Intense and deeply destructive "super fires," like Colorado's current Waldo Canyon fire, which has claimed two lives and burned 350 homes, are almost assured in Northern California's future, according to a U.S. Forest Service scientist.
"Typically we're seeing an earlier fire season and that fire season is lasting longer," said Malcolm North, plant ecologist with the Pacific Southwest Research Station of the U.S. Forest Service. North works out of the station's Davis office.
The culprits, said North, are weather fluctuations and climate change. He said the warmer temperatures and drier winters seen recently in the region are creating ideal conditions for intense and hard-to-control fires like the Colorado fire.
"What we're seeing now is that snow reserves are less in the Sierras and runoff is happening earlier in the year," he said.
That creates drier conditions in areas where fires burn hottest the forests. The most difficult to deal with are "crown fires," whose flames travel from one tree to another, usually at high speed. It is common for crown fires to move at 30 mph, North said.
"Data show that since the 1980s there has been an increase in both the size of fires and acreage of burn, and particularly the burn severity," he said. "We now know from research that high severity fires, such as crown fires, generally made up 10 to 15 percent of the area of a forest fire. Currently, the average is more like 30 to 35 percent."
He said drier conditions at lower elevations, such as grasslands, will also lead to more fires, which are vexing because they move fast and burn closer to homes and buildings. These fires will also be earlier in the season. Typically, it only takes two weeks after the last rain for grassland plants to dry out and become fire-prone, North said.
"We live in a Mediterranean climate, so plants here are adapted to three to four months of drought yearly, but what appears to be happening now is that we're getting droughts lasting more like five to six months," he said.
This year has already proved an active fire season. In El Dorado County, from Jan. 1 to June 29 of this year, 76 fires burned more than 140 acres. Last year saw 48 fires and 44 acres burned in approximately the same time frame, according to data from the California Department of Forestry and Fire Protection.
The largest fire years since 1950 have all occurred since 2000, according to a recent U.S. Forest Service report on California wildfires. The annual average of acres burned since 2000 is twice the average for fires that happened between 1950 and 2000.
One of the major concerns is that a "super fire" like the 2007 South Lake Tahoe Angora fire will happen again. That fire scorched more than 3,000 acres and destroyed 254 homes.
"In Lake Tahoe we're seeing conditions that are similar to what we had in 2007 with the Angora fire," said Beth Brady, fire prevention officer with the U.S. Forest Service at Lake Tahoe.
"It's not unexpected because we had such a light winter this year, which means vegetation and fuels on the forest floor are drying out. We're getting down to some pretty low moisture levels, which means vegetation is available to burn early," she said.
So far the Forest Service has not seen an increase in lightning fires this year the most common origin of wildland fires in Northern California. Typically, about 10 percent to 15 percent of fires in the area are started by humans, with the Angora fire a devastating example.
"The concern is what we're going to get for human ignition and human carelessness," Brady said. "Thankfully, so far, we're about a normal level for that."
In the time she has been working for the Forest Service, Brady has noticed a clear trend of longer fire seasons.
"We certainly have a year-round fire season now. When I started 18 years ago the season was pretty much confined to late July through early October. This past year we had fires in December, January and February, and that's highly unusual for us," she said.
North said that despite fluctuations from year to year, long fire seasons and high potential for devastating fires are here to stay.
"Fire is an inherent part of the system. You can never exclude it. You can suppress it and keep it from happening for a while, but eventually all of these systems will burn. Every homeowner and policymaker needs to know that," he said.