Global Warming Linked to Increase in Western U.S. Wildfires

SAN BERNARDINO, California, July 12, 2006 (ENS) - A runaway wildfire has destroyed several homes, and at least 1,500 residences and an equal number of other structures are threatened today in the central California areas of Pioneertown, Flamingo Heights, and Rim Rock. Evacuations are ongoing, and an evacuation Center has been set up at the Yucca Valley Community Center.

Some 2,500 firefighters are battling the 6,000 acre blaze, but high winds and steep, inaccessible terrain are impeding containment efforts, and fire officials report extreme fire behavior. Four people have been injured, including two firefighters.

Known as the Sawtooth Complex, the fire was started by lightening on Sunday just north of the northwest corner of Joshua Tree National Park in the San Bernardino Unit of the California Department of Forestry and Fire Protection. It is threatening Pioneertown where many old-time Western movies were filmed by stars such as Gene Autry and Roy Rogers.

Firefighters could not say when they might have the blaze under control. California Department of Forestry Capt. Marc DeRosier said, "If we have more of the same with the high winds and high temperatures it could be trouble."

Eight new large fires were reported across the United States today, four in the Eastern Great Basin and one each in the Southern California, the Western Great Basin, the Northern Rockies, and southern areas. Very high to extreme fire indices were reported in Arizona, Alaska, California, Montana, Nebraska, Nevada, New Mexico, North Dakota, Oregon, south Dakota, Utah and Wyoming.

Western wildfires have attracted broad public and political attention in recent years due to the severity and expanse of the areas they have consumed, hundreds of homes burned and devastating damage to natural resources.

Fire-fighting expenditures for wildfires now regularly exceed one billion dollars per year.


Firefighters battle more intense and longer lasting fires than they did 30 years ago. (Photo courtesy House Resources Committee)
Global warming is partly responsible for an increase in numbers of large wildfires across the Western United States since the late 1980s, according to new research by scientists with the Scripps Institution of Oceanography and the University of Arizona.

Large wildfire activity increased "suddenly and dramatically" in the late 1980s with longer wildfire seasons and an increased number and more potent wildfires, partly because of global warming, the new statistical study reveals.

The new findings, published in the current issue of the journal "Science," point to climate change, not fire suppression policies and forest accumulation, as the primary driver of recent increases in large forest fires. Researchers linked rising seasonal temperatures and the earlier arrival of spring conditions with the increase in wildfire activity.

"The increase in large wildfires appears to be another part of a chain of reactions to climate warming," said Dan Cayan, a coauthor of the paper and director of Scripps' Climate Research Division.

"The recent ramp-up is likely, in part, caused by natural fluctuations, but evidence is mounting that anthropogenic effects have been contributing to warmer winters and springs in recent decades," he said.

In the most systematic analysis to date of recent changes in forest fire activity, Cayan, together with Anthony Westerling and Hugo Hidalgo of Scripps and Tom Swetnam of the University of Arizona, compiled a database of large western wildfires since 1970 and compared it with climate and land surface data from the region.


From left, Anthony Westerling and Dan Cayan. Using statistical methods developed in climate forecasting research, these scientists at Scripps Institution of Oceanography at the University of California, San Diego, developed the most complete analysis to date of wildfire activity and climate warming. (Photo courtesy UCSD)
They compiled a comprehensive time series of 1,166 forest wildfires of at least 1,000 acres that had occurred between 1970 and 2003 from wildfire data covering western U.S. Forest Service and National Park Service lands.

To investigate what role climate might play, the scientists compared the time series, the timing of snowmelt and spring and summer temperatures for the same 34 years.

For the timing of peak snowmelt in the mountains for each year, they used the streamflow gauge records from 240 stations throughout western North America.

The team also used other climatic data such as moisture deficit, an indicator of dryness.

The results show a marked increase in large wildfires in western U.S. forests beginning around 1987, when the region shifted from predominantly infrequent large wildfires of short duration - average of one week - to more frequent and longer-burning wildfires that last an average of five weeks.

"I see this as one of the first big indicators of climate change impacts in the continental United States," said Swetnam, who serves as director of the Laboratory of Tree-Ring Research at The University of Arizona in Tucson.


Thomas Swetnam is director of the Laboratory of Tree-Ring Research (LTRR) at The University of Arizona in Tucson. (Photo courtesy LTRR)
The scientists found a jump of four times the average number of wildfires beginning in the mid-1980s compared with the 1970s and early 1980s. The comparison showed that the total area burned was six and a half times greater.

Also in the mid-1980s, the length of the yearly wildfire season, March through August, extended by 78 days, a 64 percent rise when comparing 1970-1986 with 1987-2003.

"We're showing warming and earlier springs tying in with large forest fire frequencies," Swetnam said. "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 authors conclude that the increased frequency of large and devastating wildfires may change forest composition and reduce tree densities, transforming the role of western U.S. forests as a storage "sink" for sequestering some 20 to 40 percent of all U.S. carbon to a source for increasing carbon dioxide in the atmosphere.

The research was supported by the National Oceanic and Atmospheric Administration's Office of Global Programs, the National Fire Plan via the United States Forest Service's Southern Research Station, and the California Energy Commission.