Understand how historic wildfires are included in the First Street Wildfire Model to inform the fuels available and potential ignition locations of future wildfires.
Historic wildfires are incorporated in the First Street Wildfire Model to help inform the current status of wildfire fuels and potential ignition locations.
Ignitions
The wildfire behavior model used by the First Street Wildfire Model simulates millions of individual fires under various conditions to estimate risk. Each of these individual fires starts at a location where a historic fire started between 1992 and 2015 and grew to over 100 acres. This data is made public by the United States Department of Agriculture as the Fire Occurrence Database. These locations reflect where human activity, power lines, and lightning strikes have started fires in the past and are likely to again in the future.
Using these probable ignition locations based on historic fires, the model then considers past weather patterns that impact fuels by making them hotter and drier, as well as the type of weather that helps spread fires further such as wind. The building’s location is then used to determine the likelihood of the home being in a wildfire based on how many times the 8 million simulated fires reached it. This allows Fire Factor® to determine risk based on a home’s probability of being in a wildfire, the fire intensity, and the exposure to flying embers.
Fuels
The wildfire hazard estimate is heavily dependent upon estimates of the type, quantity, age, and condition of combustible fuels across the US. Anything that can burn is fuel for a fire. This includes various plants such as grass, shrubs, trees, and dead leaves. As this vegetation piles up, the chance of it burning, or fueling a fire increases.
The U.S. Forest Service (USFS) LANDFIRE fuels dataset is utilized as a baseline, and updated to account for the natural and human-produced disturbances to vegetation which limit the availability of fuels for the development and growth of wildfires. All known disturbances from 2011 to May 2021 were included.
The model also considers a wide variety of weather patterns that impact fuels by making them hotter and drier, as well as the weather conditions that help spread fires further such as high winds and low humidities.
Disturbances
Anything that can burn is fuel for a fire. This includes various plants such as grass, shrubs, trees, and dead leaves. As this vegetation piles up, the chance of it burning, or fueling a fire increases. It is important to understand the natural and human-produced disturbances to vegetation that limit the availability of fuels for the development and growth of wildfires. Data shared by the Monitoring Trends in Burn Severity (MTBS) program was used to account for these disturbances.
After an area was impacted by a wildfire, the amount of fuels available decreases, these would be natural disturbances. To ensure the accuracy of non-wildfire disturbances including harvest, fuel mitigation treatments, prescribed burns, and urban development, they were reviewed by forestry field experts, and validated with remote sensing techniques using satellite imagery. Natural and human-produced disturbances are incorporated into the model to determine where vegetation was modified. This allows the model to ensure any future wildfires in these areas account for changes in the available fuels.
Accounting for fuels in Wildland-Urban areas
The First Street Wildfire Model uniquely considers properties, homes, and businesses within the Wildlands Urban Interface (WUI) to be a burnable fuel type. The WUI is an area of transition, where houses and wildland vegetation meets or intermingle and where wildfires are most pronounced - typically suburban areas that have been extended into and surrounded by wildlands.
To accurately model wildfires risk within the wildland-urban interface (WUI) 550 historic wildfires were analyzed to estimate fuels in these typically suburban neighborhoods.
The Wildfire Model estimates fuels in suburban neighborhoods as a potential source for wildfire spread to other homes from looking at patterns in 550 historic wildfires.
How they were chosen
Fire Factor uniquely estimates wildfire risk to properties, homes, and businesses within the Wildlands Urban Interface (WUI). The WUI is an area of transition, where houses and wildland vegetation meet or intermingle and where wildfires are most pronounced.
Historical fires between 1992 and 2018 that occurred in WUI areas and were greater than 100 acres were selected to differentiate areas where suppression is less likely to occur, from areas where human-caused fires are more likely to occur.