Full Citation: Westerling, Anthony L.; Hidalgo, H.G.; Cayan, Daniel R.; Swetnam, Thomas W. 2006. Warming and earlier spring increase western U.S. forest wildfire activity. Science 313(5789):940-943.
External Identifier(s): 10.1126/science.1130691 Digital Object Identifier
Location: Western U.S.
Ecosystem types: Forested ecosystems
Southwest FireCLIME Keywords: None
FRAMES Keywords: Black Hills, coniferous forests, ENSO - El Nino Southern Oscillation, fire frequency, fire management, fire suppression, forest management, fuel management, histories, land use, logging, low intensity burns, Oregon, Pinus ponderosa, post-fire recovery, precipitation, season of fire, Sierra Nevada, surface fires, temperature, wildfires, area burned, land surface, ponderosa pine

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

Anthony Leroy Westerling, H. G. Hidalgo, Daniel R. Cayan, Thomas W. Swetnam


Summary - what did the authors do and why?

The authors compared the annual frequency of large wildfires (> 400ha) to hydroclimatic and land surface variables, specifically mean temperature (March-August), timing of spring snowmelt, and fire season length to determine if the fire frequency of large fires has changed and if that change is due to climate factors.


Publication findings:

The authors found that large fire occurrence has been increasing in response to earlier snowmelt and increasingly warmer temperatures in the early spring months in many areas of the West since the early 1980's. Fire season length has increased by 78 days since 1970, and annual area burned has also significantly increased by at least six and a half times over the same time period. These increases and the interannual variability were strongly correlated with average summer temperatures and the timing of spring snowmelt.

The authors suggest that the earlier Spring snowmelt and higher early season temperatures may lead to longer and drier dry seasons, providing increased opportunities for fire ignition and spread, and as temperatures continue to warm, wildfires will become larger and more frequent.

Climate and Fire Linkages

Fire season length has increased by 78 days between the time periods of 1970 to 1986 and 1987 to 2003 due to earlier ignitions and later control dates, as well as longer burning fires.

Large fire occurrence has been increasing in response to earlier snowmelt and increasingly warmer temperatures in the early spring months in many areas of the West since the early 1980's.

Increasingly warm temperatures have significantly increased annual area burned by at least six and a half times between the time periods of 1970 to 1986 and 1987 to 2003. The authors suggest that as temperatures continue to warm, wildfires will become larger and more frequent.

The interannual variability in wildfire frequency had a strong relationship with regional spring and summer temperature. The authors suggest that as temperatures continue to warm, wildfires will become larger and more frequent.

The interannual variability in wildfire frequency had a strong relationship with the timing of spring snowmelt.