City Council
Staff Report
From: City Manager
Report Type: CONSENT CALENDAR
Lead Department: Fire
Meeting Date: June 9, 2025
Report #:2504-4596
TITLE
FIRST READING: Adoption of an Ordinance amending Section 15.04.410 (Definition of Wildland- Urban Interface Fire Area) to adopt and incorporate the 2025 CAL FIRE Fire Hazard Severity Zone (FHSZ) Map for the City of Palo Alto. CEQA status: Not a Project.
RECOMMENDATION
Staff recommends that the City Council adopt Exhibit the CAL FIRE Fire Hazard Severity Zone (FHSZ) map, as recommended by the California Department of Forestry and Fire Protection (CAL FIRE), for areas within the City of Palo Alto's jurisdiction.
EXECUTIVE SUMMARY
CAL FIRE is mandated by state law to identify and map areas with significant fire hazards, and periodically revise and update its designation of zones. These maps, known as Fire Hazard Severity Zone (FHSZ) maps, categorize areas based on factors that influence fire likelihood and behavior. Updates in state law since 2021 now require that a local agency, including the City of Palo Alto, designate by ordinance the moderate, high, and very high FHSZs in its jurisdiction within 120 days of receiving recommendations from the State Fire Marshal. (Gov. Code 51179(a)).
Recent updates to the state’s FHSZ maps were issued for the Bay Area, including Palo Alto, February 24, 2025.The City has provided opportunities for public review and comment on the CAL FIRE FHSZ map March 26 through April 30, 2025, and adoption of the CAL FIRE FHSZ map is a necessary next step to protect the City of Palo Alto from the increasing threat of wildfires. It ensures compliance with state law, enhances public safety, and promotes responsible land-use planning. Staff recommends that the City Council adopt the map as presented. Under state law, a local agency has discretion to add areas not identified by the State Fire Marshal or increase the fire hazard severity identified by the state, but not to remove areas or reduce the hazard severity level (Gov. Code 51179(b)).
BACKGROUND
The State Fire Marshal is required to classify lands within State Responsibility Areas (SRA) into fire hazard severity zones. In 1992, Assembly Bill 337 required CAL FIRE to evaluate fire hazard severity in local responsibility areas and make a recommendation to the local jurisdictions where Very High FHSZ exists. Under Senate Bill 63 (Stern, 2021) Government Code 51178 was amended to also identify the Moderate and High Fire Hazard Severity Zones with the Very High in Local Responsibility Areas (LRA). Each zone must encompass relatively homogeneous lands and be based on fuel loading, slope, fire weather, and other relevant factors, including areas where winds have been identified as a major cause of wildfire spread.
The FHSZ maps are essential tools for the following:
•Wildfire Preparedness: They provide critical information for residents, property owners, and the City to understand the level of fire hazard in specific areas. •Building Codes: The maps inform building code requirements, particularly for new construction and renovations, to enhance structural resistance to wildfire. •Defensible Space: The maps guide the implementation and enforcement of defensible space regulations, which are crucial for protecting structures from approaching wildfires.
•Emergency Planning: The maps assist in developing effective wildfire mitigation and response plans.
•Designating areas where California’s defensible space standards and wildland urban interface building codes are required.
•General plan considerations: Local governments may consider them in their general plans.
Recent changes in state law, specifically Government Code Section 51179, require local agencies to adopt these maps by ordinance. The City of Palo Alto has received the updated FHSZ map from CAL FIRE, which designates areas within our jurisdiction as Moderate, High, or Very High Fire Hazard Severity Zones. The City’s current adoption of the California Fire Code in the Municipal Code Section 15.04 includes a definition of the Wildland-Urban Interface fire area, that will need to be updated to incorporate the latest CAL FIRE FHSZ map.
This is one of a series of touch points underway regarding wildfire preparedness and response in the City. A news story discussing the conversation was issued on April 28, 20251. The Policy & Services Committee reviewed an audit completed by the City Auditor regarding wildfire preparedness2 and an expanded report outlining activities underway, this was approved unanimously and is scheduled for the Council Consent Calendar. In addition, the following items 1 Palo Alto Begins Wildfire Preparedness Public Discussions; https://www.paloalto.gov/News-Articles/City- Manager/Palo-Alto-Begins-Wildfire-Preparedness-Public-Discussions 2 Policy & Services Committee,
are scheduled in June that continue the conversation around wildfire preparedness for the City of Palo Alto:
•City Council will consider approval of an easement in the Palo Alto foothills to support the undergrounding of the electric transmission line (upon approval by Mid-Peninsula Open Space District).
•Utilities Advisory Commission will review the 2025 Utilities Wildfire Mitigation Plan at their meeting on June 4.
•The City’s Foothills Fire Management Plan updates and the Santa Clara County Community Wildfire Protection Plan, a combined effort will be finalized. •City Council will consider annual weed abatement orders involving private properties.
ANALYSIS
According to CAL FIRE, the maps are developed using a science-based and field-tested model that assigns a hazard score based on the factors that influence fire likelihood and fire behavior.
CAL FIRE is updating these maps to more accurately reflect the zones in California that are susceptible to wildfire, incorporating new science in local climate data and improved fire assessment modeling. The maps evaluate “hazard,” not “risk”. They are 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. Adopting this map is crucial for several reasons:
•Compliance with State Law: State law mandates that local agencies adopt the FHSZ maps.
•Enhanced Public Safety: Adopting the map enables the City to better protect its residents and property from the increasing threat of wildfires. It provides a foundation for implementing effective mitigation measures and enforcing necessary regulations. •Improved Planning and Development: The map will inform land-use planning and development decisions, ensuring that new construction and infrastructure projects are designed to minimize fire risks.
