Warming and earlier spring increase western U.S. forest wildfire activity.

Area of Science:

• Ecology
• Climate Science
• Forestry

Background:

• Western United States forest wildfire activity is perceived to have increased recently.
• Previous discussions often emphasized 19th- and 20th-century land-use history's impact on wildfire.
• Systematic documentation of recent wildfire changes and climate drivers has been lacking.

Purpose of the Study:

• To systematically document changes in western United States wildfire activity since 1970.
• To investigate the extent to which climate change influences regional wildfire patterns.
• To compare the influence of climate versus land-use history on recent wildfire trends.

Main Methods:

• Compiled a comprehensive database of large wildfires in western United States forests from 1970 onwards.
• Compared wildfire data with hydroclimatic and land-surface data.
• Analyzed trends in wildfire frequency, duration, and seasonality.

Main Results:

• Large wildfire activity showed a sudden and marked increase in the mid-1980s.
• Observed increases in wildfire frequency, duration, and season length.
• Greatest increases in mid-elevation Northern Rockies forests, strongly associated with warmer temperatures and earlier snowmelt.

Conclusions:

• Climate change, specifically increased temperatures and earlier snowmelt, is a significant driver of increased wildfire activity in western US forests.
• Land-use history has a relatively smaller impact on current fire risks in certain regions like the Northern Rockies.
• The findings highlight the critical role of climate in contemporary wildfire dynamics.