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Publication Date
1 August 2023

Simultaneous Large Wildfires Will Increase in the Western U.S.

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Projected changes wildfire simultaneity in the Western US, regionalized over 7 administrative divisions used for fire management. Boxplots show increase at multiple return levels and an increase in the length of the season of high simultaneity.

Multiple small fires require more resources to fight than one large fire; wildfire simultaneity therefore affects the availability and distribution of resources for fire management and is considered in decision-making. This study projects the effects of climate change on simultaneous large wildfires in the Western US, regionalized by administrative divisions used for wildfire management.


In all regions, models project a longer season of high simultaneity when wildfires compete for suppression resources, with a slightly earlier start and notably, a later end. Most of the Western US is projected to see numbers of simultaneous 1000+ acre fires that historically occurred once every ten years happening once every five years, or even more frequently. These changes would negatively impact the effectiveness of fire response.


We modeled historical wildfire simultaneity as a function of the fire weather index using statistical models trained on observed climate and fire data over the Western US.  We then applied these models to regional climate model simulations of the 21st century from the NA-CORDEX data archive. The results project increases in the number of simultaneous 1000+ acre fires in every part of the Western US at multiple return periods. These increases are more pronounced at higher levels of simultaneity, especially in the Northern Rockies region.

Point of Contact
Seth McGinnis
National Center for Atmospheric Research (NCAR)
Funding Program Area(s)
Future regional increases in simultaneous large Western USA wildfires
McGinnis, Seth, Lee Kessenich, Linda O Mearns, Alison Cullen, Harry Richard Podschwit, and Melissa S Bukovsky. 2023. “Future Regional Increases In Simultaneous Large Western Usa Wildfires”. International Journal Of Wildland Fire 32 (9). CSIRO Publishing: 1304-1314. doi:10.1071/wf22107.