Guiding preventative wildland fire mitigation policy and decisions with an economic modeling system
Introduction
Residential developments in western US unincorporated areas adjacent to public lands have expanded substantially in recent years (Stein et al., 2005, Stein et al., 2007, NFAEB (National Fire and Aviation Executive Board), 2005, US Census Bureau, 2001), raising a series of questions for land managers and planners. What actions should be taken to reduce wildfire risk to homes in the Wildland Urban Interface (WUI)? How can residents and fire suppression organizations reduce the costs of fighting fire? How does structure protection fit into a broader picture of public land management, including demands to sustain fire-adapted ecosystems? This research examines one of the most salient questions regarding human developments in areas with high levels of wildfire occurrence: How can individual homeowners and the public most effectively allocate available financial resources to protect residential WUI structures from wildland fire? By linking models of structure ignition and wildfire probability in the most common forest type surrounding western WUI developments, this research examines the cost effectiveness of various preventative mitigation measures to protect structures from wildland fire.
Implementation of the two most common approaches to reduce wildfire risk – Firewise activities, and thinning and prescribed burning silvicultural treatments – was modeled for a study area in the Bitterroot Valley of western Montana. Firewise mitigation efforts are actions taken to modify the residence itself as well as fuel conversions within the home ignition zone (HIZ). The HIZ was defined by Cohen (2001) as the area that principally determines the home ignition potential. The HIZ includes the home, its exterior materials and design, and the area around the home typically within 30.5 to 61 m (100 to 200 ft) (Cohen, 2001). In this study, the HIZ is defined as the area extending 30.5 m (100 ft) from each side of each structure. Firewise mitigations may be restricted by cost, ownership boundaries in the HIZ, action or inaction by adjacent landowners, subdivision covenants, and tradeoffs with other values provided by fuels, such as shade, wildlife habitat and privacy. Silvicultural treatments in the forest and grassland areas surrounding residences are intended to modify the behavior of a wildfire within and adjacent to the HIZ treated areas and are generally considered the responsibility of public land management agencies funded mainly with tax revenues.
Forest managers and researchers observe that population expansion and fire protection activities have substantially modified fire regimes in the high fire frequency landscapes of the western U.S. (Romme et al., 2003, Swetnam et al., 1999, Arno et al., 1997, Covington and Moore, 1994). Many authors note how fire management policies preventing low intensity fire in dry ponderosa pine (Pinus ponderosa) landscapes have, ironically, increased the long-term threat of dangerous crown fire and associated home loss (Brose and Wade, 2002, Taylor and Skinner, 1998, Quigley et al., 1996, Agee, 1993, Agee, 1994, Arno, 1980).
Extreme fire behavior, partially attributable to a century of fire-exclusion, has already collided with many human communities nestled in and around flammable forests in the wildland urban interface (WUI), resulting in increasing home losses to wildland fires in recent years. Despite these losses, an increasing number of homes are being built in low elevation ponderosa pine forested areas in unincorporated places in the western US that often have limited fire protection resources (Stein et al., 2007, Stein et al., 2005, NFAEB (National Fire and Aviation Executive Board), 2005). Hedonic pricing model research suggests that homes in close proximity to forested areas are highly desirable (Kim and Johnson, 2002), indicating a sustained demand for houses in the WUI and the likelihood of increasing development. However, Loomis (2004) identified reduced housing value due to proximity of recent fire and Donovan et al. (2007) demonstrated that housing values decreased following heightened awareness of high wildfire risk.
The proximity of houses to flammable forests places them at risk of ignition. Structure ignitions from forest wildfires occur through several vectors of heat transfer. Large wildland fires produce firebrands that can reach a house from more than a mile away (Albini, 1983). Fires approaching a structure can also affect wind and temperature factors that impact the radiant and convective heat fluxes, all affecting ignition risk. Therefore, home ignition probability varies at the home ignition zone scale (Cohen and Butler, 1998).
