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Not every wildfire spreads through forests. Some move house to house, block to block, driven by wind, heat, and proximity. As these events become more common, insurers are asking sharper questions about how to assess risk in densely built environments. Z-FIRE was designed to account for the real-world conditions that enable this type of fire behavior, capturing the structural, spatial, and environmental factors like building density, defensible space, mitigation strategy, climatology, and slope that contribute to urban conflagration.
What Is Urban Conflagration?
Urban conflagration refers to a fire that spreads rapidly through a densely built environment, jumping from structure to structure rather than moving solely through vegetation. Unlike traditional wildfires that primarily burn forests or grasslands, these events are driven by building materials and the adoption of fire mitigation practices, the spacing between structures, and proximity to areas that are known to be challenging for firefighters. Wind and terrain—particularly steep slopes—often accelerate the spread, pushing fire fronts into residential areas and compounding the risk of widespread destruction. For insurers, urban conflagrations represent a uniquely challenging peril, where fire behavior is shaped as much by the built environment as by natural fuels. Without a model built to capture these dynamics, they’re nearly impossible to assess accurately.
We’ve seen what happens when wind-driven embers reach tightly packed communities. In fires like Marshall, Lahaina, and the recent Palisades and Eaton Fires, wildfires didn’t stop at the wildland-urban interface—they became full-scale urban conflagrations. These events are stark reminders that wildfire risk doesn’t end at the edge of the forest and that densely populated areas can produce concentrated, catastrophic losses.
For insurers, these events raise a critical question: Where are the next high-concentration loss scenarios hiding in the portfolio?
When urban conflagration strikes, damage rates spike, and PML exposure can increase exponentially. Identifying the neighborhoods where construction patterns, terrain, and fuel conditions create the potential for that kind of fire behavior is no longer optional; it’s essential.
At ZestyAI, we’ve been asking, and answering, these questions for years. The Z-FIRE model was designed to do exactly that.
Built to Reflect Real-World Urban Risk
From its inception, Z-FIRE has accounted for the drivers of urban conflagration. Its two-level architecture combines neighborhood-level dynamics with property-specific characteristics, offering a detailed and scalable view of wildfire risk—even in densely built environments.
Level 1 (L1): Neighborhood Risk Score
L1 predicts the likelihood that a property will fall within a wildfire perimeter. It does this by analyzing climatology, historical wildfire behavior, terrain, fuel type, and wildfire suppression ratings to understand where fires are likely to start, spread, and grow.
Two variables are particularly important for identifying urban conflagration risk:
- Fuel Type, which accounts for both vegetative fuels and the built environment. In densely developed areas, clusters of structures can serve as fuel, particularly when combined with slope, dry conditions, or limited defensible space.
- Wildfire Suppression Rating (WSR), which indicates areas where fire suppression is likely to fail due to access, water availability, or firefighting capacity. Rather than relying on WSR alone, Z-FIRE factors in proximity to high and very high WSR zones, enabling it to capture risk spillover into nearby neighborhoods.
What sets Z-FIRE apart is how these variables interact. The model doesn’t assess them in isolation—it evaluates how multiple risk factors compound one another. This layered, interaction-driven approach allows Z-FIRE to surface hidden vulnerabilities that simpler, one-dimensional models often miss and accurately identify regions with high conflagration risk.
- L1 evaluates wildfire risk based on local terrain, fuel types, and building density. Critically, Z-FIRE incorporates two critical variables that are key indicators of conflagration risk. Both “fuel type” and proximity to areas with a High or Very High wildfire suppression rating.
- Fuel Type accounts for both vegetation and for developed land characteristics. While vegetative fuel and its management are key for wildfire, building density can become a large contributor to conflagration risk if combined with the other high-risk factors. It is important to remember that Z-FIRE allows for unlimited variable interaction; a high-density neighborhood can be at high risk of other factors, contributing to conflagration risk.
