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Wildfire Threats

Wildland fire and related natural disturbances continue to grow as a major global threat to property, lives, and ecosystems. There is growing scientific evidence that climate change is in part responsible for catastrophic fire events that are increasingly common.

A dramatic increase in the urban interface across much of the United States has exacerbated the problem. Fire suppression costs continue to spiral, and each year brings new records in area burned by extreme wildfires that less resemble the natural fire regimes in the broad expanse of fire-adapted ecosystems. Wildfires increase the likelihood of a wide range of adverse impacts on wildlands, including flooding, erosion, loss of key wildlife habitat, and other ecological and economic values.

Threat Interactions

Wildland fire interacts with many other disturbance agents at multiple scales over space and time. For example, bark beetle and wildfire form a particularly intricate disturbance complex. Bark beetle infestations and wildfire were historically dominant influences on successional processes over large areas in the Western United States. In general, frequent, low-severity fires maintained stand densities and fuels, and bark beetles attacked patches of mature trees weakened by fire, disease, or other factors. These stand dynamics caused patchy, cyclic mortality and an equilibrium age-class distribution at the landscape scale. Climate change, fire suppression, and other management over the past 100 years have altered succession and disturbance regimes, and created forest conditions that are prone to both severe wildfire and bark beetle outbreaks.

From a management perspective, a clear understanding of the bark beetle–fire relationship is needed to formulate strategies to dampen the disturbance process. As federal land management agencies accelerate treatment of hazardous fuels over wide areas in the Western United States, practices such as mechanical thinning, surface fuel reduction, the reintroduction of prescribed fire, and natural fire will likely change bark beetle dynamics and bark beetle-caused tree mortality. For instance, treatments may reduce stand-scale susceptibility to beetle infestation by reducing stand density, increasing tree vigor, and removing weakened “focus” trees. However, site disturbance, wounding, and mortality from mechanical or prescribed fire treatments may create more “focus” trees, which act as magnets for bark beetles. Further, prescribed fire and thinning prescriptions in the dry forest types favor retention of tree species such as ponderosa pine (Pinus ponderosa) that are hosts for a suite of bark beetles (including mountain pine beetle, Dendroctonus ponderosae, western pine beetle, D. brevicomis, and engraver beetles, Ips spp.), potentially leading to increased mortality if an outbreak occurs. This particular threat complex is one of many wildland fire disturbance interactions of concern to land managers.

 

Other Links and Tools—The Science and Technology of Wildfire Risk Assessment

A major effort is underway in multiple federal agencies to develop the science of wildfire risk assessment as a means to minimize wildfire impacts and predict occurrence. Wildfire risk assessment efforts span a range of temporal scales from the day-to-day prediction of wildfire occurrence to long-term strategic planning where mitigation options are analyzed over years and even decades. Some examples of online content concerning these areas are provided below.

Current Wildfire Activity

Detailed information on current wildfire activity in the United States can be found at the Incident Information System.

Current Wildfire Potential

A comprehensive information source that provides a national view of current weather and fire potential, including national fire danger and weather maps and satellite-derived "greenness" maps is available at the Wildland Fire Assessment System (WFAS). The system was first made available in 1994. In 1999, operation was transferred from the Fire Sciences Laboratory (FS Rocky Mountain Research Station, Missoula MT) to the National Interagency Fire Center (NIFC, Boise, ID).

The Wildland Fire Assessment System Web site provides national maps on three components: fire potential/danger, weather, and moisture/drought. The fire danger rating system is a comprehensive index that takes into account current and antecedent weather, fuel types, and both live and dead fuel moisture

The WFAS is currently based on weather observations taken at fire weather stations throughout the United States and entered into the Weather Information Management System (WIMS). National Fire Danger Rating System (NFDRS) calculations are done at the National Computer Center at Kansas City (NCC-KC). The fuel model, index, and fire danger levels are set by local managers. National WFAS maps are produced from fire danger levels using simple inverse distance square interpolation. Satellite "greenness" products are currently stand-alone indicators of fire potential and not integrated into the calculations except in the experimental projects.

Strategic Wildfire Risk Assessment at the Regional Scale

A number of strategic wildfire risk assessment systems have been built at the state and regional levels in the United States. An example of an interactive online wildfire risk mapping program is the California fire and Resource Assessment Program

An example toolkit for homeowners and others to assess wildfire risk can be found at
The Southern Wildfire Risk Assessment (SWRA,) a multiagency comprehensive assessment that was initiated by the Southern Group of State Foresters. The SWRA relies on multiple geographic information system (GIS) layers that can be combined to map wildfire risk. The SWRA uses a numerical weighting scheme to generate outputs of overall risk.

Wildfire Modeling Software

Wildfire risk assessments rely on wildfire behavior models that predict wildfire spread and intensity as a function of fuels, weather, topography, and other factors. A comprehensive site of wildfire modeling software can be found at www.fire.org. Many of these programs are used in wildfire risk assessments.

WWETAC Projects—Wildfire Risk Assessment at WWETAC

The Center’s efforts to date have focused on tools and a framework for wildfire risk assessment to meet the needs of fuel management planners in federal land management agencies. Widespread fuel reduction programs have been initiated in many parts of the United States as part of the National Fire Plan and the Healthy Forest Restoration Act. Developing effective mitigation strategies is a challenging problem, especially on vast tracts of federally managed wildlands in the Western United States. Fuel reduction activities on Federal lands are generally difficult to plan and implement owning to cost, public expectations, and land management regulations. State-of-the-art wildfire modeling is frequently required to demonstrate the benefits of fuel reduction treatments and defend fuel management projects. Designing and testing fuel treatment scenarios is complex, and many metrics, including fire spread, intensity, expected loss, and other ecological risks must be analyzed. The problem is compounded by poor data integration among fire behavior models, desktop GIS, and Forest Service corporate data.

At the center we have been working on streamlining the fuel treatment management process. One of these efforts resulted in ArcFuels, a GIS interface. ArcFuels provides the following key functionality for fuels treatment planning:

1. An interactive system within ArcMap to develop stand-specific silvicultural prescriptions and fuel treatments within the Forest Vegetation Simulator (FVS, Dixon 2003), including thinning, underburning, and mechanical fuels treatment.
2. Automated generation of data plots showing how stand fuel treatments change wildfires in terms of flame length, fire behavior, and stand mortality over time.
3. Rapid scale-up of stand-specific treatments to simulate landscape-wide changes in vegetation and fuels from proposed management activities.
4. Tight data linkages to FlamMap or FARSITE to simulate landscape-scale fire behavior and measure the treatment performance in terms of wildfire probabilities, spread rates, and fireline intensity (Finney 2004).
5. Ability to easily modify and re-evaluate fuel treatment scenarios.
6. Integration of fire modeling spatial outputs into ArcGIS and other programs to facilitate the evaluation of fuel treatments with multiresource objectives.

Dixon, G.E. 2003. Essential FVS: A user's guide to the forest vegetation simulator. USDA Forest Service, Internal Rep., Forest Management Service Center, Fort Collins, CO.

Finney, M. A. 2004. FARSITE: Fire area simulator- Model Development and Evaluation. USDA Forest Service, Rocky Mountain Research Station, RMRS-RP-4.

More Information on ArcFuels