Fire Weather Waves Fuel Extreme Fire Activity

Fire weather waves (FWWs), defined as persistent extreme fire weather, can elevate extreme fire danger by sustaining favorable burning conditions over multiple consecutive days. Here, we examine the relationship between FWWs and fire activity, as well as the patterns and trends of FWWs across global terrestrial ecoregions. In forest ecoregions during 2002–2023, although FWWs accounted for only 9% of days, 29% of all fires ignited on FWW days, and over half of the top 1% largest fires ignited on FWW days, with hotspots observed in temperate and boreal regions. Fire activity strongly responds to FWWs, facilitated by warmer, drier, and windier conditions. In Mediterranean forests, for example, the daily average burned area during the 1 to 7 days following FWW onset is 2 to 3 times that during the 3 days preceding FWWs. FWWs have become, and are projected to become, more frequent, persistent, and severe, with a twofold increase in FWW days projected for 2076–2100 compared to 1979–2024. These findings highlight the potential of FWWs to enhance extreme fire prediction.