•Access to Funding: Adoption of the FHSZ maps may be a prerequisite for accessing certain state and federal funding for wildfire prevention and mitigation projects. •Understanding Fire Hazard Severity Zones: It is important to note that the Fire Hazard Severity Zone map evaluates "hazard," not "risk." "Hazard" 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. "Risk" is the potential damage a fire can do to the area under existing conditions, accounting for modifications such as fuel reduction projects, defensible space, and ignition-resistant construction.
City staff has reviewed the CAL FIRE FHSZ map and recommends its adoption. A description of how the maps are developed is provided here: Fire Hazard Severity Zones | OSFM. Below summarizes elements of the FHSZ maps and how they were developed.
Key elements of the Fire Hazard Severity Zone model: The fire hazard severity model for wildland fire has two key elements: 1) probability of an area burning and 2) expected fire behavior under extreme fuel and weather conditions. The zones reflect areas that have similar burn probabilities and fire behavior characteristics.
•Factors considered in determining fire hazard within wildland areas are fire history, flame length, terrain, local weather, and potential fuel over a 50-year period. •Outside of wildlands, the model considers factors that might lead to buildings being threatened, including terrain, weather, urban vegetation cover, blowing embers, proximity to wildland, fire history, and fire hazard in nearby wildlands. •FHSZs are not a structure loss model, as key information regarding structure ignition (such as roof type, etc.) is not included.
•The model places an emphasis on the spread of embers. Embers can travel long distances in the wind and ignite vegetation, roofs, attics, and decks. •Areas immediately adjacent to wildland receive the same FHSZ score as that wildland where fire originates, and the model then produces lower scores as the distance to the wildland edge increases.
•In wildland areas, zone edges are a result of the way zones are delineated. Zones represent areas of similar slope and fuel potential.
How Fire Hazard Severity Zones are determined: CAL FIRE used the best available science and data to develop and field-test a model that served as the basis of zone assignments. The model evaluated the probability of the area burning and potential fire behavior in the area. •Many factors were included, such as fire history, vegetation, flame length, blowing embers, proximity to wildland, terrain, and weather.
•A 2 km grid of climate data covering the years 2003-2018 is being used in the update.
The previous model used stock weather inputs across the state to calculate wildland fire intensity scores. The updated model adjusts fire intensity scores based on the most extreme fire weather at a given location, considering temperature, humidity, and wind speed.
•Ember transport is being 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.
•Classification of a wildland zone as Moderate, High, or Very High fire hazard is based on the average hazard across the area included in the zone, which have a minimum size of 200 acres.
•In wildlands, hazard is a function of modeled flame length under the worst conditions and annual burn probability. Classification outside of wildland areas is based on the fire hazard of the adjacent wildland and the probability of flames and embers threatening buildings.
State Responsibility Area (SRA): SRA is the area where the state has financial responsibility for wildland fire protection and prevention. Incorporated cities and federal ownership are not included in SRA. CAL FIRE is responsible for fire prevention and suppression within the SRA.
Local Responsibility Area (LRA): Local Responsibility Areas (LRA) are incorporated cities, urban regions, agricultural lands, and portions of the desert where the local government is responsible for wildfire protection. CAL FIRE uses an extension of the state responsibility area Fire Hazard Severity Zone model as the basis for evaluating fire hazard in Local Responsibility Area.
•The Local Responsibility Area hazard rating reflects flame and ember intrusion from adjacent wildlands and from flammable vegetation in the urban area. •CAL FIRE’s Land Use Planning Program provides support to local governments by providing fire safety expertise on the State’s wildland urban interface building codes, wildfire safety codes, as well as helping in the development of the safety elements in general plans.
•CAL FIRE uses the same modeling data that is used to map the State Responsibility Area for Local Responsibility Areas.
•New legislation, Senate Bill 63 (Stern, 2021), now requires the adoption of all three Fire Hazard Severity Zone classes in the Local Responsibility Area. Previously only Very High Fire Hazard Severity Zones were required for adoption in Local Responsibility Areas.
FISCAL/RESOURCE IMPACT
Adoption of the Ordinance amending the City’s municipal code to adopt the FHSZ map does not have direct fiscal impacts. PAMC 15.04.410 currently identifies the “Wildland-Urban Interface Fire Area” as all areas west of Interstate 280 and all other areas recommended as “Very High Fire Hazard Severity Zone,” and the new map indicates these areas are all within the ”Moderate”, ”High”, or ”Very High” fire hazard severity zone. Because Palo Alto recognizes the indicated areas west of 280 as Wildland Urban Interface (WUI), Chapter 7A of the California Building Code and Chapter 49 of the California Fire Code are already being enforced.
However, additional resources, including staff time and funding for public education, mitigation efforts and outreach may be required. These costs can be absorbed within existing budgets.
Future budget requests may be necessary.
STAKEHOLDER ENGAGEMENT
The City is committed to comprehensive stakeholder engagement throughout the process to adopt and implement updates to the CAL FIRE Fire Hazard Severity Zone (FHSZ) maps. To facilitate public awareness and access to relevant information, the City published details on its official website, and the Uplift Local newsletter, including direct links to supplementary resources. The FHSZ information was made available for a 35-day public comment period.
ENVIRONMENTAL REVIEW
Adoption of the Ordinance amending the City’s Municipal Code to adopt the 2025 FHSZ map does not have a direct environmental impact and is not a project under the California Environmental Quality Act. However, the map will help guide mitigation efforts outlined in the updated Foothills Fire Management Plan (FFMP), which is subject to a CEQA exemption.
ATTACHMENTS
Attachment A: Ordinance amending Section 15.04.410
APPROVED BY:
Geo Blackshire, Fire Chief