Megafires in Mediterranean Europe: the compound role of fire weather and drought

Abstract Large wildfires and megafires in Mediterranean Europe cause disproportionate social, ecological and economic impacts, yet the processes that allow some ignitions to grow into landscape-scale events remain poorly quantified. Here we analyse 11,403 summer wildfires across Mediterranean Europe during 2008–2022, classified into medium (30–100 ha), large (100–1000 ha), very large (1000–10,000 ha) and megafires (≥10,000 ha). Combining official fire perimeters with a high-resolution environmental and drought dataset, we quantify how fast-reacting weather and slow-reacting fuel and drought indicators jointly control transitions between fire-size classes. Very large fires are preferentially associated with anomalously hot, windy conditions acting on stressed fuels and multi-month drought, whereas the transition to megafire size is closely associated with unusually warm nights and strong winds near ignition. Using Random Forest classifiers and logistic regression, we show that these transitions are predictable from a small set of interpretable variables, including nighttime land-surface temperature, wind speed, and 3-month standardized precipitation–evapotranspiration index. Model performance indicates that up to two-thirds of megafires are correctly identified out of sample. Our results highlight that megafires in Mediterranean Europe emerge from the alignment of preconditioned fuels with exceptional short-term fire weather and emphasize the need to jointly manage fuel continuity and anticipate periods of persistent hot, dry and windy conditions in a warming climate.