California wildfires start in the woods. Why do cities keep burning?

The Camp Fire – the state’s most destructive and deadliest – began Thursday in a wild and wooded part of unincorporated Butte County before demolishing the Northern California town of Paradise, leaving at least 88 people dead and most of the town’s homes burned to cinders.

It was a rural fire that turned into an urban nightmare — an increasingly common occurrence in California.

Paradise, with 26,682 people, is Butte County’s second-largest city after Chico, which was also threatened by the Camp Fire. It’s California’s latest city to be attacked by flames after the Tubbs Fire tore through Santa Rosa last October and the Carr Fire destroyed nearly 1,000 homes around Redding in August.

Farther south, the Woolsey Fire endangered thousands of homes from Calabasas and Thousand Oaks to Malibu.

Climate change contributes to the growing destruction from California wildfires. Hot, dry weather conditions that help carry fires for thousands of acres are often present nearly year-round now. The state’s urban sprawl and encroachment into formerly undeveloped land is the real catalyst, though, said former Sacramento Metropolitan Fire District chief Kurt Henke.

A recent Villanova University study found there are about 7 million homes in fire-prone areas in the West, more than 10 times the 600,000 or so that were present in 1940. That includes nearly 2,000 homes in Folsom and about 4,600 in the greater Sacramento region. Environmental scientists believe 1.2 million more could be built in the highest-risk areas statewide between 2000 and 2050.

The same bucolic landscape that earned Paradise its name can magnify the effects of natural disasters, Cal Fire spokesman Rick Carhart said. Paradise is built atop a ridge, with canyons descending on either side. Carhart said fires that reach the bottom of canyons have every intention of climbing back to the top. Those kinds of geographic features are present in many foothill towns, where development continues to push dense housing deeper into rural areas.

The infrastructure necessary for housing also brings dangers. Overhead power lines have been cited or suspected as the cause of some of California’s most deadly wildfires, prompting PG&E to try pre-emptive outages when high winds kick in. At this point, Henke said, house hunters should view future blazes as inevitable when buying in places such as the Sierra Nevada foothills and Central Valley.

“In these places, it’s not if a fire is going to happen, it’s when it’s going to happen,” said Henke, who now consults with fire departments. “We’re basically building structures right in the path of firestorms. There’s just some places a subdivison shouldn’t be built.”

Fire experts use the term wildlife urban interface, or WUI, to refer to the area where human building meets or intermingles with undeveloped natural land. California’s WUI zone grew 20 percent from 1990 to 2010, according to U.S. Forest Service data.

Paved streets have replaced underbrush, but most developments on natural land keep some native trees and other vegetation intact, said Keith Gilless, dean emeritus and a current professor of forest economics in UC Berkeley’s College of Natural Resources.

When fires get large enough that they “crown” — spread from treetop to treetop — they’ll move nearly as quickly in a vegetation-rich residential neighborhood as they would in the woods, Gilless said.

“We have a lot of people living in ‘urban forest’ conditions,” Gilless said. “It’s sort of a mixed bag. If you have a forest canopy and put homes under it and roads under it, that can help (limit the fire) ... but in an extreme fire, homes become fuel themselves.”

Camp Fire in Butte County

Red circles on this live-updating map are actively burning areas, as detected by satellite. Orange circles have burned in the past 12 to 24 hours, and yellow circles have burned within the past 48 hours. Yellow areas represent the fire perimeter.
Source: National Interagency Fire Center

State officials have taken steps to limit people’s exposure to wildfires in recent years.

Cal Fire requires new developments near wilderness areas to be built out of fire-resistant materials and requires owners to keep easily combustible vegetation at least 100 feet from walls. The state budget funded “pre-positioning,” or mobilizing strike teams to vulnerable locations before a wildfire ignites, for the first time in 2018.

Pre-positioning gets difficult, though, when multiple parts of the state are under threat of simultaneous ignition. The California Office of Emergency Services sent preemptive strike teams to 10 counties earlier this week. Five were in the Bay Area, four were in greater Los Angeles and the other was in Lake County.

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Even if OES strike teams had pre-positioned in Butte County, Carhart said he didn’t think it would have made much difference because the Camp Fire started as a 10-acre blaze in an extremely remote area and quickly spread via high winds and heavy fuel. Even if firefighters made an unlikely early push to tamp down the blaze, Carhart said, the fire was always going to be difficult to control.

“We would love to be able to get every single resource we need every single time we have a fire. It doesn’t always happen that way just because of other things going on throughout the state,” Carhart said. “This could be one of those situations where it didn’t really matter what was on hand.”

This story has been updated on Nov. 25 to reflect a correction in the death toll of the Camp Fire. Authorities earlier erroneously reported the number of fatalities as 87. The correct number as of Nov. 25 is 85.

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