Area burned at high severity is increasing in western U.S. forests
Area burned is an imperfect metric of fire activity because it does not consider the manner in which fire burns relative to historical fire regimes. High severity fire is more likely than low-severity fire to result in enduring changes to forests and negatively impact communities, other infrastructure, and municipal water supplies. As such, it is important to study metrics characterizing fire severity in addition to evaluating annual area burned.
Increases in burned area across the western United States since the mid-1980s have been widely documented and linked partially to climate factors, yet evaluations of trends in fire severity are lacking. Forest Service scientists and partners evaluated fire severity trends and their inter-annual relationships to climate for western U.S. forests from 1985 to 2017.
There was an overall eight-fold increase in annual area burned at high severity across all western U.S. forests. The relationships 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.
Key Findings
- Area burned at high severity increased from 1985 to 2017 across most western U.S. forests coincident with warmer and drier fire seasons.
- Climate change could result in more high-severity fire where fuels remain abundant.
- These findings suggest an increased risk of fire-catalyzed conversions from forest to alternative vegetation types.
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