Fire Hazard Severity Zones
California’s Fire Hazard Severity Zones
California’s seasonally dry Mediterranean Climate lends itself to wildfires, and in an effort to better prepare, CAL FIRE is required to classify the severity of fire hazards in areas of California.
How are zones determined?
The Fire Hazard Severity Zone 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. Many factors are considered such as fire history, existing and potential fuel (natural vegetation), predicted flame length, blowing embers, terrain, and typical fire weather for the area. There are three levels of hazard in the State Responsibility Areas: moderate, high and very high. Urban and wildland areas are treated differently in the model, but the model does recognize the influence of burning embers traveling into urban areas, which is a major cause of fire spread.
What is the map for?
Implementing wildland-urban interface building standards for new construction
Natural hazard real estate disclosure at time of sale 100-foot defensible space clearance requirements around buildings
Property development standards such as road widths, water supply and signage Consideration in city and county general plans
How do I determine the fire hazard in my area?
Visit the CAL FIRE website at https://egis.fire.ca.gov/FHSZ. You can enter your address to locate your property on a map showing Fire Hazard Severity Zones. An existing statewide map and maps of each county with FHSZ are also posted at https://osfm.fire.ca.gov/divisions/wildfire-planning-engineering/wildland-hazards-building-codes/fire-hazard-severity-zones-maps
While most of California is subject to some degree of fire hazard, there are specific features that make some areas more hazardous. The California Department of Forestry and Fire Protection (CAL FIRE) is required by law 1 to map areas of significant fire hazards based on fuels, terrain, weather, and other relevant factors. These designations, referred to as Fire Hazard Severity Zones (FHSZ), mandate how people construct buildings and protect property to reduce risk associated with wildland fires. The maps were last updated in 2007-2010. They are currently being updated to incorporate improved fire science, data and mapping techniques.The proposed Fire Hazard Severity Zone maps denote lands of similar hazards where the state has financial responsibility for wildland fire protection, known as state responsibility area or SRA, and will be available for review and public comment. It is anticipated that in late 2020 or 2021 CAL FIRE will produce Fire Hazard Severity Zone maps for the areas of California where local governments have financial responsibility for wildland fire protection,known as Local Responsibility Area or LRA. Per law, only lands zoned as Very High Fire Hazard Severity are identified within local responsibility areas.
Fire Hazard Elements
Vegetation - Fire hazard considers the potential vegetation over a 30- to 50- year time horizon. Vegetation is “fuel” for a wildfire and it may vary over time.
Topography - Fire typically burns more quickly and intensely up steep slopes.
Climate - Fire moves faster and is more intense under hot, dry, and windy conditions.
Crown Fire Potential - Under extreme conditions, fires burn to the top of trees and tall brush.
Ember production and movement - Burning embers, known as firebrands, spread fire ahead of the flame front and can ignite buildings up to a mile away from the main fire.
Fire History – Past fire occurrence of an area over several decades.
Extreme fire behavior as the 2018 Ranch Fire burns through the hillsides of Mendocino County.
Frequently Asked Questions
What is a “Fire Hazard Severity Zone,” or FHSZ?
California law requires CAL FIRE to identify areas based on the severity of fire hazard that is expected to prevail there. These areas, or “zones,” are based on factors such as fuel, slope and fire weather. There are three zones, based on increasing fire hazard: medium, high and very high.
How are FHSZ determined?
CAL FIRE used the best available science and data at the time to develop and field test a model that served as the basis of zone assignments. The model evaluated properties using characteristics that affect 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, terrain, and weather.
When were the maps last updated?
In 2007, 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 LRA Local Responsibility Areas.
When will the maps be updated?
CAL FIRE has begun the planning process for updating the FHSZs in 2020. The latest technologies will be used in the mapping and will include new factors now available including land use changes, new significant wind event data, as well as a model that is more spatially detailed.
Why are fire hazard severity maps being updated?
The hazard maps are being updated to more accurately reflect the zones in California that are susceptible to wildfire. The hazard mapping process will incorporate new science in local climate data and improved fire assessment modeling in determining hazard ratings.
Fire Hazard Severity Zones
What does FHSZ measure?
Fire Hazard Severity Zone maps evaluate “hazard,” not “risk”. They are like flood zone maps. “Hazard” is based on the physical conditions that create a likelihood and expected fire behavior over a 30 to 50-year period without considering short-term modifications such as fuel reduction efforts. “Risk” is the potential damage a fire can do to the area under existing conditions, including any modifications such as fuel reduction projects, defensible space, and ignition resistant building construction.
Where do Fire Hazard Severity Zones Apply?
Fire Hazard Severity Zones are found in areas where the State has financial responsibility for wildfire protection and prevention, called the State Responsibility Area. More than 31 million acres are in this area. Very High Fire Hazard Severity Zones are found in local jurisdictions as well.
What are the uses of Fire Hazard Severity Zones?
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.
Is there an easy way to determine the FHSZ of my property?
If you know your address you can find the designation on the web at: https://egis.fire.ca.gov/FHSZ/
Fire Hazard Severity Zone Model Used by CAL FIRE
What are the key elements of the Fire Hazard Severity Zone model?
