Rapid Flood Guidance for flash floods – a trial service for England and Wales, summer 2024

Flash floods, or rapid response catchment flooding, can be defined at flooding impacts between 0-6 hours of impactful rainfall occurring. Nowcasting can be defined at the 0-2 or 0-6 hour time scale. To save lives, warnings at these very short lead times, whether they are for urban areas or ravines, need to be issued rapidly to a receptive customer base.

The Met Office Expert Weather Hub (formally guidance unit) is operating a surge capacity this summer drawing on rapidly updating diagnostics to identify areas of intense convection and flood producing rainfall, as well as other hazards.

At the same time, the Flood Forecasting Centre (FFC) is piloting a Rapid Flood Guidance Service where days 1 and/or day 2 of the daily Flood Guidance Statement are highlighted as susceptible to rapid flooding. This will highlight potentially affected areas of England and Wales to emergency responders. Using the detailed output from the Expert Weather Hub, the FFC will issue Rapid Flood Guidance to emergency responders at short lead times, less than 6 hours, and possibly less than 2 hours’ notice. 

In addition, the Met Office are running a summer forecasting testbed which will explore two rapid surface water flooding hazard impact models. The Surface Water Flooding Hazard Impact Model, SWFHIM, was developed through the Natural Hazards Partnership and is currently used operationally in the FFC. The second, FOREWARNS, has been developed by the University of Leeds and the Met Office.

This presentation will explain the components of the Rapid Flood Guidance trial and present key findings from research to operations, as well as a summary of the evaluation from the hundreds of emergency responders who have already signed up for the trial. It will also highlight key findings from the evaluation of the surface water impact models, with a focus on less than 24 hours lead time. We will highlight development areas to the science and operational development, and suggest how such short notice warnings can best be communicated to potential users to incite the appropriate actions.