Large forest fires have occurred more frequently in the western United States since the mid-1980s as spring temperatures increased, mountain snows melted earlier and summers got hotter, according to new research.
Almost seven times more forested federal land burned during the 1987-2003 period than during the previous 17 years. In addition, large fires occurred about four times more often during the latter period.
The research is the most systematic analysis to date of recent changes in forest fire activity in the western United States. The increases in fire extent and frequency are strongly linked to higher March-through-August temperatures and are most pronounced for mid-elevation forests in the northern Rocky Mountains.
The new finding points to climate change, not fire suppression policies and forest fuel accumulation, as the primary driver of recent increases in large forest fires.
"I see this as one of the first big indicators of climate change impacts in the continental United States," said research team member Thomas W. Swetnam, director of the Laboratory of Tree-Ring Research at The University of Arizona in Tucson.
"We're showing warming and earlier springs tying in with large forest fire frequencies. Lots of people think climate change and the ecological responses are 50 to 100 years away. But it's not 50 to 100 years away -- it's happening now in forest ecosystems through fire."
The researchers found the wildfire season is now starting earlier, fires are lasting longer and the fire season is ending later.
"The length of the fire season has increased almost two-and-one-half months compared with 1970 to 1986," Swetnam said. "That's a remarkable thing in itself."
In recent years, wildfires in the western United States have burned hundreds of homes annually and caused extreme and sometimes irreversible damage to natural resources. Fire-figh
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Contact: Mari N. Jensen
mnjensen@email.arizona.edu
520-626-9635
University of Arizona
6-Jul-2006