5th Symposium on Fire and Forest Meteorology and the 2nd International Wildland Fire Ecology and Fire Management Congress

Monday, 17 November 2003: 4:30 PM
Fire Potential Rating for Wildland Fuelbeds
David V. Sandberg, USDA Forest Service, Corvallis, OR
Poster PDF (157.8 kB)
The Fuelbed Characteristic Classification System, or FCCS, (Sandberg and Ottmar 2002) is a systematic catalog of inherent physical properties of any wildland fuelbed. FCCS is designed to provide the best possible fuel estimates and potential fire parameters based on as much or as little site-specific information as is available. The detailed fuel estimates are needed to support fire hazard assessments and fuel treatment decisions, as well as other research initiatives. The FCCS will provide these detailed estimates based on either specific fuel data (types of fuel and their relative abundance) or general site data that are available for broader areas (such as Ecoregion Division, vegetation form, cover type, or other data obtained from remote sensing, forest inventories, or models). The system will also accept a mixture of both types of data.

FCCS is comprised of 1) A large database of physical parameters that describe the size, abundance, physical character, and arrangement of the several dozen components that comprise a wildland fuelbed; compartmentalized by vertical position from forest canopy, shrub vegetation, low vegetation, woody fuels, litter, and moss/duff strata. The prototype FCCS database includes 200+ fuelbeds common to North America, and a process has been established to add several tens of thousands more fuelbeds in the next several years. 2) An expert system to interactively select fuelbed from general site data and to adjust fuelbeds in the database based on specific site data or other information available to the user. This component of the system also calculates and summarizes fuelbed properties by vertical strata, and used a set of look-up tables to assign properties based on vegetation species or physiognomic character. 3) Calculation of relative (normalized to a scale of 0-10) Fuelbed Fire Potentials, i.e. the intrinsic capacity of a fuelbed for surface fire behavior, crowning potential, and fuel consumption. These potentials are calculated from the loading, heat content, bulk density, and characteristic thickness of fuel elements without consideration of moisture content or environmental conditions. Essentially, they represent the potential fire behavior and effects of an oven-dry fuelbed with no wind or slope influence.

FCCS calculates and reports nine Fire Potentials for every fuelbed, arranges in three categories:

Fire Behavior Potential, consisting of a user-defined combination of three component potentials:

RP, or Reaction Potential, that represents the approximate reaction intensity (energy release per unit area per unit time) and is a function of fuel surface area per unit of ground surface, depth of the surface fuelbed stratum, heat of combustion, and a scaling factor based on flammability.

SP, or Spread Potential, proportional to the no-wind rate of spread in surface fuels (distance per unit time), and is a function of Reaction Potential and the abundance of very fine (less than 1 mm diameter) fuels.

FP, or Flame Length Potential, proportional to fireline intensity or flame length and derived from the product of Reaction Potential and Spread Potential.

Crown Fire Potential, which is a rule-based ranking of crown fire potential based on admittedly poor scientific understanding of the factors that control torching and crowning, based on:

TC, or Torching Potential, is a heuristic that rates the potential for crown involvement based on the Flame Length Potential related to the physical gap distance between the surface and crown fuel strata. DC, or Dependent Crown Fire Potential, a heuristic based on Torching Potential, canopy dimensions, and crown cover.

IC, or Independent Crown Fire Potential, another heuristic similar to Dependent Crown Fire Potential, but with higher thresholds of crown cover.

Available Fuel Potential, which is only the fuel loading of all fuel elements within a set depth from the surface of the fuel component, intended to approximate the combustible biomass under oven-dry moisture conditions in each of three stages of combustion:

FA, or Flame Available Fuel, the sum of mass within one-half inch (12.7 mm) of the surface. SA, or Smoldering Available Fuel, mass between and 2 inches (51 mm) of a surface, and RA, or Residual Available Fuel, the mass between 2 and 4 inches (100mm) of a surface.

Fire Potential are a set of relative values that rate the intrinsic physical capacity of any wildland fuelbed to release energy, spread, crown, consume, and smolder under extremely dry conditions. They are intended to map fire hazard and to ease communication of the degree of fire hazard. They can also be used in conjunction with knowledge of environmental conditions to approximate fire behavior and effects.

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