By Mark Grossi
Fresno Bee (California)
Copyright 2006 McClatchy Newspapers, Inc.
All Rights Reserved
A landmark study led by a future University of California at Merced professor concludes that global warming is driving an ominous expansion of wildfires in the Sierra Nevada and the West.
Over the past three decades, the warming has brought earlier springs, drier high-country forests and far more destructive fires, said Anthony Westerling, a researcher at Scripps Institution of Oceanography. This fall, Westerling will become a professor of environmental science and analysis at UC Merced.
Westerling and his colleagues said the warming climate is the most important reason for wildfire expansion, calling it even more influential than past management practices that allowed the forests to become overgrown and more vulnerable to fire.
The researchers found wildfires are burning more than six times the acreage they did in the 1970s, and the dramatic expansion can be traced to the mid-1980s, when global temperatures rose. Last year, a record-setting 8.6 million acres burned throughout the country.
“The forests are already thick and ready to burn,” Westerling said. “They become more sensitive to dry conditions. The greatest increase in fire frequency was in the northern Rockies, but the Sierra Nevada, southern Cascades and other places have been affected, too.”
Right now, two large wildfires are raging in California. A 26,000-acre fire in San Bernardino County is being fueled by parched terrain and brisk desert winds. And a 17-square-mile fire in western Stanislaus County is threatening a dozen homes.
Until now, no one has closely studied fire statistics, temperature records, stream flows and other data to tease out the effects of climate on forest fires. The new study covered more than 1,100 large wildfires between 1970 and 2003.
The research, published online on the Web site of the journal Science, included work from other researchers at Scripps and the University of Arizona. The National Oceanic and Atmospheric Administration, the Department of Energy and the U.S. Forest Service provided grants for the study, according to Scripps.
The conclusions in the research make sense, said Tom Wordell, wildland fire analyst with the National Interagency Fire Center in Boise, Idaho. He has been involved in firefighting and fire analysis for more than 30 years.
“Just about 1986, things got a lot more active,” he said. “The research concerns me. It implies the cards are stacked against us.”
Federal officials said wildfire has not yet been widespread in the Sierra this year because late spring storms left the forests wet.
But it only takes two weeks of dry weather and warm wind to prime a forest for a fire, said private forester John Mount, who manages the Southern California Edison Co. forest east of Fresno.
“Right now, I don’t think we could get a big fire going,” he said. But that “could change quickly.”
There have been many large Sierra fires in Central California, including the intense complex of fires that briefly closed Yosemite Valley in 1990 and burned 15,000 acres.
More recently, the immense McNally fire torched more than 150,000 acres in the Sequoia National Forest over five weeks in 2002.
Overgrowth in the Sequoia forest — and many other places in the Sierra’s 11.5 million acres of federal forest — is blamed for helping fires burn longer. The overgrowth occurred largely because federal officials had a policy to douse every fire for most of the last century.
That effort stopped many beneficial, slow-moving fires that eliminate brush and open places for larger trees to grow. Such fires — along with some tree cutting — are now used to thin the forests.
Thinning efforts have been mired in arguments and lawsuits over how the job should be done to protect nature. Meanwhile, big fires continue each year.
“Fires are getting bigger and hotter” in the Sierra, said spokesman Matt Mathes of the U.S. Forest Service. “We can do a great deal to reduce fuels in the forest, but we can’t do anything about climate warming. We’re anxious to see this study.”
Westerling said forest thinning should continue throughout the West. But the warming climate will be the biggest influence on fire seasons in the future.
“We can expect more years of frequent fires,” he said.
The springs and summers from 1987 to 2003 were the warmest since record-keeping started in 1895, the study showed.
The fire season has expanded by almost 80 days, and the average time from discovering a large wildfire to controlling it has stretched from about a week to more than five weeks.
One of the researchers, Scripps climatologist Dan Cayan, said the warming over the past two decades is beyond the variation seen historically.
The study did not enter the debate over people creating greenhouse gases and contributing to global warming.
But Cayan said the human contribution of such gases, such as carbon dioxide from fuel combustion, could be a key.
“What we’re seeing is alarming because climate change is surely going to warm the West over the next century,” Cayan said.