Rapid Flood Guidance for flash floods – an operational service for England and Wales in summer 2025

Rapid Flood Guidance for flash floods – an operational service for England and Wales in summer 2025

Charlie Pilling, Adrian Wynn, Neil Armstrong, Russell Turner, Julia Perez, Chris Lattimore, Catherine Birch

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. Further tragic rapid-onset events across Europe and globally during 2024 re-enforced the need for improved prediction and communication of rapid flooding to save lives. 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.

During summer 2024, the UK Met Office (UKMO) Expert Weather Hub and the Flood Forecasting Centre (FFC) for England and Wales ran a pilot from May to September to nowcast and warn for intense rainfall and rapid onset flooding. The Expert Weather Hub operated a surge capacity drawing on rapidly updating diagnostics to identify areas of intense convection and flood producing rainfall, as well as other hazards. At the same time, FFC piloted 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 highlighted potentially affected areas of England and Wales to emergency responders. Then as storms broke out and the risk of rapid flooding increased, the detailed output from the Expert Weather Hub was used by the FFC to issue Rapid Flood Guidance to emergency responders at short lead times, less than 6 hours, and possibly less than 2 hours’ notice. 

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. 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. This will also highlight finding and recommendations from the Met Office Summer Forecasting Testbed 2024 which compared 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.

The design of the 2025 operational Rapid Flood Guidance service will be described on the ‘eve’ of its launch May 2025.