Quantifying the current and future likelihood of the 2022 extreme wildfires weather conditions in France with anthropogenic climatechange

In 2022, southwestern France experienced an exceptional fire season, with a burned area 14 times higher than the 2006–2023 average. Here, we assess how unusual were the fire weather conditions observed during wildfires of different sizes and how anthropogenic climate change (ACC) has altered —and will further alter— the probability of fire-weather conditions associated with the top-3 largest fires in 2022 (Landiras-1: 12,552 ha; Landiras-2: 7,124 ha; La Teste-de-Buch: 5,709 ha).

To do so, we used the daily Fire Weather Index (FWI) computed from the SAFRAN reanalysis (Système d’Analyse Fournissant des Renseignements Atmosphériques à la Neige) —cross-validated with ERA5— and a nationwide fire record dataset (BDIFF, Base de Données sur les Incendies de Forêts en France: 2006–2023). Using the generalized extreme value (GEV) theory, we then quantified the rarity of FWI conditions associated with the top-3 largest fires across different spatiotemporal scales. Our results show that the rarity of those conditions generally increases with the resolution, with return periods increasing from ~6 to ~34 years, from ~22 to ~89 years and from ~6 to ~101 years when moving from the coarser to the finest spatiotemporal scale for Landiras-1, Landiras-2 and La Teste-de-Buch fires, respectively. Finally, we used four GCMs (IPSL-CM6A-LR, CanESM5, MIROC6 and NorESM2-LM) from the CMIP6 DAMIP and ScenarioMIP experiments to examine how ACC has made those FWI conditions more or less probable from 1950–2100. By 2022, ACC had at least doubled the likelihood of those FWI conditions, and will make them, by the end of the century (under SSP2-4.5), at least 10–100 times more probable, depending on the models. Our study underlines the growing influence of ACC in the risk of extreme fires in France across a range of scales.