What Is Wildfire Risk and How Is It Measured?
Wildfire risk is a measure of how likely a structure is to ignite and be damaged during a wildfire event, based on the combination of hazard (fire environment), exposure (proximity to wildlands), and vulnerability (construction and preparedness). Unlike most natural disaster risk assessments, wildfire risk is highly actionable — property owners can reduce their risk level significantly through defensible space maintenance and home hardening, often without relocating or rebuilding.
Official wildfire risk assessments are conducted by state fire agencies using Fire Hazard Severity Zone (FHSZ) maps, which classify land as Moderate, High, or Very High risk based on fuel load, fire weather, and topography. This property-level assessment goes further by evaluating the five factors that research has shown to most directly determine whether an individual structure survives a wildfire: location and environment, home construction materials, defensible space, home hardening, and emergency readiness.
Wildfire Risk by State: Where Is Risk Highest?
Wildfire risk is not evenly distributed across the United States. The following table summarizes risk levels by state based on FEMA's National Risk Index, CAL FIRE data, and USFS WUI mapping as of 2025. States marked High or Very High have significant populations in designated Fire Hazard Severity Zones.
| State | Risk level | WUI homes (est.) | Key driver |
|---|---|---|---|
| California | Very High | ~6.7 million | 31M+ acres of FHSZ; drought; Santa Ana winds |
| Oregon | Very High | ~1.3 million | Cascade Range; eastern Oregon grasslands |
| Washington | Very High | ~1.1 million | Eastern WA shrub-steppe; Okanogan Highlands |
| Colorado | High | ~900,000 | Front Range WUI; Marshall Fire precedent (2021) |
| Montana | High | ~480,000 | Northern Rockies; pine and fir fuel loads |
| Idaho | High | ~420,000 | Bitterroot Range; Sawtooth National Forest |
| Arizona | High | ~600,000 | Chaparral; Mogollon Rim; low humidity |
| Texas | Moderate–High | ~1.8 million | West TX grasslands; Panhandle wind events |
| New Mexico | Moderate–High | ~290,000 | Sangre de Cristo Range; Hermit's Peak fire (2022) |
| Nevada | Moderate | ~280,000 | Great Basin shrublands; Reno growth into WUI |
| Florida | Moderate | ~1.2 million | Pine flatwoods; Panhandle; frequent prescribed fire escapes |
| All other states | Low–Moderate | Varies | Localized WUI pockets; risk increasing in southeastern US |
The 5 Factors That Determine Whether Your Home Survives a Wildfire
Research from the Insurance Institute for Business and Home Safety (IBHS) and UC Cooperative Extension has identified five property-level factors that predict structure survival during wildfire with the greatest consistency. This assessment is structured around these same five areas.
1. Environment and location
Proximity to wildland vegetation, local fire history, and terrain are the baseline risk factors — the ones you cannot change without moving. Homes within 30 feet of wildland fuels on steep slopes with documented wildfire history are in the highest-risk environment category regardless of other measures taken. Slope matters enormously: fire travels roughly twice as fast for every 10-degree increase in slope angle, which means a home at the top of a canyon can face a fire front that arrives in minutes rather than hours.
2. Home construction materials
The materials your home is built with determine how easily it can be ignited by radiant heat, direct flame contact, or ember accumulation. The most critical component is the roof. According to CAL FIRE, ember accumulation in roof valleys, gutters, and eaves accounts for approximately 40 percent of structure ignitions during wildfire events. Class A fire-rated roofing — metal, concrete or clay tile, or asphalt composite shingles — provides the highest level of protection. Combustible wood shake or shingle roofing is the single highest-risk construction feature a WUI home can have.
3. Defensible space
Defensible space is the managed vegetation buffer between a home and surrounding wildland fuels. California Code of Regulations Title 14 and NFPA 1144 both require two zones. Zone 1 (0 to 30 feet) must be free of dead vegetation, dry leaves, wood piles, and bark mulch, with grass kept under 4 inches and tree limbs pruned to 10 feet from the ground. Zone 2 (30 to 100 feet) requires horizontal and vertical spacing of tree crowns, removal of ladder fuels, and regular mowing. On slopes steeper than 30 percent, Zone 1 requirements extend to 100 feet uphill and to the sides.
4. Home hardening
Home hardening refers to structural modifications that reduce ignition pathways. IBHS ember research has shown that 90 percent of homes destroyed in wildfires ignite from ember intrusion or accumulation — not direct flame contact. The three highest-impact hardening measures are: replacing open or large-mesh vents with 1/8-inch corrosion-resistant metal mesh; replacing combustible bark mulch within 5 feet of the foundation with rock, gravel, or decomposed granite; and replacing or enclosing attached combustible decks. Many of these improvements also qualify for homeowner's insurance discounts.
5. Emergency readiness
Emergency readiness determines what happens when a wildfire does approach. Research consistently shows that the single largest predictor of evacuation survival is leaving early — at the first Evacuation Warning, not the Evacuation Order. This requires a practiced two-route evacuation plan, enrollment in local emergency alert systems, and a packed go-bag ready for immediate departure. The Camp Fire in 2018 and the Marshall Fire in 2021 both produced evacuation windows of less than 20 minutes for some neighborhoods.
Understanding Your Wildfire Risk Score
This assessment produces a preparedness score from 0 to 100, divided across five weighted categories. The weighting reflects the relative contribution of each factor to structure survival probability based on published wildfire research.
| Score range | Risk level | What it means |
|---|---|---|
| 81–100 | Low risk | Strong protections across all five areas. Maintain annually. |
| 66–80 | Low-moderate risk | Good foundation with a few gaps worth closing this season. |
| 51–65 | Moderate risk | Several important protections missing. Action within 60 days. |
| 31–50 | High risk | Significant vulnerabilities. Prioritize before fire season. |
| 0–30 | Extreme risk | Critical exposures requiring immediate action. |
How to Lower Your Wildfire Risk: Priority Actions by Category
Defensible space: highest return on time invested
Clearing Zone 1 to CAL FIRE standards typically takes a single weekend for most residential lots and can be done without professional help. Remove all dead plants and dry leaves, prune tree limbs to 10 feet from the ground, replace bark mulch with gravel, and relocate any wood piles or propane tanks to at least 30 feet from structures. This single category accounts for 25 of the 100 possible points in this assessment.
Home hardening: highest return on dollars spent
Vent screening is the most cost-effective home hardening upgrade available. A full set of 1/8-inch metal mesh vent covers for a typical single-family home costs between $200 and $600 in materials and can be installed in a day. This single step addresses the primary ember intrusion pathway responsible for the majority of wildfire structure ignitions. Replace combustible bark mulch within 5 feet of the foundation with inorganic ground cover — rock, decomposed granite, or concrete — for additional ember accumulation protection.
Emergency readiness: highest return on preparedness
Register for your county's emergency alert system today by searching "[your county] emergency alerts." Pack a go-bag with 72 hours of supplies: water (1 gallon per person per day), non-perishable food, a full set of current prescription medications, important documents in a waterproof folder (IDs, insurance policies, deed, passport), a phone charger, cash, N95 masks, one change of clothing per person, and pet food and carrier if applicable. Write down and practice two evacuation routes. Tell a household member outside your immediate area where you will go.