A succession of storms reaching southern England in the winter of 2013/2014 caused severe floods and £451 million insured losses. In a large ensemble of climate model simulations, we find that, as well as increasing the amount of moisture the atmosphere can hold, anthropogenic warming caused a small but significant increase in the number of January days with westerly flow, both of which increased extreme precipitation. Hydrological modelling indicates this increased extreme 30-day-average Thames river flows, and slightly increased daily peak flows, consistent with the understanding of the catchment’s sensitivity to longer-duration precipitation and changes in the role of snowmelt. Consequently, flood risk mapping shows a small increase in properties in the Thames catchment potentially at risk of riverine flooding, with a substantial range of uncertainty, demonstrating the importance of explicit modelling of impacts and relatively subtle changes in weather-related risks when quantifying present-day effects of human influence on climate.
N Schaller, A Kay, NR Massey, GJ van Oldenborgh, FEL Otto, SN Sparrow, R Vautard, P Yiou, I Ashpole, A Bowery, S Crooks, K Haustein, C Huntingford, ..., MR Allen. Human influence on climate in the 2014 southern England winter floods and their impacts
published, Nature Climate Change, 2016