Event-based rainfall-driven flooding in Great Britain using Convection Permitting Models

Current flood risk estimates in Great Britain consider the impacts of climate change using uniform rainfall change factors, which fail to capture the spatiotemporal variability of short-duration, high-intensity rainfall that is vitally important for understanding surface water flood risk. The UKCP Local high-resolution (5 km, hourly) convection-permitting rainfall projections, with 12 ensemble members spanning 1980–2080, offer a unique opportunity to improve flood risk assessment in Great Britain. We developed a national-scale LISFLOOD-FP hydrodynamic model to spatiotemporally simulate 120,000 extreme rainfall events across Great Britain, examining how changes in short-duration rainfall influence surface water flood risk at the national scale and how these relationships evolve over time under climate change. We present the first comprehensive assessment of current and future changes in the frequency and severity of surface water flooding across Great Britain. Our results demonstrate the importance of explicitly representing spatiotemporal rainfall variability and its projected evolution in flood risk assessments, and highlight the value of an event-based approach for understanding current and future surface water flood risk in a changing climate.