- Wildfire Suppression Rating (WSR) reflects the risk that a high-intensity fire may become impossible to manage by firefighters. Because those areas tend to be located in the WUI, Z-FIRE does not only rely on the WSR score, but also uses the distance proximity to high or very high WSR.
Level 2 (L2): Property-Specific Risk Score
At the structure level, L2 evaluates both nearby vegetation and building fuel density, a key driver of structure-to-structure ignition. This metric, validated by the Insurance Institute for Business & Home Safety (IBHS), helps Z-FIRE model how a single ignition can escalate within tightly packed neighborhoods, even in the absence of natural fuels.
Z-FIRE was trained on real-world events with clear urban conflagration patterns. In the 2017 Tubbs Fire, for example, flames spread deep into Santa Rosa, destroying dense subdivisions like Coffee Park. Similarly, recent fires such as Palisades and Eaton moved rapidly through built-up areas, where tightly spaced structures provided a continuous path of fuel.
Case in Point: Palisades and Eaton, CA
In the recent Palisades and Eaton Fires, Z-FIRE’s predictive accuracy was once again put to the test. Our analysis showed that over 91% of the affected area was already classified by Z-FIRE as high or very high risk based on Level 1 (L1) neighborhood scores. Notably, none of the impacted areas were categorized as “Very Low Risk,” a strong validation that Z-FIRE captured the inherent vulnerability of these communities well before ignition.
Looking at Level 2 (L2) property-specific scores, the correlation between predicted risk and actual destruction became even clearer.
Structures with the highest Z-FIRE risk scores were 50% more likely to be destroyed compared to those with the lowest scores in the same fire footprint.
These destruction rates align with the model’s fundamental architecture: properties with denser surrounding structures, minimal defensible space, and combustible fuels nearby face a dramatically higher likelihood of loss during a wildfire.
The model identified risk in this community not simply based on topography or vegetation, but because of its underlying urban structure, including building materials, spacing between homes, and neighborhood density. These are the very factors that drive vulnerability to conflagration.
Z-FIRE was designed to capture these dynamics, reinforcing its value as a forward-looking tool for rating, underwriting, and mitigation planning.
A Model Informed by What’s Happening on the Ground
Wildfire conditions are constantly changing, and Z-FIRE stays current by continuously incorporating the latest ground-truth data, including updated fire perimeters, confirmed loss locations, and vegetation conditions. While the core model remains stable and fully approved for rating and underwriting, this steady stream of fresh data ensures that Z-FIRE reflects the most recent fire seasons and emerging risk patterns.
The 2023 and 2024 fire seasons reinforced what we’ve long understood: fire behavior is increasingly shaped by the built environment. Z-FIRE continues to perform as expected across a wide range of scenarios, including structure-to-structure ignition in densely built areas. These results reaffirm the model’s ability to provide timely, reliable insights to support carrier decision-making in a rapidly evolving risk landscape.
Available Now, for Those Who Need It Most
For carriers looking to better understand and underwrite wildfire risk, whether in traditional WUI zones or increasingly vulnerable urban neighborhoods, Z-FIRE offers a tested, approved, and field-proven solution. Built on over a decade of confirmed loss data and designed to capture the drivers of urban conflagration, Z-FIRE supports smarter decisions across pricing, underwriting, mitigation, and reinsurance.
Importantly, Z-FIRE is approved for underwriting and rating by Departments of Insurance (DOIs) across all western states, with Oklahoma recently added to the list. Carriers can deploy the model today with confidence, knowing it meets regulatory standards while delivering granular, property-specific insights to support risk selection, pricing, and mitigation strategies.
If you're looking to validate wildfire risk insights on your own book of business, we invite you to put Z-FIRE to the test. Our team can run a targeted evaluation to show how the model performs across your portfolio, highlighting risk segmentation opportunities and identifying properties most vulnerable to structure-to-structure spread.
Get in touch to schedule an evaluation and see how Z-FIRE can strengthen your wildfire strategy today.