and need convective-permitting models to provide sufficiently accurate forecasts to provide lead times required. The importance of the ‘Flood Risk Task Force’ established in Sierra Leone that brings together the three main technical and administrative agencies responsible for flood risk and early warning in Sierra Leone (the Met agency, Hydro agency and Disaster Management agency). How communication methods and approaches need to involve ‘end users’ of communication products to determine the format of communication and aspects such as language used, use of symbols over text, and how to encourage the right behaviours ahead of an uncertain forecast. The usefulness of making community walks through flood risk areas to help educate community leaders in flood risk and flood impact reduction. he discussion session recorded the following proposals to address the challenges of long lead time forecasts in fast responding basins in a low-capacity context.
Organized by: JBA Consulting and GFDRR/World Bank
