Abstract/Summary

A new reanalysis-based approach is proposed to examine how reconstructions of extreme weather events differ in warmer or cooler counter-factual worlds. This approach offers a novel way to develop plausible storylines for some types of extreme event that other methods may not be suitable for. As a proof of concept, a reanalysis of a severe windstorm that occurred in February 1903 is translated into a warmer world where it produces higher wind speeds and increased rainfall, suggesting that this storm would be more damaging if it occurred today rather than 120 years ago. Whenever a severe weather event occurs with harmful impacts in a particular region, it is often asked by disaster responders, recovery planners, politicians, and journalists whether climate change caused or affected the event. The harmful impacts are caused by the unusual weather, but climate change may have made the weather event more likely, more severe, or both. In those cases, the harmful impacts may be partly or even mostly due to the change in climate. In some cases, the worst consequences may be due to the vulnerability or exposure of the local population or ecosystems, or due to a combination of many other factors (e.g. Otto et al., 2022). Many methodologies exist to understand how climate change has affected extreme events. These are broadly categorized into risk-based approaches and storyline approaches (Stott and Christidis, 2023). The risk-based approaches assess the change in likelihood and magnitude of a particular class of event (e.g. Stott et al., 2004), whereas storyline approaches consider how climate change may have affected a specific event (Trenberth et al., 2015; Shepherd et al., 2018). Other studies consider the related question of what a plausible worst-case event might look like in a particular climate (e.g. Thompson et al., 2017). Some of these methods are now regularly used to provide attribution statements soon after events occur (van Oldenborgh et al., 2021). Event storyline approaches attempt to quantify how an extreme event would be different in an altered climate. This can be achieved by producing reconstructions of the event as it occurred and in counter-factual cooler or warmer climates and comparing the consequences. Various approaches exist for such analyses, including statistical methods (e.g. Cattiaux et al., 2010), analogues (Ginesta et al., 2023; Faranda et al., 2022), nudging a weather or climate model (e.g. Meredith et al., 2015; van Garderen et al., 2021; Sánchez-Benítez et al., 2022), and forecast-based approaches (e.g. Wehner et al., 2019; Leach et al., 2021). Here, we propose a complementary reanalysis-based approach to translate extreme events into different climates.