The fire hazard severity model for wildland fire has two key elements: probability of an area burning and expected fire behavior. Hence, the factors considered in determining fire hazard are how often an area will burn and, when it does burn, what characteristics might lead to buildings being ignited. FHSZs are not however a structure loss model, as key information regarding structure ignition (such as roof type, etc) is not included.
In the model, Fire Hazard Severity Zones are areas that have similar burn probabilities and fire behavior characteristics. In wildland areas, expected fire behavior is based on typical fire intensity on a normally severe fire weather day. The calculation also incorporates fire brand production and spot fire potential.
What is the difference between the various Fire Hazard Severity Zones?
Classification of a zone as moderate, high or very high fire hazard is based on a combination of how a fire will behave and the probability of flames and embers threatening buildings. Each area of the map gets a score for flame length, embers, and the likelihood of the area burning. Scores are then averaged over the zone areas which vary in size from relatively small – 20 acre urban areas to larger wildland zones that have minimum size of 200 ac. Final zone class (moderate, high and very high) is based on the averaged scores for the zone.
Why does the model place an emphasis on the spread of burning embers?
Embers spread wildfire because they can travel long distances in the wind and ignite vegetation, roofs, attics (by getting into vents), and decks.
Fire Hazard Severity Zone and Building Standards in the State Responsibility Area
SRA is a legal term defining the area where the State has financial responsibility for wildland fire protection and prevention. Incorporated cities and federal ownership are not included. Within the SRA, CAL FIRE is responsible for fire prevention and suppression. There are more than 31 million acres in SRA with an estimated 1.7 million people and 800,000 existing homes.
The Board of Forestry and Fire Protection (Board) classifies land as State Responsibility Area. The legal definition of SRA is found in the Public Resources Code Section 4125. The Board has developed detailed procedures to classify lands as State Responsibility Area. Lands are removed from SRA when they become incorporated by a city, change in ownership to the federal government, become more densely populated, or are converted to intensive agriculture that minimizes the risk of wildfire. While some lands are removed from SRA automatically, the Board typically reviews changes every five years.
All of the State Responsibility Area is in a Fire Hazard Severity Zone. Lands are either ranked as Moderate, High or Very High Fire Hazard Severity Zones.
The 2008 building codes (California Building Code (CBC) Chapter 7A) reduce the risk of burning embers fanned by wind-blown wildfires from igniting buildings. Roofing standards vary by the fire hazard zone rating of the site. The codes for siding, decking, windows, and vents apply throughout all state responsibility area regardless of the fire hazard severity ranking. Ember-resistant building materials can be found at: https://www.readyforwildfire.org/prepare-for-wildfire/get-ready/hardening-your-home/
Very High Fire Severity Hazard Severity Zones in Local Responsibility Areas
Local Responsibility Areas (LRA) are incorporated cities, urban regions, agriculture lands, and portions of the desert where the local government is responsible for wildfire protection. This is typically provided by city fire departments, fire protection districts, counties, and by CAL FIRE under contract.
The “Bates Bill” (AB 337), Government Code Section 51175, was prompted by the devastating Oakland Hills Fire of 1991. This mid-1990s legislation calls for CAL FIRE to evaluate fire hazard severity in local responsibility area and to make a recommendation to the local jurisdiction where very high FHSZs exist. The Government Code then provides direction for the local jurisdiction to take appropriate action.
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. Scientists at the U. C. Berkeley Center for Fire Research and Outreach provided an urban fuels model that was incorporated in the hazard rating.
California’s wildland building codes (CBC Chapter 7A) apply to the design and construction of new buildings located in very high FHSZs in Local Responsibility Areas. Local ordinances may require ignition resistant construction for remodel projects. Check with your local building department to determine which ignition resistant building codes apply to your project. In addition, Government Code Section 51182 calls for defensible space clearance and other wildland fire safety practices for buildings. Owners are also required to make a natural hazard disclosure as part of a real estate transfer. For information regarding “home hardening” and defensible space clearance, visit www.ReadyForWildfire.org.
Yes, per Government Code 51182 unless a local government has passed a more stringent requirement, the 100-foot defensible space clearance apply.
CAL FIRE’s Land Use Planning Program is a specialized unit that 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. Currently there are 189 cities and 56 counties with FHSZ.
CAL FIRE uses the same modeling data that is used to map the State Responsibility Area. The department works with local jurisdictions for validation of the mapping. The map, along with a model ordinance, are then sent to the governing body for adoption.
How do the Fire Hazard Severity Zone Maps differ from the CPUC High Fire Threat District Maps?
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 the purpose of 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 score areas based on where fires start, as opposed to where potential fires may cause impacts.
Need more Information?
The California laws that require Fire Hazard Severity Zones include
California Public Resource code 4202-4204 and California Government Code 51175-89.
For additional information about Fire Hazard Severity Zones or wildland-urban interface building codes,
visit www.OSFM.fire.ca.gov, or contact your local CAL FIRE Unit.