"There is a very dramatic increase in forest fires in the West" over the past 15 years, said Anthony Westerling, a researcher with the Scripps Institute of Oceanography, La Jolla, Calif.

The data show four times more large forest wildfires, at least 1,000 acres, from 1986 to 2003 than in the period from 1970 to 1986. The earlier period covered 238 fires, and 1,788,536 burned acres, while the latter had 928 blazes, and 11,969,810 burned acres.

Westerling and other researchers report in this week's edition of the journal Science that dry winters and warmer weather seem to be linked to the jump in the number of forest wildfires. While climate change may play a role in this pattern, natural variation in weather patterns from year to year could also take partial blame.

"It is probably some of both," said Dan Cayan, another Scripps researcher involved in the study.

Places like Yellowstone National Park have endured higher-profile fires - most recently the 2003 blaze near the east entrance that scorched 18,000 acres - but Utah forests occasionally burn as well. One of the last major forest fires to tear through northern Utah was the 2002 East Fork Fire, which burned 14,000 acres in the Uinta Mountains.

The Science study examined forest fires that hit large stands of trees, such as Douglas fir and Ponderosa pine. Most of the increase in fires took place between elevations of 5,500 and 8,800 feet. The analysis doesn't include many of the most recent wildfires in Utah, which affected scrub and brush.

While Utah's big-tree forests don't burn too often, the research could serve as a warning, said Beth Corbin, a fire ecologist for Uinta and Wasatch-Cache national forests.

"Over the long haul, it could be cause for concern," Corbin said.

Utah, like other parts of the West, relies on snowpacks for its summer water supply. The snowpack also has benefits for keeping forests moist. If the snow melts sooner, the soil dries earlier and vegetation becomes drier. This chain of events creates trees that are ready to burn, Cayan said.

Researchers at Scripps, the University of California, Merced, the U.S. Geological Survey and the University of Arizona, Tucson, examined weather and fire records over the past 30 years for the western United States.

If the weather patterns continue, many fires may burn longer and firefighters, even with increases in resources, may have to let some burn out on their own, Westerling said.

"You're not going to reverse this trend with fire suppression," he said.

Ron Masters, director of the Tall Timbers Fire Ecology Research Station in Florida, said "prescribed fire is our best insurance against severe wildfire."

"Natural and prescribed fires play a vital role in restoring and maintaining forest and grassland ecosystems," he said in a statement.

Most of the increase in larger forest wildfires takes place in the northern Rockies, with fewer such occurrences in the Southwest. Westerling said this may mean fire management policies would have to be different for the various areas of the West.

Due to the short period of the study time, it is difficult to say how much of a role global warming has played, but climate change models predict an increase in the number of forest fires in areas of warming temperatures and earlier springs.

"Climate change model projections indicate that a moderate to substantial amount of warming is in our future," Cayan said of the West.

Said Louisa Evers, a fire ecologist expert, in a statement, "The science justifies action now to change land management direction and practices to mitigate the effects of ongoing climate change."

glavine@sltrib.com