City of Irvine
2020 Local Hazard Mitigation Plan
more than any other hazard event. The most destructive and deadliest fire in the state’s history is the 2018 Camp Fire in Butte County. This fire destroyed nearly 19,000 structures and killed 85 people. 112
Wildfires can be sparked by lightning, accidents, or arson. The size and severity of any fire depends on the availability of fuel, weather conditions, and topography, although wildfires in the WUI do not need to be large to be damaging. The 1991 Tunnel Fire in Oakland was relatively small, only 1,600 acres, but was the second deadliest and third most destructive wildfire in California history. 113 The flames from wildfires create serious risks to property and lives. Smoke and other particulate matter from wildfires pose a health risk, even to those not in the immediate vicinity of the blaze. Burned areas can be more susceptible to flooding and landslides because wildfires destroy the vegetation that helps to slow down water runoff and holds slopes together.
Wildfires have been a regular part of the landscape in the Orange County region. This sign, which used to stand at the Top of the World, showed the localized fire danger. Image from Patrick Nouhailler.
Location and Extent
Wildfires are not measured on a specific scale and are usually classified by size (e.g., acres burned) or impact (buildings destroyed or damaged, injuries or deaths, cost of damage, etc.). The risk of wildfire is classified on a three-tier scale of fire hazard severity zones (FHSZs): very high, high, and moderate. These classes do not correspond to a specific risk or intensity of fire but are qualitative terms that consider many factors. Fire-prone areas are also classified by the agency responsible for fire protection. Federal Responsibility Areas (FRAs) fall to federal agencies such as the US Forest Service, the Bureau of Land Management, and the National Park Service. State Responsibilities Areas (SRAs) fall to the California Department of Forestry and Fire Protection (CAL FIRE), and Local Responsibility Areas (LRAs) fall to local governments. The topography of the foothills of the Santa Ana Mountains and San Joaquin Hills in Irvine is extremely conducive to wildfires. The community is bordered by natural, undeveloped hillsides/ mountains to the northeast and open space areas to the southwest. In between these two areas is most of the City’s developed areas. A majority of these natural, undeveloped areas are classified as Very High Fire Hazard Severity Zones (VHFHSZ) by Cal FIRE. In the northeastern portion of the City, this zone extends throughout the Santa Ana Mountain range, which extends into Riverside County to the east. Figure 3-13 depicts the fire hazard severity zones mapped throughout the City and surrounding areas. These zones range from moderate to extreme fire hazard potential. Figure 3-14 depicts the Very High Fire Hazard Severity Zones adopted by Cal FIRE and the City. This zone delineates the regulatory requirement that triggers compliance with Government Code Section 65302 (g) 3 [also known as SB 1241].
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