Methods
Wildfire Risk to Communities is built from nationally consistent data and uses the best available science. The interdisciplinary team behind Wildfire Risk to Communities includes national experts in wildfire risk, fire behavior modeling, wildfire mitigation, and socioeconomic trends.
Wildfire Risk Data & Methods
The wildfire risk data found in the Explore section of Wildfire Risk to Communities is based on the best available science and nationally consistent data about vegetation and fire-behavior fuel models, topography, recent weather patterns, and long-term simulations of large wildfire behavior. It is based on techniques developed by the Missoula Fire Sciences Laboratory of the Rocky Mountain Research Station and Pyrologix, a Vibrant Planet company.
For more details about the input data and modeling methods read Technical Papers in the Download section.
Low, medium, high, and very high risk categories
When you first view the page for your selected community, county, tribal area, or state in the Explore section, you will see several colorful labels showing low, medium, high, or very high risk categories. These categories are determined by the following rules.
Summary Statement
Data source: Risk to homes, national percentile rank.
- Low: <40th percentile
- Medium: >40th and <70th percentile
- High: >70th and <90th percentile
- Very High: >90th percentile
Risk to Homes
Data source: Risk to homes, national percentile rank.
- Low: <40th percentile
- Medium: >40th and <70th percentile
- High: >70th and <90th percentile
- Very High: >90th percentile
Wildfire Likelihood
Data source: Wildfire likelihood, national percentile rank.
- Low: <40th percentile
- Medium: >40th and <70th percentile
- High: >70th and <90th percentile
- Very High: >90th percentile
Risk Reduction Zones
Data source: Fraction of buildings exposed (indirectly or directly exposed).
For communities:
- Low: <10%
- Medium: >10% and <40%
- High: >99% <100%
- Very High: 100%
For counties and tribal areas:
- Low: <40%
- Medium: >40% and <75%
- High: >75% and <99%
- Very High: >99%
For states:
- Low: <33% of communities in the state rank “Medium” or higher.
- Medium: >33% of communities in the state rank as “Medium” and <33% rank “High” or “Very High”; or more than 1,500,000 buildings are exposed.
- High: >33% of communities in the state rank as “High” and <33% rank “Very High”; or more than 3,500,000 buildings are exposed.
- Very High: >33% of communities in the state rank as “Very High”; or more than 5,000,000 buildings are exposed.
Vulnerable Populations
Data source: Percent of census tracts where top 2 criteria exceed the community median. (See more in the Vulnerable Populations section below.)
- Low: 0%
- Medium: >0% and <33%
- High: >33% and <50%
- Very High: >50%
Vulnerable Population Data & Methods
Data about potentially vulnerable populations found in the Explore section of Wildfire Risk to Communities are from the U.S. Census Bureau’s American Community Survey (ACS). Data shown in the browser window are from the five-year rolling survey period representing 2019-2023. The timing of ACS updates may differ between the data shown in the browser and data in the downloadable report.
How we measure “local rank.” When you first view data about potentially vulnerable populations in the Explore section, the list is sorted by local rank. (By “local” we mean the selected community, county, tribal area, or state.) This is done by ranking all eight variables against all other locations in the United States. By default, only the two highest-ranked variables are checked, but users can adjust the map by checking and unchecking variables.
When a variable is checked on, it shows the census tracts that are greater than or equal to the local median.
Human-Caused Wildfires Data & Methods
Data in the interactive visualization “Human-Caused Wildfires” (found on the page Prevent Ignitions) are from the USDA Forest Service’s Fire Occurrence Database (FOD). Wildfires with no known cause are excluded.
Wildfires are recorded in the FOD as point data and summarized in the visualization to the county level. However, wildfires can cross county boundaries, and the point recorded in the FOD may not reflect the county/counties most impacted by an ignition. Wildfires are also recorded by the date they were discovered, and some wildfires can go for days before being noticed.
Other organizations, including the National Geographic Area Coordination Center managed by the National Interagency Fire Center, also monitor human-caused ignitions. Although some discrepancies exist between data sources, the total share of human-caused ignitions is generally consistent across different data sources when summed to state or national levels.
See the USDA Research Data Archive for complete information about this data source and methods.
If you use data from this visualization, please cite it as follows:
Short, Karen C. 2022. Spatial wildfire occurrence data for the United States, 1992-2020 [FPA_FOD_20221014]. 6th Edition. Fort Collins, CO: Forest Service Research Data Archive. https://doi.org/10.2737/RDS-2013-0009.6. As reported at wildfirerisk.org/preventignitions.
Release Notes
May 2025
In May 2025, updates were made to reflect the latest data from the U.S. Census Bureau. These updates include the searchable list of communities, Tribal areas and counties; the community boundaries shown on the maps; and data under “Vulnerable Populations.” More information about the vintage and data sources can be found in the FAQ, “What time period do the data reflect?“
December 2024
New features were added in December 2024 that make the site easier to navigate, help users interpret wildfire risk data, and enhance accessibility for users with disabilities. The improvements were developed in response to user testing and feedback.
May 2024
A comprehensive update to all data was completed in May 2024, including new and improved wildfire risk data, updated vulnerable populations data, and an updated list of searchable locations. In the Explore section, the “Exposure Type” page was replaced with a new “Risk Reduction Zone” page. Wildfire data on the “Risk to Homes” and “Wildfire Likelihood” tabs in the Explore section were summarized to a new Risk Calculation Area, which includes a 2.4 km buffer around communities. Other improvements included a new basemap with more reference locations and a new page about “Funding” in the Reduce Risk section.
February 2024
In February 2024, an interactive dashboard was added to the website to support applicants to the Slip-On Tanker Grant program. An accompanying page provided answers to Frequently Asked Questions about the dashboard and data.
May 2023
In May 2023, an interactive dashboard was added to the website to support applicants to the Community Wildfire Defense Grant program. An accompanying page provided answers to Frequently Asked Questions about the dashboard and data.
March 2023
Major user interface improvements were launched in March 2023, including an overview page for each searched location. The “Vulnerable Populations” section was redesigned to include interactive, census-tract scale maps of social vulnerability with new variables and a downloadable report.
The Reduce Risk section was reorganized, and two new pages were added: “Smoke Ready” and “Equitable Risk Reduction.” An interactive data visualization of human-caused ignitions was added to the Prevent Ignitions section.
August 2022
The August 2022 update of Wildfire Risk to Communities included two important features. First, tribal areas were added to the search. Second, data under “Vulnerable Populations” was updated to reflect the latest data from the U.S. Census Bureau’s American Community Survey. Data to support the Community Wildfire Defense Grant program was added to the “Download” section.
April 2021
In April 2021, new data was added to Wildfire Risk to Communities. The update featured the ability to view “expanded areas” for communities, allowing users to see risk in populated areas outside of official community boundaries. The tool was also expanded to allow comparisons with other communities in the nation (instead of just at the state level).
April 2020
The first version of Wildfire Risk to Communities was launched in April 2020. It was the first time wildfire risk to communities has been mapped nationwide and included information to help communities understand, explore, and reduce wildfire risk.