Atmospheric patterns associated with sub-daily rainfall extremes in western Europe

Abstract

Large-scale atmospheric conditions are a significant driver of rainfall extremes. However, little attention so far has been devoted to understanding how large-scale circulation patterns influence sub-daily rainfall extremes. Using a gauge-based sub-daily rainfall dataset, we investigate the relationship between large-scale circulation and 3-hour extremes for western Europe. A set of 30 weather patterns (WPs) developed by the UK Met Office and reanalysis data of geopotential height at 500hPa (z500) are used to represent large-scale atmospheric conditions. Strong associations with 3hr extremes are found for a small number of WPs: over 50% of 3hr rainfall extremes across Western Europe occur with just 5 WPs. Composites of z500 reveal the WPs resulting in southerly or south-westerly flow along the leading edge of a trough, accompanied by a ridge to the east or northeast, are most favourable for sub-daily rainfall extremes, with a statistically-significant difference between the atmospheric conditions on WP + sub-daily rainfall extreme event days compared to WP non-event days. Given that large-scale circulations are predictable much further in advance than individual extreme rainfall events, these identified relationships could therefore have important implications for forecasting, aiding in the early identification of periods with increased risk of short-duration rainfall extremes.