Warmer and Drier Fire Seasons Contribute to Increases in Area Burned at High Severity in Western US Forests From 1985 to 2017

TLDR

Increases in burned area across the western United States since the mid‑1980s have been documented and linked partially to climate factors, yet trends in fire severity have not been evaluated. The study evaluates fire severity trends and their interannual relationships to climate in western US forests from 1985 to 2017. The authors analyze fire severity metrics and climate data across western US forests from 1985 to 2017. Annual area burned at high severity increased eightfold across most ecoregions, and the link to warmer, drier fire seasons suggests climate change will further elevate high‑severity fire, threatening forest ecosystems by increasing the likelihood of fire‑catalyzed conversion to alternative vegetation.

Abstract

Abstract Increases in burned area across the western United States (US) since the mid‐1980s have been widely documented and linked partially to climate factors, yet evaluations of trends in fire severity are lacking. Here we evaluate fire severity trends and their interannual relationships to climate for western US forests from 1985 to 2017. Significant increases in annual area burned at high severity (AAB hs ) were observed across most ecoregions, with an overall eightfold increase in AAB hs across western US forests. The relationships we identified between the annual fire severity metrics and climate, as well as the observed and projected trend toward warmer and drier fire seasons, suggest that climate change will contribute to increased fire severity in future decades where fuels remain abundant. The growing prevalence of high‐severity fire in western US forests has important implications to forest ecosystems, including an increased probability of fire‐catalyzed conversions from forest to alternative vegetation types.