Extreme Winds Alter Influence of Fuels and Topography on Megafire Burn Severity in Seasonal Temperate Rainforests under Record Fuel Aridity

Nearly 0.8 million hectares of land were burned in the North American Pacific Northwest (PNW) over two weeks under record-breaking fuel aridity and winds during extraordinary 2020 fire season, representing a rare example megafires forests west Cascade Mountains. We quantified relative influence weather, vegetation, topography on patterns high burn severity (>75% tree mortality) among five synchronous western Despite conventional wisdom climate-limited regimes that regional drivers (e.g., extreme aridity, synoptic winds) overwhelm local controls vegetation mortality structure topography), we hypothesized remain important influences these rugged forested landscapes. To study influences, developed remotely sensed extent maps for distinct weather periods, thereby isolating effect east severity. Our results confirm wind was major driver megafires, but also both significantly affect even winds. Early-seral primarily concentrated private lands, more severely than their older taller counterparts, entire megafire event regardless topography. Meanwhile, mature stands only especially steeper slopes. Although climate change land-use legacies may prime temperate rainforests to frequently at higher severities has been historically observed, our work suggests future high-severity are likely occur coinciding periods heat,