San Leandro Fire Hazard Severity
Zone (FHSZ) Map Update
May 19, 2025
1 Why We’re Here
•Repeal of 2009 ordinance
•Adoption of newly released 2025
FHSZ maps
2 What Are Fire Hazard Severity Zones?
• Created by CAL FIRE
• Zones are used to classify level of wildfire hazard
based on factors like fuel load, topography, weather,
and fire history
• Measure *hazard* (not risk)
• Zones inform building standards, land use planning,
insurance, and public safety measures
3 A Brief History of Fire Hazard Zones
4 Year Event
Pre-2000s
No statewide fire hazard mapping for Local Responsibility Areas (LRAs)
2005
State law mandates CAL FIRE to map LRA fire hazard
zones under Government Code § 51175–51189.
2008 First LRA FHSZ maps released (Moderate, High, Very High) 2008+ Local governments begin adoption of Very High Zones 2025
CAL FIRE’s latest maps incorporate modern fire science, modeling, and statewide data consistency.
Hazard vs. Risk
• Hazard = Physical environment (vegetation, slope, weather) • Risk = A combination of hazard and human factors - like proximity to homes, roads, evacuation constraints, and preparedness • San Leandro's risk remains high, despite map changes
• But the hazard mapping update better isolates where the most extreme fire behavior is likely, based on new science
• FHSZ maps are regulatory triggers, not predictive tools 5 2009 vs 2025 Map Comparison
• 2009: 'Very High' zones adopted based on best
available data at the time
• 2025: CAL FIRE removed all 'Very High'
designations in San Leandro
• Instead, they designate zones as High or Moderate
hazard — a reflection of refined data, not a
reduction in fire danger or risk
6 2009 Map
• Only the Very High Zone
was evaluated in the Local
Response Area (LRA) in
2007-2011.
• San Leandro had 557
parcels in the Very High
Fire Hazard Severity Zone
7 2025 Map
• The LRA 2025 evaluation
included Very High, High,
and Moderate
• Results:
• 443 parcels in High
• 184 parcels in
Moderate
• Grand total of 627
8 Map Comparison
9 • 360 parcels that used to be
Very High are now High
• 41 parcels that used to be
Very High are now Moderate
• 156 parcels that used to be
Very High are now NonWildland
Science Behind the Maps
10 • The maps estimate long-term wildfire hazard potential across California, focusing on areas where wildland and urban environments meet. • Zones are categorized as Moderate (M), High (H), or Very High (VH) based on burn probability and expected fire behavior.
• Two Modeling Tracks:
• Wildland Areas: Modeled using fire behavior science (spread, intensity) and historic burn data.
• Non-Wildland Areas (WUI): Modeled based on ember (firebrand) exposure from adjacent wildlands and likelihood of ignition/spread through urban vegetation.
Wildland Modeling
11 • Two Key Components
• Burn Probability: Based on 30 years of fire history (1991– 2020), vegetation, and climate types.
• Fire Behavior: Potential flame length calculated using slope, vegetation type, and extreme local fire weather.
• Worst-Case Conditions: Models use the hottest, driest, windiest 5% of weather days that can sustain fire.
• Long-Term Perspective: Does not factor in recent fires or fuel treatments, focusing instead on hazard potential over decades.
Non-Wildland Modeling
12 • Focuses on embers landing from adjacent wildlands and conditions promoting ignition and spread.
• Three Inputs:
1. Brand Load (number of embers landing, based on flame length and wind)
2. Slope (>20% = more hazardous)
3. Tree Cover (more trees = higher ignition potential)
• A “cost surface” is calculated from these inputs to determine how far hazard extends into developed areas.
• Buffers of decreasing hazard classes (from VH to M) are mapped outward from wildland boundaries based on these values.
Zone Construction Summary
13 • Zones are defined by areas with similar fire behavior potential. • Final hazard score per zone is an average of all grid cell scores within it.
• Map updates incorporate:
• New climate and fire weather data
• Improved ember modeling
• Localized vegetation and slope detail
• Advanced burn probability modeling
What the Maps Trigger
• CBC Chapter 7A: Fire-resistant construction for new
buildings
• Gov Code 51182: Mandatory defensible space
enforcement
• Natural Hazard Disclosure: Home sale disclosure of
Very High and High zones
14 Local Authority to Designate Additional Very
High Zones
• No Local Changes to State Designations
• Cities cannot reduce or request modifications to CAL FIRE’s designated hazard zones.
• Expansion Is Allowed
• Under Gov. Code §51179(b)(1), local agencies may add areas not identified by CAL FIRE as Very High Fire Hazard Severity Zones, if justified. • Requirements for Local Designation:
• Must be supported by substantial evidence in the record • Must find that applying defensible space laws (Gov. Code §51182) is necessary for effective fire protection
15 Potential Benefits of Requesting “Very
High” Designation
• Stronger public awareness and risk perception
• Enables local defensible space enforcement
16 Potential Downside of Requesting
“Very High” Designation
• Mandates local inspections and enforcement
• Comes with significant cost, administrative demand, and legal complexity
• May reduce compliance and trust
• Why many cities opt for education-first strategies rather than formal zoning or enforcement.
17 What Other Cities Are Doing
• Berkeley: Mandating compliance
• Marin County: Most cities opted for voluntary
compliance
• Focus on:
• Homeowner education
• Outreach and defensible space support
• Community resilience over mandates
18 What’s In Our Control
19 Issue Who Controls It Can the City Change It?
FHSZ Maps CAL FIRE
Yes* – City may add
zones with justification
Insurance
Insurance
Companies
No
Defensible Space
Enforcement City Yes
Education & Outreach City Yes
City Fire Safety Efforts
• Continued annual Defensible Space Inspections of High FHSZ areas
• Chipper Program
• Community Preparedness Training
• Emergency Preparedness Workshop May 20 & June 11
• Community Emergency Response Training (CERT)
o May 29, 31, June 7
• Personal Emergency Preparedness
• Red Flag Days - Engine upstaffing and patrolling
20 fire.acgov.org
Zone 0: Ember-Resistant Zone 0 – 5 feet from
building
Zone 1: Lean, Clean, and Green Zone 5 – 30 feet
from the building
Zone 2: Reduce Fuel Zone 30-100 feet from the
building or to the property line
Request a Defensible
Space Inspection
[email protected]
Take an interactive
look at the CalFire
Wildfire Action Plan
ACFD Defensible Space Inspection FAQs
Fire Hazard Severity
Zone Locator
ACFD Chipper Program
21 Defensible Space Inspections
22 fire.acgov.org/emergency-preparedness/