Reducing Fire Threats to Communities

Targeting the Threat

Glowing wildland fireSierra Forest Legacy is working to find long-term solutions to the conflicts that have existed in Sierra Nevada communities for decades. Partnered with our advocacy work, our Fire and Fuels Policy Program is working with public and private agencies to focus on fuel reduction efforts around our communities in order to protect families, homes, and ecosystems of the Sierra Nevada from unnatural wildfire events. Along with the science community, we have long recognized the need to reintroduce fire to the landscape in a way that can help minimize large uncontrolled wildfires and reduce the effect of smoke that these fires have on surrounding communities.

In our effort to restore the Sierra Nevada we have launched our Community Protection Campaign to focus responsible fuels treatments on public lands in the Community Protection Zone. As part of this effort, we have established a strong, supportive voice in local fire safe councils. These councils are active in Butte, Nevada, El Dorado, Calaveras, Placer, and the Tahoe Basin. The purpose of our involvement in the fire safe councils is to work proactively for community fire protection. In our latest effort to help protect the Sierra Nevada, we have adopted the Firewise Communities/USA program.

The Fire Triangle

The fire triangle—fuel, heat, and oxygen— represents the critical factors for combustion. Fires burn and ignitions occur only if a sufficient supply of each factor is present. By characterizing the home as fuel and the heat from flames and firebrands, we can describe a home’s ignitability. An understanding of home ignitability provides a basis for reducing potential WUI fire losses in a more effective and efficient manner than current approaches.

Wildland-Urban Interface

View of forest surrounding homesThe wildland fire threat to homes is commonly termed the wildland-urban interface (WUI) fire problem. This and similar terms (e.g., wildland-urban intermix) refer to an area or location where a wildland fire can potentially ignite homes.

In its simplest terms, the fire interface is any point where the fuel feeding a wildfire changes from natural (wildland) fuel to man-made (urban) fuel. For this to happen, wildland fire must be close enough for its flying brands or flames to contact the flammable parts of the structure.

Community Protection Zone

Surviving house Communities will only feel safe when the land surrounding them - the community protection zone is treated to reduce hazardous fuels through strategic thinning, brush removal, and prescribed burning. Fire and Fuels Scientist Jack Cohen and his colleagues have found that even high intensity crown fires will not directly ignite homes at distances beyond approximately 60 meters (200 feet).

Fire scientists have also determined that mechanical thinning without prescribed fire (including fuel breaks) does not effectively reduce fire behavior under extreme conditions. Their research has concluded that thinning or other mechanical treatments alone will not restore forest ecosystems.

Home Ignition

Recent research provides insights for determining the vegetation clearance required for reducing home ignitions. Structure ignition modeling, fire experiments, and WUI fire case studies provide a consistent indication of the fuel and heat required for home ignitions. Federal fire scientists have determined that it is the home and its immediate surroundings (30m-60m) that principally determine the potential for home ignition during fires (Cohen, 2000).

Firewise landscape around homeAn understanding of home ignition potential provides a basis for understanding the wildfire threat to homes, and thus leads to reducing potential WUI fire losses. A wildland fire does not spread to homes unless the homes meet the fuel and heat requirements sufficient for ignition and continued combustion. Similarly, the flammables adjacent to a home can be managed with the home's materials and design chosen to minimize potential firebrand ignitions. This can occur regardless of how intensely or fast spreading other fires are burning. Reducing WUI fire losses must involve a reduction in the flammability of the home (fuel) in relation to its potential severe-case exposure from flames and firebrands (heat).

Fire Research Relating to Reduction of Threats to Communities

Calkin, D.E., Cohen, J.D., Finney, M.A., Thompson, M.P. (2014) How risk management can prevent future wildfire disasters in the wildland-urban interface. PNAS,  Vol.111:2 (687 KB PDF)

Cohen, J.D. 1999. Reducing the Wildland Fire Threat to Homes: Where and How Much? U.S. Forest Service, Gen. Tech. Rep. PSW-GTR-173 (434KB PDF)

Cohen, J.D. 2000. What is the Wildland Fire Threat to Homes? U.S. Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory. Missoula, MT, Presented at Northern Arizona University, School of Forestry, Thompson Memorial Lecture Series (361KB PDF)

Cohen, J. 2008. The Wildland-Urban Interface Fire Problem--A consequence of the fire exclusion paradigm. Forest History Today. Fall 2008 (1.2 MB PDF)

Mutch, R.W. et al. 2010. Protecting Lives and Property in the Wildland–Urban Interface: Communities in Montana and Southern California Adopt Australian Paradigm. Fire Technology. DOI: 10.1007/s10694-010-0171-z. (453 KB PDF)

Reinhardt, E.D., R.E. Keane, D.E. Calkin, and J.D. Cohen. 2008. Objectives and considerations for wildland fuel treatment in forested ecosystems of the interior western United States. Forest Ecology and Management 256:1997-2006. (191 KB PDF)

Read more Fire Science research literature here.

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