Comment on hess-2022-243

Abstract

An event-based approach has been used to explore the potential effects of climate change on the spatial and temporal coherence of widespread flood events in Great Britain. Time series of daily mean river flow were generated using a gridded national-scale hydrological model (Grid-to-Grid) driven by the 12-member ensemble of regional climate projections from UKCP18. Gridded flow series were generated nationally for 30-year baseline (1980–2010) and future (2051–2080) time-slices from which sets of widespread extreme events were extracted. These events were defined as exceeding an at-site 99.5th percentile (equivalent to two days per year) simultaneously over an area of at least 20 km2, allowing events to last up to 14 days. This resulted in a set of 14,400 widespread events: approximately 20 events per year, per ensemble member, per time-slice. Overall, results have shown that events are more temporally concentrated in winter in the future time-slice compared to the baseline. Distributions of event area were similar in both time-slices, but the distribution of at-site return periods showed some heavier tails in the future time-slice. Results were consistent across ensemble members, with none showing significant difference in distribution.