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Wildfire exposure in the western US

Community and cross-boundary wildfire exposure in the western US

Predicting wildfire disasters presents a major challenge to the field of risk science, especially when fires are propagated over long distances through diverse fuel types and complex terrain. A good example is in the Western US were large tracts of public lands routinely experience large fires that spread from remote wildlands into developed areas and cause substantial structure loss and frequently fatalities as well. In this project we provide the first comprehensive assessment of where public wildlands in the Western US potentially contribute wildfire exposure to communities in the 11 western US states and provide a framework for assessing cross-boundary wildfire exposure and a case study application in the western US. The case study provides detailed mapping and tabular decision support in web portals 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 Undersecretary Hubbard to assess community wildfire risk specifically from Forest Service lands, and newer shared stewardship initiatives.

Existing risk assessment technologies and frameworks do not explicitly examine the cross-boundary problem intrinsic to community wildfire risk from large public wildlands since they measure in-situ risk without specifying linkage to ignition origin or fire spread through land to developed areas. As fires get larger and larger, linking human and natural values to the wildlands that propagate fires becomes increasingly important. In particular, the risk assessment process used by state agencies in the US and implemented in Wildfire Risk Assessment Portals (WRAPs) for each of the 17 western states could be enhanced with newer methods to consider cross-boundary risk and exposure metrics. These risk assessments use pixel-level indices to measure community exposure to wildfire, ignoring large fire spread in the surrounding wildlands. By contrast, the newer assessment methods developed by Forest Service researchers use large fire simulation but lack frameworks to explicitly measure and map cross-boundary and wildland-community wildfire transmission. Neither ad hoc nor published definitions of community wildfire protection areas account for the geography and scale of risk to communities Science reviews also lack discussion of cross-boundary fire and measurement of community wildfire risk. Clearly, in an era where the scale of risk is rapidly expanding with larger and larger fires, it is important to understand the topological properties of cross-boundary fire on landscapes in the US and elsewhere that are fragmented by ownerships, management intent and fire management jurisdictions. In this work we use outputs from the FSim model to develop and apply a framework for assessing cross-boundary and community wildfire exposure.

How many communities are potentially affected by future wildfires? 

  • We estimate a total of 1,812 communities in the western US could be significantly impacted by future wildfires (“significant” is defined as > 1 structure per year on average).
  • Ignitions on national forest lands will likely affect 516 of these 1,812 communities (> 1 structure per year on average).
  • For comparison, Paradise CA ranked 189th out of the 1,812 communities exposed to all fires in the western US.

How many structures in these communities are exposed by wildfires?

  • We estimate ignitions on all lands will expose 19,400 structures to wildfire per year on average. The modeling estimates structure exposure from wildland fires, not structure to structure fire within communities.
  • Of the total exposure, ignitions on national forest lands will expose an estimated 4,000 structures (21% of total) in the western US per year on average.
  • Due to administrative restrictions on national forest lands, only about half of this exposure (2,200 structures) originates on lands where mechanical treatments can be conducted.

How large are the community firesheds, i.e. the source area for wildfires that expose communities?

  • There are an estimated 240 million acres in the western US where fire ignitions are likely to expose communities to wildfire.
  • There are an estimated 57 million acres on western national forests where fire ignitions are likely to expose communities. This amounts to 41% of the national forest land in the western US.
  • Of the 57 million acres of national forest land where fire ignitions are likely to expose communities, due to administrative restrictions 34 million acres are available for mechanical treatment (60%).

The products from this research are being used in the Scenario Investment Planning Platform to understand where fuel management can be leveraged to reduce cross boundary and community risk. The following graphics are Wildfire exposure to the wildland urban interface in the western US.

Image: Top 50 communities exposed to wildfire

Top 50 communities exposed to wildfire in the western US by ignition source. Dot size indicates the magnitude of exposure to each community from each national forest.

This figure is taken from: Ager, A.A., Palaiologou, P., Evers, C., Day, M.A., Ringo, C., Short, K.C., 2019. Wildfire exposure to the wildland urban interface in the western US. Applied Geography 111, 102059.

Image: Structure exposure

Structure exposure for the 11 western US states from wildfires ignited on national forest land based on management capacity.Structure exposure is measured as the annual predicted structures affected using simulation outputs.

Image: National forest land causing structure exposure to communities in the 11 western US states.

National forest land causing structure exposure to communities in the 11 western US states. Data filtered to show exposure ≥ 1 structures per year (fireshed). Areas of the fireshed that are available for mechanical treatments (manageable), are fire adapted and have forested fuel models are show in blue.

Modified: Nov 18, 2019

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Ager, Alan A.; Day, Michelle A.; Palaiologou, Palaiologos; Houtman, Rachel M.; Ringo, Chris; Evers, Cody R. 2019. Cross-boundary wildfire and community exposure: A framework and application in the western U.S. Gen. Tech. Rep. RMRS-GTR-392. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 36 p.

Ager, Alan & Palaiologou, Palaiologos & Evers, Cody & Day, Michelle & Ringo, Chris & Short, Karen. (2019). Wildfire exposure to the wildland urban interface in the western US. Applied Geography. 111. 102059. 10.1016/j.apgeog.2019.102059.

Evers, C., A. A. Ager, M. Nielsen-Pincus, P. Palaiologou, and K. Bunzel. 2019. Archetypes of community wildfire exposure from national forests of the Western US. Landscape and Urban Planning 182:55-66.

Palaiologou, P., A. A. Ager, M. A. Day, R. Houtman, and A. M. G. Barros. 2019. Fine-scale assessment of cross-boundary wildfire events in the western United States. Natural Hazards in Earth System Science 19:1755-1777.

Palaiologou, P., A. A. Ager, M. Nielsen-Pincus, C. Evers, and M. Day. 2019. Social vulnerability to large wildfires in the western USA. Landscape and Urban Planning 189:99-116.

Ager, A. A., P. Palaiologou, C. R. Evers, M. A. Day, and A. M. G. Barros. 2018. Assessing transboundary wildfire exposure in the southwestern United States. Risk Analysis 38:2105-2127.

Day, M. A., A. A. Ager, P. Palaiologou, and C. Ringo. 2018. Cross-boundary wildfire transmission in Oregon -- A quantitative transmission analysis. Final report to the Oregon Department of Forestry, USDA Forest Service, Rocky Mountain Research Station, National Fire Decision Support Center.

Ager, A. A., C. Evers, M. A. Day, H. K. Preisler, A. M. G. Barros, and M. Nielsen-Pincus. 2017. Network analysis of wildfire transmission and implications for risk governance. PLoS ONE 12: e0172867. doi: 10.1371/journal.pone.0172867