Dire forecast for fire season in the West The West

DUBLIN, CA - JUNE 24: Firefighters from San Francisco, California use hand tools to make a fire break during a multi-agency wildfire training drill June 24, 2009 in Dublin, California. Fire departments from several San Francisco Bay Area counties participated in a live-fire wildfire drill as fire crews gear up for what is expected to be a busy summer as California continues to experience a drought. (Photo by Justin Sullivan/Getty Images) less DUBLIN, CA - JUNE 24: Firefighters from San Francisco, California use hand tools to make a fire break during a multi-agency wildfire training drill June 24, 2009 in Dublin, California. Fire departments from ... more Photo: Justin Sullivan, Getty Images Photo: Justin Sullivan, Getty Images Image 1 of / 7 Caption Close Dire forecast for fire season in the West 1 / 7 Back to Gallery

This fire season throughout California and the West is likely to be one of the worst on record as heat and drought persist through the fall, scientists monitoring the state's vegetation predict.

The new forecast from U.S. Forest Service researchers is based on a survey of forests, underbrush, grasslands and farm fields throughout the region, including the Sierra Nevada, coupled with current climate models and long-term weather studies.

Much of the state - particularly the Central Valley, the Bay Area and the region north of Los Angeles - will remain "extremely dry," the worst possible fire condition, or "severely dry," through December, said Ronald Neilson, a Forest Service researcher and botany professor at Oregon State University.

Neilson, who studies the links between climate and vegetation, heads the group that has been updating its wildfire forecasts every month for more than 10 years.

"The forecasts have been almost surgically accurate," Neilson said this week, "but they don't know about lightning or people with matches."

The vast majority of wildfires are caused by human activity, sparked by careless campers, arsonists or people inappropriately using equipment in dry areas, according to the state Department of Forestry and Fire Protection. Lightning causes roughly 5 percent of the wildfires in the agency's jurisdiction, while 12 percent are caused by arson and 30 percent by improper use of mechanical equipment, Cal Fire records show.

So far this year, California's largest blaze hit Santa Barbara County in early May. The Jesusita fire burned more than 8,700 acres and destroyed about 80 homes. There have been few large, destructive fires in Northern California so far.

Neilson's regular reports are "very helpful" to the state, said Del Walters, director of Cal Fire. "We use that kind of data to follow changing vegetation patterns and climate trends closely all the time."

Neilson's fire forecasts are based primarily on an area's flammability as water in the ground dries and forests, crops and grasslands turn tinder-dry.

Fire hazards in California and the Pacific Northwest have been increasing year after year for more than 30 years, Nielson said, because of what he called "an incredibly rapid rate of climate warming."

Beyond California, Neilson's current forecast shows the worst drought conditions persisting in western Oregon and Washington, as well as in pockets of North Carolina and Northern Wisconsin. For much of the northern Midwest and Northeast, however, the forecast for the rest of the year calls for "very wet" or "extremely wet" conditions.