Table 1 indicates that during the period 2000–2007, annual US wildland fire suppression costs were roughly $1 billion and hundreds of primary residences were destroyed annually by wildland fire. During 2003 alone, wildland fires burned 4090 primary residences in the US, mainly in fires near San Diego, California. Resident and firefighter lives have been lost to wildland fires that destroy WUI homes. Fire hazard is expected to remain stable or grow in these areas, thus compounding the risk to lives and homes. Recent research on climate change suggests higher temperatures and longer summers may elevate North America's annual forest fire acreage (Westerling et al., 2006). With continued growth of the WUI and increasing fire hazard, the number of WUI residences threatened each year by wildland fire and inflation-adjusted wildland fire suppression expenditures devoted to defending these structures will likely continue to rise.
Wildland fire suppression is a dangerous, expensive activity undertaken for myriad reasons other than simply the protection of homes. Other protection considerations include critical infrastructure, sensitive wildlife habitat, soil productivity, aesthetics, and air quality (Graham et al., 2004, Cohen and Stratton, 2003, Kalabokidis et al., 2002, Conrad et al., 2001, Tiedemann et al., 2000, Swetnam et al., 1999, Covington et al, 1997, Fulé et al., 1997, Covington and Moore, 1994, Reynolds et al., 1992, Weaver, 1943). Yet not all fires can or should be suppressed, as there are many benefits derived from wildland fire. Ecosystems rely on the wildland fire process, as do human communities, since frequent low intensity fire reduces woody fuels and the types of fires that may cause widespread structure loss. Although the benefits of fire are well recognized, rural residents and their property are simultaneously threatened by fire, creating an ongoing social dilemma on the extent of costly suppression activities. The range of risk-reduction strategies must be carefully evaluated with criteria including efficiency and effectiveness, to which this study is intended to make a contribution.
Section snippets
Area description
We applied a cost-effectiveness analysis (CEA) of preventative mitigation strategies to a case study area in the Bitterroot Valley of western Montana, US. Of the 136,945 ha (338,400 ac) within the study area, roughly 70% is forest, 11% is shrub land, and 8% is grass land. The residential area is a subset of this landscape, covering 550 ha (1360 ac) with 291 WUI residences. The composition of the vegetative communities in the residential area is roughly 38% forest, 24% shrub land, 37% grass land,
Methods
The overall cost-effectiveness evaluation can be distilled into three steps: (1) a baseline wildfire structure ignition hazard calculated as the average product of a baseline wildland fire probability at each house and a baseline ignition probability given exposure to wildland fire for each house; (2) estimation of modified home ignition hazard probabilities following the implementation of mutually exclusive HIZ or mechanical and prescribed fire mitigation options for seven expenditure levels;
Existing probability of home ignition
SIMPPLLE modeling revealed that the existing probability that polygons hosting houses in the study area will experience wildland fire during the period 2005–2034 is extremely low. The 30-year wildland fire probabilities for individual homes ranged from 0.0 to 0.0496 for these polygons, with 201 homes having a zero probability.
Although few study area houses are expected to face a wildland fire between 2005 and 2034, SIAM modeling for the 39 homes visited revealed that only three residential
Discusssion
The large range in predicted cost-effectiveness ratios for all mitigation options suggests that economic analysis can provide useful information to support wildfire mitigation planning. The findings in this case study, suggest that most of the HIZ mitigation options have superior performance over silvicultural forest treatments when compared for seven expenditure levels ranging from $184,000 to $5,604,048. Given limited budgets to address the problem of WUI structure protection; this is exactly
Conclusion
This study has pioneered a technique that combines wildfire probability with structure ignition probability given a passing wildfire to conduct a cost-effectiveness analysis of preventative home ignition mitigation options. The study demonstrates the utility of cost-effectiveness analysis to help guide mitigation efforts in low elevation communities across the western US. The case study area in the Bitterroot Valley, Montana, revealed that, for the particular expenditure levels examined, most
Acknowledgments
The opinions expressed herein are those of the authors and do not necessarily represent the official position or policies of the USDA Forest Service. Funding for this study was obtained through the McIntire–Stennis grant program, as well as through the Missoula Firelab. The authors would like to recognize the many colleagues that helped design and execute the study as well as anonymous study participants who allowed visits to and modeling of their homes. Dr. Ronald Wakimoto, Dr. Thomas Power,
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