Background

A DC10 Air Tanker is seen over the Woolsey Fire in California. Photo Credit Peter Buschmann

For the first time, U.S. Forest Service Rocky Mountain Research Station and Oregon State University scientists have assessed cross-boundary wildfire exposure in the western United States by mapping potential fire transmission among public and private lands, and identifying areas where ignitions are most likely to expose communities to wildfire. Results are highlighted in the new General Technical Report-392, Cross-boundary Wildfire and Community Exposure: A Framework and Application in the Western US.

The publication’s findings directly support USDA’s shared stewardship initiative that aims to address concerns related to fuel loads, community exposure and cross boundary fires. The results underscore the “all lands” nature of the wildfire problem in the West and helps State, Federal, and local fire planning organizations prioritize strategic forest management activities to reduce wildfire hazards. 

In this example of a cross-boundary fire, an ignition on a national forest (red dot at right) spreads to adjacent landowners and into a community where structures are exposed to the fire.

Research

The cross-boundary assessment relies on fire simulation modeling and identifies specific zones of potential fire exchange between Forest Service lands, other landowners, and communities. The assessment maps 240 million acres where wildfire ignitions can potentially impact over 1,800 communities with significant wildfire exposure.  The communities were ranked in terms of their predicted exposure. Community “firesheds” (meaning the lands surrounding communities where ignitions are likely to cause fires that spread to the urban interface) were mapped for each community and the contribution from different landowners was identified. In this way, communities now have information to understand the scale of wildfire risk and the contributing lands.

Key findings

• These results from a new Forest Service assessment underscore the “all lands” nature of the wildfire problem in the western U.S. and have wide importance to support State, Federal, and local fire planning organizations to prioritize strategic forest management activities to reduce wildfire hazard. 
• There are 240 million acres of forest (public and private owned) in the Western United States where wildfire ignitions can cause fires that will likely spread to the wildland urban interface. 
• National forest lands account for less than 25 percent of the total predicted exposure to western U.S. communities. In other words, 75 percent of fires that occur on national forest land are not predicted to expose communities to wildfire. 
• Over 60% of the total area burned from simulated fires originated from natural ignitions, 40% were human caused.
• On average, one-third of the total area burned for any given landowner is from a fire that ignited elsewhere, i.e. on an adjacent landowner.
• The amount of fire exchange and specifically fire transmission from national forests varied substantially among the 11 western states.