Megafires in a Warming World: What Wildfire Risk Factors Led to California’s Largest Recorded Wildfire

Massive wildfires and extreme fire behavior are becoming more frequent across the western United States, creating a need to better understand how megafire will evolve in our warming world. Here, spread model Prometheus is used simulate initial explosive growth of 2020 August Complex, which occurred northern California (CA) mixed conifer forests. High temperatures, low relative humidity, daytime southerly winds were all highly correlated with rates modeled spread. Fine fuels reached very dry levels, accelerated simulation heightened heat release (HR). Model sensitivity tests indicate that HR most sensitive aridity fuel moisture content. Despite impressive early observed fire, shifting ignition September heatwave predicted >50% increase HR, as well increased nighttime activity. Detailed analyses develops can help personnel prepare for problematic ignitions.