Evers, C.; Holz, A.; Busby, S.; Nielsen-Pincus, M. 2022. Extreme Winds Alter Influence of Fuels and Topography on Megafire Burn Severity in Seasonal Temperate Rainforests under Record Fuel Aridity. Fire. 5(2): 41. doi:https://doi.org/10.3390/fire5020041
Nearly 0.8 million hectares of land were burned in the North American Paci?c Northwest (PNW) over two weeks under record-breaking fuel aridity and winds during the extraordinary 2020 ?re season, representing a rare example of mega?res in forests west of the Cascade Mountains. We quanti?ed the relative in?uence of weather, vegetation, and topography on patterns of high burn severity (>75% tree mortality) among ?ve synchronous mega?res in the western Cascade Mountains. Despite the conventional wisdom in climate-limited ?re regimes that regional drivers (e.g., extreme aridity, and synoptic winds) overwhelm local controls on vegetation mortality patterns (e.g., vegetation structure and topography), we hypothesized that local controls remain important in?uences on burn severity patterns in these rugged forested landscapes. To study these in?uences, we developed remotely sensed ?re extent and burn severity maps for two distinct weather periods, thereby isolating the effect of extreme east winds on drivers of burn severity. Our results con?rm that wind was the major driver of the 2020 mega?res, but also that both vegetation structure and topography signi?cantly affect burn severity patterns even under extreme fuel aridity and winds. Early-seral forests primarily concentrated on private lands, burned more severely than their older and taller counterparts, over the entire mega?re event regardless of topography. Meanwhile, mature stands burned severely only under extreme winds and especially on steeper slopes. Although climate change and land-use legacies may prime temperate rainforests to burn more frequently and at higher severities than has been historically observed, our work suggests that future high-severity mega?res are only likely to occur during coinciding periods of heat, fuel aridity, and extreme winds.