AIR Worldwide (AIR), a Catastrophe risk modeling firm, has released an updated Wildfire Model for the United States, featuring a catalog of fire clusters and a historical event set that features 17 events, including the 2017 Tubbs/Atlas and Thomas fires in California.
The model is designed to assess the risk of wildfire to property within the 13 westernmost conterminous states. In California, the risk assessment shows 15% of California homes at risk. The Top 5 counties where homes are at risk are in Northern California.
The event-based modeling approach accounts for the variability in weather in the current climate regime and its impact on fire behavior, enabling the model to simulate correlated countrywide wildfire activity.
AIR assesses “potential insured losses from wildfire throughout the insurance and risk transfer value chain,” said Dr. Jayanta Guin, executive vice president of AIR Worldwide. “AIR is building on our experience in modeling wildfires by introducing a fresh approach to estimating the hazard on both local and national levels and accounting for the full range of vulnerabilities in residential, commercial, and industrial lines of business.”
The model features a catalog of fire clusters with each cluster consisting of fires ignited within 150 miles of one another over a period of seven days. AIR uses historical fire data to characterize fire behavior in different ecological regions of North America, known as ecoprovinces, and uses spread models to create stochastic fires for each of these regions.
“With residential and commercial development continuing to increase in areas prone to wildfire risk, the model explicitly accounts for this increased penetration into the WUI [wildland-urban interface],” said Tammy Viggato, senior scientist at AIR. “Approximately one-third of the U.S. population currently lives in the WUI in the United States, where most wildfire-related losses occur, and this figure continues to grow rapidly. To address the increasing risk, the model realistically captures fire behavior as it moves from rural areas to the suburbs and, under extreme conditions, into more urban areas.”
The wildfire model simulates the probability of fires spreading into areas based on wind speed and direction, availability of fuels, terrain, and likelihood of suppression. It also accounts for the ways fires spread, including fire branding and spotting. The model calculates flame length at each time step, which correlates with the intensity of the fire, and is used to estimate the severity of its damage.
Based on these criteria, in conjunction with constantly evolving wind conditions and suppression efforts, the model can determine how and where the fire may progress across the landscape.