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Area burned at high severity is increasing in western U.S. forests

Date: January 19, 2021

Warmer and drier fire seasons contribute to increases in area burned at high severity in western U.S. forests.


An open, grassy area with a few charred standing dead trees.
After two repeat high-severity fires, this former ponderosa pine forest in northern New Mexico is now dominated by re-sprouting shrubs and nonnative grasses. USDA Forest Service photo by Sean Parks
Area burned is an imperfect metric of fire activity because it does not consider the manner in which fire burns. For example, low severity fire in warmer and drier conifer forests is often considered beneficial because it helps promote resilience to future fire events. Conversely, high severity fire in these forest types, in which most or all trees are killed, is often considered an undesired outcome. 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. Here, we evaluate fire severity trends and their interannual relationships to climate for western U.S. forests from 1985-2017.

Significant increases in annual area burned at high severity were observed across most regions, with an overall eight-fold increase in annual area burned at high severity across all western U.S. 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. The growing prevalence of high-severity fire in western U.S. forests has important implications for forest ecosystems, including an increased probability of fire-catalyzed conversions from forest to alternative vegetation types.

A graph showing annual area burned at high severity in western US forests from 1985-2017. Area increased approximately 8x from 259 km2 in 1985 to 2103 km2 in 2017.

Key Findings

  • Area burned at high severity increased from 1985-2017 across most western U.S. forests coincident with warmer and drier fire seasons.
  • Warmer and drier fire seasons correspond to elevated fire severity and proportion burned at high severity across many western U.S. forests.
  • Continued 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.

News

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Featured Publications

Parks, Sean A. ; Holsinger, Lisa M. ; Panunto, Matthew H. ; Jolly, William M. ; Dobrowski, Solomon Z. ; Dillon, Gregory K. , 2018


Principal Investigators: 
External Partners: 
John Abatzoglou, University of California Merced