An increasingly hot climate seems to have amplified forest wildfire activity in the western United States over the last 35 years, researchers say.

Anthony Westerling and colleagues at the Scripps Institution of Oceanography in La Jolla, Calif. compiled a database of large forest wildfires in the region for the period from 1970 to 2003.

They compared those data with corresponding measurements of climate, land-surface conditions and hydrology, or water distribution.

They found that wildfire activity increased suddenly in the mid-1980s, with large fires becoming more frequent, fires becoming longer, and the wildfire season also becoming longer.

The findings appear in the July 7 issue of the research journal Science.

The results indicate that fires and “hydroclimate,” which involves spring and summer temperatures as well as snowmelt, are closely related, the scientists said.

They also suggested that climate variation has been the main cause of the increase in fires during the period of their study, although land-use changes may also be implicated.

Temperatures are gradually rising globally as a result of human burning of fossil fuels, which releases heat-trapping gases into the atmosphere, according to most experts. Scientists have also suggested global warming may be causing increases in hurricane intensity. A report last month from the U.S. National Academy of Sciences said the Earth’s surface has been hotter during the past few decades than at any comparable period in the past four centuries.

It is unclear whether the warming tied to the increased wildfires is part of the larger global warming phenomenon, Westerling and colleagues said. But either way, forecasts of further global warming mean the fires will probably keep getting worse, they predicted.

“Western United States forest wildfire activity is widely thought to have increased in recent decades, but surprisingly, the extent of recent changes has never been systematically documented,” the researchers wrote. “Nor has it been established to what degree climate may be driving regional changes in wildfire.”


- Courtesy Science
and World Science staff

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