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Ain’t no mountain high enough: Why fires are climbing higher than ever before due to increased western aridity

Date: April 28, 2022

As the west has become more arid the occurrence and size of wildfires has increased—especially in high elevation forests.

In areas like in high elevation western, mountainous regions with an abundance of moisture, snowpack, and cooler temperatures, fire has historically been less common. This study portrays a changing paradigm in fire’s ability to spread rapidly in high-elevation environments such as in the Sierra Nevada, the Pacific Northwest, and the Northern Rockies. This study documents a startling upslope trend for the fires of the United States—burning up territories that historically have been too wet, snowy, or high to burn—due to an increase in forest aridity.

Two graphics showing changes in vapor pressure deficits (aridity) with regard to elevation and burned areas.
Increases in high-elevation forest fire activity in response to increasing vapor pressure deficit (aridity) by elevation and burned area.

While historical fire exclusion policies have had a strong effect on lower elevation forests, where fire was once a frequent visitor, past fire suppression has had less ecological effect on these high elevation forests where fire was rare and localized when it occurred. The reduced precipitation frequency and warming associated with climate change are effectively changing the fire regime of higher elevation forests. High elevation forests comprise species and fuels where crown fires can readily spread, and the shift in climate suggests that fuel treatments here could be as appropriate as in forests where management intervention in fire has led to fuel accumulations, particularly in proximity to inhabited areas.

This research examines changes in the elevational distribution of burned forests across western regions of the United States—and how climate change affects this new shift in high-elevation fire activity. Fifteen mountainous areas of the United States were explored, using historical documentation from wildfire activity. This activity was measured only in areas where fires burned greater than 405 ha (1000 ac) from1984 to 2017. Researchers also used a 10-m-resolution digital elevation model and daily high-spatial-resolution surface meteorological data.

The study observes changes in upslope advance in high-elevation forest fires, how climate aridity—and our warming planet—is correlated with these fires, and how biodiversity loss and vegetation conversion factor into these changing conditions. These changing conditions have significant implications for carbon storage, snowpack, and the western United States’ water quantity and quality.

Key Findings

  • Climate-driven changes in global temperatures and aridity are directly correlated with the decreasing interval between high-elevation fires.
  • Fire activity is increasingly disproportionate at higher elevations than that of lower elevation forests in the Western United States.
  • Studies documented an upslope advance of high-elevation fires of roughly 7.6 m (25 ft) per year.
  • An additional 81,500 km2 (31,500 miles2) of the western United States forested regions were exposed to fires due to increased aridity between 1984 and 2017.

Featured Publications

Alizadeha, Mohammad Reza ; Abatzoglou, John T. ; Luce, Charles H. ; Adamowski, Jan F. ; Farid, Arvin ; Sadegh, Mojtaba , 2021

Principal Investigators: 
Principal Investigators - External: 
Mohammad Reza Alizadeh - McGill University - Canada
External Partners: 
John T. Abatzoglou, University of California – Merced
Jan F. Adamowski, McGill University
Arvan Farid, Boise State University
Mojtaba Sadegh, Boise State University
Research Location: 
Western US