Even Modest Climate Change Means More and Larger Fires

SEATTLE, Washington, August 31, 2004 (ENS) - The area burned by wildfires in 11 Western states could double by the end of the century if summer climate warms by slightly more than a degree and a half, say researchers with the U.S. Department of Agriculture Forest Service and Pacific Northwest Climate Impacts Group at the University of Washington.

Montana, Wyoming and New Mexico appear acutely sensitive, especially to temperature changes, and fire seasons there may respond more dramatically to global warming than in states such as California and Nevada.

Researchers have developed statistical relationships between observed climate and an 85 year record of fire extent during the 20th century and used them in conjunction with existing state-of-the-art global climate models.

Fire breaks out in Wyoming's Bridger-Teton National Forest. (Photo courtesy National Interagency Fire Center)

"Such increases could have consequences for threatened and endangered species in ecosystems that experience increased fire because many such species are already restricted to specialized and fragmented habitat," he warned.

McKenzie is lead author of "Climatic Change, Wildfire and Conservation," in the August issue of "Conservation Biology." His co-authors are Ze'ev Gedalof of the University of Guelph in Ontario, David Peterson of the USDA Forest Service, and Philip Mote, University of Washington climate scientist and Washington state climatologist.

All are members of the University of Washington's Pacific Northwest Climate Impacts Group.

Today, the forecast is for high pressure that will continue to build into the western states, allowing hot and dry conditions to persist through the day. The National Interagency Fire Center reports very high to extreme fire indices in Alaska, Arizona, California, Colorado, Nebraska, Nevada, South Dakota, Utah and Wyoming.

The authors' analysis of past climate and fire histories showed that the most important variable is hot summer temperatures, more important than precipitation in most cases.

Using what is considered a low end climate change scenario - a 1.6 degree Celsius increase in summer temperatures between 2070 and 2100 compared to temperatures from 1970 to 2000 - the area burned will increase by 1.4 to five times in western states except California and Nevada, where the increase is not so great.

On the front lines of Montana's Bitterroot fire, summer 2000. (Photo courtesy NIFC)

Parts of Northern California where warmer climate could affect the number and extent of fires, for example, are offset by areas in Southern California where fires are almost all caused by human activities and the combination of high temperatures and dry air associated with the Santa Ana winds, not temperature by itself, McKenzie says.

At the other extreme are Montana, Wyoming and New Mexico. Montana is the most sensitive, with the models predicting a five-fold increase in mean area burned over the observed range in climate, the authors write.

In Washington and Oregon, the effects will be intermediate because precipitation and temperature are both associated with fire extent in these states, rather than temperature alone.

More frequent, more extensive fires in forest ecosystems will likely reduce the number and size of patches of older forests, the authors say. Corridors of wild areas between forests, through which species might migrate if their home territory goes up in flames, also could be affected, possibly eliminated.

"The winners after fires in these cases are the weedy, adaptive, quickly reproducing species," McKenzie says. "The losers are the ones needing more stable environments."