Fire weather waves drive extreme fires globally

Fire weather waves (FWWs), episodes of persistent extreme fire weather akin to heat waves, 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. Accounting for only 4% of days during 2002–2024 in forested ecoregions, FWWs coincided with 26% of the area burned, and half of the top 1% of energetic fires ignited on FWW days. Compared with grassland and shrubland fires, forest fires exhibit a larger and more persistent increase in daily burned area in response to FWWs, particularly in Mediterranean forests. FWWs intensify fire activity by sustaining warmer, drier, and windier conditions compared to non-FWW periods – facilitating chronic periods of favorable fire weather that promote fire spread. 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 underscore forecasted FWWs as an important component of early warning systems to strengthen preparedness for extreme forest fires.