Proposed Fire Hazard Severity Zones in the Local Responsibility Areas in the Town of Ross, San Anselmo and Fairfax

The Ross Valley Fire Department, Joint Powers Authority (JPA), in partnership with the Sleepy Hollow Fire Protection District and the Towns of Fairfax, San Anselmo and Ross encourages all residents within Local Responsibility Areas (LRA) of the Ross Valley Fire Department to review and submit public comment.

The Office of the State Fire Marshal (OSFM) is required to classify lands within State Responsibility Areas (SRA) into Fire Hazard Severity Zones (FHSZ) of Moderate, High, and Very High fire hazard severity based on consistent statewide criteria and based on the severity of fire hazard that is expected to prevail in those areas. In April of 2024, the FHSZ map for the state of California was adopted for the SRA.

After the devastating Oakland Hills fire of 1991, Assembly Bill 337 was passed and calls for the California Department of Forestry and Fire Protection (CAL FIRE) to evaluate fire hazard severity in the LRA as well. Both the OSFM and CAL FIRE have now classified, evaluated, and recommended FHSZ in the LRA and released updated maps on February 24, 2025 and now invite the public to submit comments to their own jurisdictions.

The maps can be viewed in person at all local planning departments and/or viewed online at Rossvalleyfire.org then follow the link for Local Responsibility Area Fire Hazard Severity Zone Update and select your jurisdiction (Town of Fairfax, Town of San Anselmo or Town of Ross).

Questions and comments about the LRA maps can be directed to:

• Ross Valley Fire Department: 777 San Anselmo Ave, San Anselmo. Email comments that apply within Ross Valley Fire jurisdictional boundaries to: prevention@rossvalleyfire.org or call Robert Bastianon, Sr. Fire Inspector at (415) 258-4673

For more information on the maps, visit: https://osfm.fire.ca.gov/what-we-do/community-wildfire-preparedness-and-mitigation/fire-hazard-severity-zones

BACKGROUND INFORMATION FROM CAL FIRE

Each zone includes relatively homogeneous lands and classifications are based on fuel loading, slope, fire weather, and other relevant factors present, including areas where winds have been identified by the department as a major cause of wildfire spread.

The maps evaluate “Hazard,” not “Risk.” Hazard is based on physical conditions that create expected fire behavior over a 50-year period without considering risk (the short-term modifications such as creating defensible space, fuel breaks, fuel reduction projects, and ignition resistant building construction). The map is like flood zone maps, where lands are described in terms of the probability level of a particular area being inundated by floodwaters, and not specifically prescriptive of impacts.

Fire Hazard Severity Zones are found in areas where the state has financial responsibility for wildfire protection and prevention, called the State Responsibility Area (SRA). More than 31 million acres are in this area. Under Senate Bill 63 (Stern, 2021) Government Code 51178 was amended to also identify the Moderate, High, and Very High Fire Hazard Severity Zones in Local Responsibility Areas (LRA) which are protected by our local Fire Protection Districts.

The zones are used for several purposes including to designate areas where California’s defensible space standards and wildland urban interface building codes are required. They can be a factor in real estate disclosure, and local governments may consider them in their general plan.

Insurance companies use risk models, which differ from hazard models, because they consider the susceptibility of a structure to damage from fire and other short-term factors that are not included in hazard modeling. It is unlikely that insurance risk models would utilize CAL FIRE’s Fire Hazard Severity Zones as a factor, but much of the same data that is used in the Fire Hazard Severity Zone model are likely included in the insurance companies’ risk models. However, insurance risk models incorporate many additional factors and that change more frequently than those that CAL FIRE includes in its hazard mapping, which is built to remain steady for the next 10+ years.

The maps were last updated in 2024 when CAL FIRE updated the FHSZs for the entire State Responsibility Area (SRA). Between 2008- 2011 the department worked with local governments to make recommendations of the Very High Fire Hazard Severity Zones within Local Responsibility Area (LRA). This will be the first update to the LRA maps since they were developed.

The California Public Utilities Commission (CPUC) sponsored map, known as "CPUC High Fire Threat District Map” (HFTD), includes similar factors as those in the FHSZ maps, however the CPUC HFTD Map is designed specifically for identifying areas where there is an increased risk for utility-associated wildfires. As such, the CPUC map includes fire hazards associated with historical powerline-caused wildfires, current fuel conditions, and scores areas based on where fires start, as opposed to where potential fires may cause impacts.

What is new for this update is the incorporation of climate data. A 2-kilometer grid of climate data covering the years 2003-2018 has been used in this update. The previous model used stock weather inputs across the state to calculate wildland fire intensity scores. The updated model will adjust fire intensity scores based on the most extreme fire weather at a given location considering temperature, humidity, and wind speed. In addition, ember transport has been modeled based on local distributions of observed wind speed and direction values instead of using a generic buffer distance for urban areas adjacent to wildlands.

This updated modeling also places an emphasis on the spread of embers. Embers spread wildfire because they can travel long distances in the wind and ignite vegetation, roofs, attics (by getting into vents), and decks.