Cross-boundary wildfire and community exposure: A framework and application in the western U.S.

In this report we provide a framework for assessing cross-boundary wildfire exposure and a case study application in the western U.S. The case study provides detailed mapping and tabular decision support materials for prioritizing fuel management investments aimed at reducing wildfire exposure to communities located proximal to national forests. The work was motivated by a number of factors, including a request from U.S. Department of Agriculture Undersecretary James Hubbard (Natural Resources and Environment) to assess community wildfire risk specifically from Forest Service lands, language in the 2018 omnibus bill (Public Law 115-141) calling for a national assessment of wildfire risk to communities, and newer shared stewardship initiatives (Clavet 2018). We used national FSim simulation outputs to (1) estimate cross-boundary wildfire among major land types (Federal, State, private); (2) quantify structure exposure to all western communities; (3) map sources of community wildfire exposure (firesheds); (4) characterize firesheds in terms of management opportunity and fuels; and (5) prioritize communities based on integration of exposure and fireshed characteristics. The study revealed that 1,812 communities in the western U.S. could potentially be significantly impacted by future wildfires (more than 1 structure per year on average). Ignitions on national forest lands will most likely affect 516 of these 1,812 communities (more than one structure per year on average). Of the total exposure, ignitions on national forest lands will expose an estimated 4,000 structures (21 percent of total) in the western U.S. per year on average. Due to administrative restrictions on national forest lands, only about half of the total exposure from national forest lands (2,200 structures) originates on lands where mechanical treatments and prescribed fire are either allowed or ecologically appropriate. The framework can guide future efforts aimed at quantifying community and other cross-boundary exposure situations, and the outputs can be used to help identify shared stewardship projects, and prioritize fuel and other management activities within public land management agencies.