Spatiotemporal changes in UK heavy rainfall events not captured by intensity-based methods

Abstract The increasing frequency and intensity of heavy rainfall events driven by climate change poses challenges for flood risk management. In this study, we use a high-resolution, convection-permitting ensemble from the UK climate projections local dataset to explore how the spatiotemporal characteristics of heavy rainfall events may evolve across the UK. Adopting an event-based framework, we analyse 5 km hourly rainfall data from 12 ensemble members and compare changes in future rainfall events to those derived from applying intensity-based scaling factors alone. This comparison allows us to identify aspects of rainfall change that are not captured by shifts in intensity distributions. Our results show that short-duration winter events become increasingly localised, with peak intensities increasing by up to 47%, amplifying flash flood potential. In summer, rainfall events exhibit expanded spatial extents—expanding by 25%–40%—magnifying total precipitation volumes. While we find small changes in the number of clustered events (i.e. heavy rainfall events that occur within a 21 day window), there are large changes to the contribution these have to seasonal precipitation, particularly in summer (7%–11% in the baseline to 11%–16% in future period). These findings highlight new insights into how heavy rainfall may change under future climate conditions, identifying aspects of change beyond intensity increases alone that are relevant for informing current practice for flood risk estimation.