CAL FIRE
Fire Hazard Severity Zones
What are the Zones?
• The maps are required by
Government Code 51178 & 51179
• Identify levels of fire hazard
• • 3 levels (Moderate, High, & Very High)
Fire Hazard Fire Hazard Severity Zones Severity Zone Remap How are the Zones 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. • Factors: fire history, vegetation, flame length, blowing embers, proximity to wildland, terrain, and weather
Fire Hazard Fire Hazard Severity Zones Severity Zone Remap New Updates
• Updated burn probabilities for wildland areas
(inclusive of 2020 fires)
• Updated fire environment footprints (urban/developed) • Updated Vegetation density for urban areas
• Inclusion of slope in the urban zoning model
• Localized fire weather used in both wildland and urban models
• New firebrand production and transport model using
discrete local wind vector distributions
Fire Hazard Severity Zones
New Updates
Wildland vs. Non-wildland Zones
• Zones are areas with relatively
homogeneous slope and vegetation
• Hazard map is produced at 30 m resolution
• Scores are averaged within a zone
• Wildland is scored independently of urban
and agricultural
• Urban zones scored using additional model
steps
Fire Hazard Fire Hazard Severity Zones Severity Zone Remap Wildland FHSZ
• Minimum size of 200 acres
• Burn probability
– Based on fire occurrence from 1991-2020
• Fire intensity
– Vegetation type
– Slope
– Local fire weather – how hot/dry/windy are
the worst conditions at a given location
(based on 2 km data from 2003-2018)
Fire Hazard Fire Hazard Severity Zones Severity Zone Remap Urban FHSZ
• Minimum size of 20 acres for isolated islands of vegetation embedded in non-wildland.
• Based on distance to wildland and hazard level of adjacent wildland
• Ember production based on vegetation type and fire weather • Ember transport based on wind speed/direction observed under the most extreme fire weather at a given location • Width of moderate, high and very high bands in urban are based on ember load, urban tree cover and slope
Fire Hazard Fire Hazard Severity Zones Severity Zone Remap What is the map for?
• Building standards for new construction in the
Wildland-Urban Interface (California Building Code
Chapter 7A)
• Property development standards such as road
widths, water supply and signage (Fire Safe
Regulations)
• Defensible Space Requirements (Government
Code 51182)
• Natural hazard real estate disclosure
Fire Hazard Fire Hazard Severity Zones Severity Zone Remap Fire Hazard Severity Zones New Updates
What’s Impacted…
Adoption Timeline:
Fire Hazard Fire Hazard Severity Zones Severity Zone Remap Questions?
osfm.fire.ca.gov/fhsz