Questions about fire hazard severity zones
What is a “Fire Hazard Severity Zone,” or FHSZ?Answer: 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 (material that can burn), slope and fire weather. There are three zones, based on increasing fire hazard…medium, high and very high.
Answer: Using the latest fire science, CAL FIRE has developed and field tested a model that serves as the basis of zone assignments. The model evaluates property using characteristics that affect the probability of the area burning and potential fire behavior in the area. Many factors are considered such as fire history, existing and potential fuel, flame length, blowing embers, terrain, weather and the likelihood of buildings igniting.
Answer: 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 that an area will burn over a 30 to 50-year period without considering 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 defensible space, irrigation and sprinklers, and ignition resistant building construction.
How have the Fire Hazard Severity Zone Maps changed?
Answer: Statewide, the acreage designated as very high Fire Hazard Severity Zones is reduced by 25 percent, the acreage designated as high Fire Hazard Severity Zones is increased by 57 percent, and the acreage designated as moderate Fire Hazard Severity Zones is increased by 33 percent. For detailed information on acreage changes by county, visit Publications. These changes are largely due to the ability to be more precise. In the previous map version, typically a minimum 10,000-acre zone size was used resulting in large areas of land being designated based on the highest hazard level found in that entire area. Refined modeling techniques and new, more precise data describing the potential fire environment has enabled the use of 200-acre parcel sizes in many cases which makes mapping more spatially refined. In addition, improved mapping science and a thorough model allowed for more consistency in how zones are rated.
Answer: Statewide, the acreage designated as very high Fire Hazard Severity Zones is reduced by 25 percent, the acreage designated as high Fire Hazard Severity Zones is increased by 57 percent, and the acreage designated as moderate Fire Hazard Severity Zones is increased by 33 percent. For detailed information on acreage changes by county, visit Publications. These changes are largely due to the ability to be more precise. In the previous map version, typically a minimum 10,000-acre zone size was used resulting in large areas of land being designated based on the highest hazard level found in that entire area. Refined modeling techniques and new, more precise data describing the potential fire environment has enabled the use of 200-acre parcel sizes in many cases which makes mapping more spatially refined. In addition, improved mapping science and a thorough model allowed for more consistency in how zones are rated.
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