Table S2.

Fire season start (first quartile, Julian day), median discovery day (Julian day) and fire season length (IQR, in days) by ecoregion and averaged across the entire coterminous United States

EcoregionFire season start (Julian day)Human advancement (d)Median discovery day (Julian day)Human advancement (d)Fire season length (IQR, days)Human expansion (d)
HumanLightningHumanLightningHumanLightning
Coterminous United States811821011402066615446108
Eastern Temperate Forests69149801111817016766101
Great Plains84181971632074414847101
North American Deserts1291875817820729924052
Temperate Sierras1261805416620135853946
Tropical Wet Forests641538910717568985246
Mediterranean California1612014019822628854540
Northwestern Forested Mountains175196212122153753639
Marine West Coast Forest18419410218217NA675215
Southern Semiarid Highlands1241734915119241554114
Northern Forests10514843120196765179NA
  • Note that the national-scale tripling of fire season length by human ignitions is driven by earlier (spring) fires in eastern ecoregions coupled with later (fall) fires in western ecoregions.