Autumn and Winter storms over UK and Ireland about 20% wetter due to human-induced Climate Change

The 2023/2024 storm season for the UK and Ireland was exceptionally wet as a whole, as well as ‘hosting’ a notably large number of named storms, some of which led to devastating flooding, with cascading impacts on human health, food production and the cost of living.Here we present a attribution study for the Oct-Mar season, quantifying the role of human-induced climate change on the frequency and intensity of strong winds and heavy rainfall on storm days as well as total precipitation for the season as a whole. The storm severity index (SSI) is used to identify stormy days and as an indication of wind intensity. We use probabilistic attribution methods following the world weather attribution protocol, synthesising trends in observations with climate models and communicating uncertainties. The rainfall associated with storms was found to have become about 20% more intense and that the 2023/24 level has become about a factor of 10 more likely. Climate change was also found to have a strong influence on Oct-Mar precipitation totals, in line with expectations. The influence of climate change on storm winds, was less clear however, with average wind (SSI) on stormy days being found to have decreased slightly. Possible reasons for this will be discussed in the light of relevant literature. We also highlight the importance of vulnerability and exposure information in combination with attribution outcomes to provide recommendations for reduced impacts.