Russ Parsons1, Jeremy Sauer2, Rodd Linn3  1USDA Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory 2Florida State University, Tallahassee Florida. 3 Los Alamos National Laboratory, Los Alamos, New Mexico Abstract Wildland fuels are highly variable in space, with significant differences in fundamental fuels properties, such as bulk density (fuel load quantity / specified volume, kg/m3) occurring over spatial scales of a few meters. Operational fire behavior prediction models do not consider spatial variability in fuels at this scale, assuming that fine scale variability will average out over larger space and time scales. However, this assumption has not been subjected to rigorous testing. In this project we use a physics based numerical fire behavior model, FIRETEC, to assess the impact of spatial variability in tree crowns on surface fire behavior. We establish a simulated forest consisting of 2000 simulated tree crowns randomly located within a spatial domain measuring 320 m x 160 m (about 12.7 acres). Holding total initial quantities of crown fuel constant for all simulations, we randomly rearrange the horizontal and vertical positions of tree crowns within the central portion of the domain to create a series of scenarios representing different levels of horizontal clumping and vertical variability. We then simulate fire behavior for each scenario using the FIRETEC model. We compare each simulation in terms of the horizontal spread rate achieved over the same time period. Our preliminary results demonstrate that significant differences in fire behavior resulted from variability alone, even though the total and average fuel quantities remained constant. The primary mechanism responsible appears to be modification of the wind fields by the altered patterns of fuel bulk density. Our findings have implications for our ability to predict the change in fire behavior arising from fuel treatments, and offer insights relevant to an improved understanding of fire and fuels interactions. Objectives: - Test variables in fuels bulk density occurring in vertical and horizontal distribution.
- Determine if spatial variations on the scale of several meters affect fire behavior, rate of spread, and consumption.
Status Research paper expected to be complete by December 2007. Products - Research paper currently in development.
- Simulations-
- An animation illustrating the capacity of the FIRETEC model to address the complex dynamics of wildland fire behavior. The movie shows two fire simulations. In the top simulation trees are randomly located. In the bottom simulation, trees within the central portion of the spatial domain have been moved horizontally into a series of clumps. The total quantity of fuels remains the same in both simulations but the clumped simulation has higher density within clumps. (AVI file)
- Figure showing a planimetric view of the two simulations after four minutes of simulated fire spread. The clumped scenario (bottom) had a forward spread rate about 40% less than the random fuel configuration (top).
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