en.Wedoany.com Reported - The UK Flood Forecasting Centre (FFC), a partnership between the Environment Agency and the Met Office, has stated that the number of properties at high risk from surface water flooding in England and Wales is three times that of properties at high risk from river and sea flooding.

The risk of surface water flooding has been upgraded in the National Risk Register 2023, with its impact score raised to "significant," placing it on par with river and coastal flood risks and making it one of the highest environmental risks facing England. Climate change is leading to an increase in short, intense summer rainfall, making previously inconvenient flood events more deadly. In the future, more areas may experience flooding for the first time, particularly in developing areas with growing populations.

Recent cases, such as the surface water flooding events in Coverack in 2017 and London in 2021, highlight the importance of improving forecasting. To this end, the Surface Water Flood Forecasting Improvement Project (SWFFIP), a three-year initiative, has enhanced the national capability to forecast surface water or rapid flooding events.

The project supported the design and operational launch of the Rapid Flood Guidance (RFG) service and led to a commitment to extend this service until 2028. Concurrently, the project aimed to improve forecaster tools to generate more accurate and actionable forecasts, including enhancements to the FFC's Surface Water Flooding Hazard Impact Model (SWFHIM). This model helps forecasters understand where surface water flooding is most likely to occur within the next three days, and a proof-of-concept trial for a surface water flood model nowcasting tool was conducted.

Developed in 2020 by the National Hazards Partnership (NHP) to improve impact forecasting, SWFHIM currently provides forecasts of surface water flood risk for approximately six hours to three days ahead. The model integrates surface water runoff forecasts from the Grid-to-Grid national hydrological model developed by the UK Centre for Ecology & Hydrology (UKCEH), which uses Met Office rainfall forecasts; detailed surface water flood maps from the Environment Agency's NaFRA; and a receptor impact database from the Health and Safety Executive (HSE) at a 1km grid scale, covering properties, people, transport, and infrastructure. Forecasts are displayed on a dashboard, showing the likelihood of impact for each county under different flood levels.

The current RFG service uses detailed short-term storm forecasts (convective nowcasts) from the Met Office's Expert Weather Hub, supported by FFC hydrometeorologists, but does not yet include real-time hazard and impact modelling. To address this gap, the FFC trialled two new surface water flood hazard and impact modelling tools for the 0 to 6-hour lead time: SWFHIM and FOREWARNS. Phase one was conducted on the Met Office summer testbed in 2024, and phase two in 2025 focused on operational environment teams. The trials found that both tools aided objective decision-making during the RFG generation process, establishing a basis for future investment in surface water flood modelling tools.

Based on the trial results, recommendations include: continuing to advance performance improvements for SWFHIM and FOREWARNS with scientific partners (including Met Office next-generation rainfall nowcast data, available from 2027); prioritising the development of the SWFHIM nowcasting tool to provide probabilistic outputs within the 0 to 6-hour lead time; considering the implementation of FOREWARNS as an operational prototype; and implementing an automated verification method for surface water hazard and impact models. The FFC plans to incorporate these recommendations into a three-year project, aiming to bring new tools into operational use by 2029 to improve the accuracy and timeliness of the RFG service.

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