Fire Hazard Severity Zone Re-Mapping Project



Introduction / Background

PRC 4201-4204 and Govt. Code 51175-89 direct the California Department of Forestry and Fire Protection (CDF) to map areas of significant fire hazards based on fuels, terrain, weather, and other relevant factors. These zones, referred to as Fire Hazard Severity Zones (FHSZ), then define the application of various mitigation strategies to reduce risk associated with wildland fires. State Responsibility Area (SRA) was originally mapped in 1985 and has not been updated since, except with respect to changes in SRA boundaries. Local Responsibility Areas (LRA) were originally mapped in 1996, and also has not been updated since, although many local governments have made similar designations under their own authority. Current FHSZ is available for 1985 SRA, 2007 SRA and LRA.

CDF wishes to remap both SRA and LRA areas to provide updated map zones, based on new data, science, and technology that will create more accurate zone designations such that mitigation strategies are implemented in areas where hazards warrant these investments. The zones will provide specific designation for application of defensible space and building standards consistent with known mechanisms of fire risk to people, property, and natural resources.

Project Description

The project will be driven by Geographic Information System (GIS) data in conjunction with modeling techniques designed to describe potential fire behavior and fire probability. Areas will be mapped in Moderate, High and Very High Categories. The project will run along two concurrent tracks: one designed to develop and refine the model itself regarding its scientific rigor, spatial accuracy, and data delivery mechanisms designed to facilitate end use by a wide variety of clients. The other track will focus on the roll-out and implementation process whereby local CDF units and local fire agencies review/comment and adjust the zones to conform to local knowledge not captured in the draft model.

Finally, the maps will follow established adoption processes required by state statute, and be made available by Jan 1, 2008, consistent with implementation of new Wildand-Urban Interface (WUI) building codes that have been adopted by the California Building Standards Commission.

Model Development

The basic elements of the Fire Hazard Zone model will be built from existing data and hazard constructs developed by CDF's Fire and Resource Assessment Program (FRAP) used to develop Fire Threat and Communities at Risk listing in the Federal Register pursuant to the National Fire Plan (see for details). The model will work from these products as starting points, and refine characterization of the zones to directly attempt to characterize fire exposure mechanisms that cause ignitions to structures. These basic constructs follow classical quantitative risk assessment whereby probabilities of fire behaviors define the hazard component of risk analysis. CDF FRAP is partnering with researchers at UC Berkeley and the private sector to develop this model and it promises to use innovative techniques to meet the objectives and usage of the data.

Specific model components will focus on characterizing potential fire behavior arising for vegetation fuels that are by nature dynamic. Since many of the applications of the zones involve permanent engineering mitigations associated with structure construction, it is desirable that the nature of the zone reflect changes in fire behavior/exposure relative to the length of time the structure will be in place. While obviously significant land-use changes will need to be captured through period maintenance routines, basic vegetation dynamics and maximal hazard levels will be used to develop the model such that mitigations match potential exposure over the horizon of the mitigation design.

The model will also incorporate a measure of fire probability predicated on frequency of fire weather, ignition patterns, expected rate-of spread, and/or past fire history similar to techniques uses to calculate fire rotation as used in the development of Fire Threat. A detailed description of components used in Fire Threat can be found here.

Finally, the model will characterize flying ember (brand) production from vegetation fuels, and zoning hazard based on the area of influence that those brands are likely to land and cause potential ignitions. This functional mechanism of hazard is the principal driver of hazard in densely developed areas. A related concern in already built-out areas is the relative density of vegetative fuels that can serve as receptive sites for new spot fires to initiate within the urban core, and then spread to adjacent structures. The project will explore techniques to model accurately both the brand production/reception element, as well as fire spread potential in urbanized areas.

Additional details regarding planning for map implementation will follow as they become available.

Timeline for future work

Draft model maps will be presented to four pilot counties (Butte, Calaveras, San Diego, and Sonoma) will be reviewed at workshops and in the field over the course of July and August, 2006. Changes to the model based on these reviews will be incorporated into the final draft model methodology.

A science-peer review process will follow in September, 2006, resulting in final model methodology.

Statewide DRAFT mapping will commence in September and be completed by December, 2006.

Final model packaging for outreach, review, validation and implementation will be completed by February 1, 2007.

For SRA lands, systematic map review implementation, and adoption procedures will be conducted over the Jan.-Dec., 2007 period, including public hearings and comment from June through September, with final adopted zones completed by Jan.1, 2008.

For LRA lands, draft maps will be provided to local agencies for review and comment from November 2007 - March 2008, with transmittal of recommended Very High zones beginning in March 2008.

For more information on Hazard Mapping and associated Building Codes, please see

For more information, please contact:

Dave Sapsis
Wildland Fire Scientist
CDF Fire and Resource Assessment Program (FRAP)
PO Box 944246
Sacramento, CA 94244-2460


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