Warming and Earlier Spring Increase Western U.S. Forest Wildfire Activity
- 1 Scripps Institution of Oceanography, La Jolla, CA 92093, USA.
- 2 University of California, Merced, CA 95344, USA.
- 3 U.S. Geological Survey, La Jolla, CA 92093, USA.
- 4 Laboratory of Tree-Ring Research, University of Arizona, Tucson, AZ 85721, USA.
- * To whom correspondence should be addressed. E-mail: awesterling{at}ucmerced.edu
Abstract
Western United States forest wildfire activity is widely thought to have increased in recent decades, yet neither the extent of recent changes nor the degree to which climate may be driving regional changes in wildfire has been systematically documented. Much of the public and scientific discussion of changes in western United States wildfire has focused instead on the effects of 19th- and 20th-century land-use history. We compiled a comprehensive database of large wildfires in western United States forests since 1970 and compared it with hydroclimatic and land-surface data. Here, we show that large wildfire activity increased suddenly and markedly in the mid-1980s, with higher large-wildfire frequency, longer wildfire durations, and longer wildfire seasons. The greatest increases occurred in mid-elevation, Northern Rockies forests, where land-use histories have relatively little effect on fire risks and are strongly associated with increased spring and summer temperatures and an earlier spring snowmelt.
- Received for publication 17 April 2006.
- Accepted for publication 28 June 2006.
