New extreme rainfall projections for improved climate resilience of urban drainage systems

Abstract

Climate services must provide robust estimates of future changes to precipitation extremes to inform flood risk management and to assess the resilience of existing urban drainage systems in a changing climate. We use an ensemble of convection-permitting UK climate projections, UKCP Local to estimate return levels of 1–24 h precipitation extremes, combining state-of-the-art climate and spatial statistical modelling. We produce low, central and high precipitation return level uplifts at 5 km resolution across the UK. On average across the UK, the 30y return level of 1 and 24 h precipitation is projected to increase by 30–45% and 20–40% respectively by 2070 under RCP8.5, for central-to-high estimates. Uplifts are consistently higher over the northern UK. For 1 h extremes, uplifts here are higher than the official guidance for some parts of the UK, where guidelines pre-date UKCP Local. These spatially-varying uplifts are given for durations out to 24 h with uplifts lower for longer duration extremes. We provide physical explanations for these spatial patterns and the variation with duration. The new uplifts improve on previous official guidance that used a single value for all durations and across most UK nations, and was based on climate models with poor representation of sub-daily precipitation extremes. The results translate the latest UK climate change projections into tailored climate adaptation information useful and suitable for the water industry and flood risk management stakeholders. This is critical for ensuring we benefit from the latest advances in climate modelling and build a society that is resilient to a changing climate.