Several Bay Area cities have seen striking increases in areas deemed at high and very high risk of wildfire, new maps issued by state fire officials show.
Cal Fire’s Fire Hazard Severity maps for local jurisdictions, issued in 2011, are being updated, with Bay Area maps released Monday. While the old maps showed only areas deemed “very high” hazard, the new ones show that category, with “high” and “moderate” below it.
Homeowners who live in areas now deemed at very high hazard on the maps will have to comply with “Zone 0” regulations expected to take effect at the start of next year that include a mandated five-foot zone around every house free of flammable materials vulnerable to flying embers.
San Jose, deemed to have 3,310 acres of very high hazard in 2011, saw the acreage in that category more than double to 7,142, with another 15,767 acres classified as high hazard, and 5,494 moderate.
“It’s an improved science method that we’re using,” Kara Garrett, a deputy state fire marshal, said Monday. “There are a lot of nuances in different areas. We’re getting a better view.”
Cupertino, with only 16 acres in the very high hazard zone in 2011, now has 1,053 acres in that category, another 542 considered high hazard, and 406 moderate.
Morgan Hill lost area considered very high hazard — the acreage dropped to 638 in current maps from 1,506 in 2011 — but has 1,493 acres deemed high hazard, and 950 moderate.
In the East Bay, Orinda saw a dramatic increase in fire hazard. After having 2,424 acres deemed very high hazard in 2011, it now has 5,241 acres in that classification, with another 803 acres of high danger and 928 moderate.
Oakland, however, saw a large drop in the size of the area considered at risk. In 2011, the city had 10,838 acres considered very high hazard, but that number dropped to 1,945 in the latest map, with another 2,598 deemed high hazard and 2,553 moderate.
To determine the hazard level for an area, factors such as fire history, existing and potential vegetation, predicted flame length and ember-dispersion distances, terrain and weather patterns are included, according to Cal Fire.
Fire officials emphasize that the maps are intended to show hazard, not risk, like flood-zone maps that show the probability an area will be submerged, rather than the effects of submersion. The hazard assessment is based on “the physical conditions that create a likelihood and expected fire behavior over a 30 to 50-year period without considering mitigation measures such as home hardening, recent wildfire, or fuel reduction efforts,” Cal Fire said.
Kimberly Giuliacci, division chief at the Woodside Fire Protection District, worries the maps could give residents in areas considered moderate or high hazard a false sense of security.
“The fire isn’t going to stop because you’re in a moderate zone,” Giuliacci said, adding that she would like to see Zone 0 regulations apply to all the hazard zones.
Also, Giuliacci said, the maps do not consider structures including homes and other buildings as “fuel” that can contribute to rapid fire spread, as happened in the catastrophic Los Angeles fires.
“We’ve got ADUs. We’ve got detached garages. We’ve got barns,” Giuliacci said. “That’s a big fuel load in itself.”
Cal Fire will continue to update the maps to include feedback from local jurisdictions, who have the option of pushing acres into higher hazard categories, but not lower, Garrett said. Local officials can use the maps for fire prevention, preparing fire responses, and determining which state building codes apply in particular areas, Garrett said.
Wildfire experts in recent years have highlighted the danger of wind-blown embers that can float long distances and ignite flammable materials on and around homes. With climate change helping bring larger, more frequent wildfires, state authorities have focused heavily on pushing residents to create “defensible space” around homes.
For homeowners in very high hazard areas, complying with the Zone 0 regulations will come at varying costs, said Seth Schalet, CEO of the non-profit Santa Clara County FireSafe Council.
“That’s going to be the ultimate challenge,” Schalet said. “How do people pay for this?”