Name: Hayley Fowler

Talk Title: Using Spatial Extreme Statistics to Provide Climate Uplifts for Flood Risk Management

Abstract: Managing the changing risk of flash floods in urban drainage infrastructure commonly uses a simple percentage climate uplift to the derived design guidelines. However, much of this guidance globally is based on projections from coarse-resolution global or regional climate models with parameterised convection, which underestimate the intensity of short-duration rainfall extremes and their future intensity increases. Here we use a 12-member 2.2km convection-permitting climate model (CPM) ensemble, UKCP Local, at a resolution consistent with weather forecasting. CPMs improve the representation of precipitation extremes; thus, UKCP Local is particularly useful for water stakeholders (water utilities and flood risk management professionals) in managing changing hazards and risks for adaptation planning in wastewater and flood risk management. Diagnosing return level ‘uplifts’ for such high-resolution model simulations is difficult due to both their spatial-temporal variability and correlation across space and time. We develop a spatial extreme statistical model that incorporates spatial-temporal variability and correlation of precipitation extremes to provide robust estimates of uplifts for high return levels across all of the UK for months and seasons of interest. The limitations of the climate upl ift approach, and potential improvements, will also be discussed.