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Friday, July 7, 2006 - Page updated at 12:00 AM

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Western wildfires linked to climate change

A broad change in the West's climate — spring coming earlier, mountain snows melting sooner and forests turned to tinder by rising temperatures — has stoked an increase in large wildfires over the past 34 years, scientists reported Thursday.

More than land-use changes or forest-management practices, the researchers concluded, the changing climate was the most important factor driving a four-fold increase in the average number of large wildfires in the western United States since 1970.

All told, the average fire season has grown more than two months longer, while fires have become more frequent and harder to extinguish. They also burn longer and destroy 6.5 times more land than in the 1970s, the researchers found.

Last year was the worst wildfire season on record, with more than 8.53 million acres burned nationwide by the end of December.

So far this year, more than 60,000 wildfires have charred almost 3.9 million acres — twice the number of fires during the same period last year, according to the National Interagency Fire Center in Boise, Idaho.

"It all fits together," said climate researcher Anthony Westerling, who led the research while at the Scripps Institution of Oceanography in La Jolla, Calif. "The [fire] seasons do start earlier and run longer. It is consistent with a changing climate."

In the first detailed study of its kind, scientists at Scripps and the University of Arizona analyzed 34 years of wildfire activity, temperature records, snow-melt trends, stream flows and other climate-related data.

Researchers said, for instance, that an earlier snowmelt can lead to an earlier and longer dry season, which provides greater opportunities for large fires.

The research, published online Thursday by the journal Science, was funded by grants from the National Oceanic and Atmospheric Administration, the U.S. Forest Service and the California Energy Commission.

The scientists found that climate change magnified a regional pattern of natural disaster that every year costs more than $1 billion in federal firefighting expenses and untold property damage.

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"I think this is the equivalent for the West of what hurricanes are [elsewhere in the country]," said fire ecologist Steven Running at the University of Montana in Missoula, who was not connected with the research. "This is an illustration of a natural disaster that is accelerating in intensity as a result, I feel, of global warming."

Outlook for Northwest

Fire officials are largely expecting a typical fire season in the Northwest but with at least one unusual hotspot: Western Washington.

On the damp side of the Cascades, wildfires are rare, and a true conflagration comes around only once every few hundred years. But several weeks of hot, dry weather have increased the chances for fire west of the mountain passes.

"Fire is ruled by long-term drought and short-term drought, and Western Washington is under the influence of short-term drought," said John Saltenberger, fire weather program manager for the Pacific Northwest Wildfire Coordinating Group.

It will take more than just a few cool days and some rain to change that dynamic, he said. But, he added, large fires also require a spark and the right weather pattern to sustain them, and the season is still young.

Meanwhile, the Okanogan Valley, which in recent years has been the most fire-prone area of the Northwest, is again at risk for fire, along with southern Oregon, where heavy grass crops are drying out just as weather officials are expecting lots of lightning.

The Scripps research team stopped short of linking global warming due to rising levels of greenhouse gases to the increasing wildfire intensity, but they were confident that they have documented a broad climate trend at work and not a fluke of natural weather variability.

"I see this as one of the first big indicators of climate-change impacts in the continental United States," said Thomas Swetnam, an expert on fire history and director of the laboratory of tree-ring research at the University of Arizona in Tucson. Swetnam was part of the research team.

The researchers studied more than 1,100 large wildfires between 1970 and 2003.

Average spring and summer temperatures in the West were more than 1.5 degrees higher between 1987 and 2003 than during the previous 17 years.

The researchers reported that almost seven times more forested federal land burned between 1987 and 2003 than during the previous 17 years. During the same period, the length of the wildfire season increased by 78 days. The average time between when a fire was discovered and when it could be extinguished also lengthened — from 7.8 days to 37.1 days.

Higher in the Rockies

The impact of rising temperatures on wildfires seemed most profound in the northern Rockies, which accounted for 60 percent of the blazes from 1987 to 2003, and least pronounced in arid Southern California.

In recent years, federal forestry managers have attempted to rectify the effects of previous generations of fire suppression, which allowed combustible vegetation to build up to dangerous levels, by thinning forests and logging weak trees.

"The most stark conclusion here is that, while they do say land use and management has played an important role, the broad-scale increase in wildfire frequency has been driven primarily by recent changes in climate," said wild-land fire analyst Tom Wordell at the National Interagency Fire Center. "It does not paint a pretty picture for future fire activity, given the climate model predictions."

The Government Accounting Office recently reported that the cost and severity of fires has grown as more people build homes on the edge of national forests and other federal lands.

If regional temperatures continue to rise, as many computer climate models predict, wildfire activity throughout the West will intensify so long as there is acreage to burn, several experts said.

Moreover, as more forests burn, the destruction will release massive amounts of carbon dioxide, further accelerating the increase of greenhouse gases in the atmosphere and helping to further increase temperatures.

Seattle Times staff reporter Craig Welch contributed to this report, which also includes information from The Associated Press.

Copyright © 2006 The Seattle Times Company

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