Coupled Fire/Atmosphere Modeling, FIRETEC

Understanding and predicting wildfire behavior is a particularly difficult scientific problem, since the length scales of the physics range from those of flame sheets to fire and topography influenced atmospheric dynamics.  Wildfires are driven by very complex processes ranging from combustion of complex natural fuels to local meteorology and their behavior depends heavily on the coupling between a variety of chemical and physical processes.  An atmospheric hydrodynamics model, HIGRAD, is coupled to a wildfire behavior model, FIRETEC, to produce a coupled atmosphere/wildfire behavior model based on conservation of mass, momentum, species, and energy.  HIGRAD/FIRETEC is a three-dimensional transport model that uses a compressible-gas formulation to simulation the coupling between wildland fire and motions of the local atmosphere.  HIGRAD/FIRETEC is an attempt to capture the combined essence of the driving physical processes that control a wildland fires over landscape scales (100s to 1000s of meters.)  This objective precludes the use of existing simplified empirical wildfire models because they do not predict general fire behavior and high-resolution, high-fidelity combustion are not currently appropriate because of their computational expense.  Therefore FIRETEC employs a multiphase approach together with ensemble averages and probability distribution functions to capture the combined effects of the unresolved details of the fuel bed and many fine-scale processes. Currently, HIGRAD/FIRETEC is being used to study the interaction between nonhomogeneities in vegetation, topography, and atmospheric conditions.  Examples of the types of physical phenomenon of interest are the effects of transient wind conditions (i.e. gusts and meteorological changes), the effects of nonhomogeneous terrain (i.e. upslope canyons,  saddles), and the effects of nonuniform fuels (i.e. patchy distributions), and influence of other disturbances on fire behavior (i.e. bark beetle attacks and fuels management tactics.)

This work is a collaborative effort with USDA Forest Service, Rocky Mountain Research Station (under the direction of Carolyn Sieg), and Institut National pour la Recherche Agronomique (INRA) of France.

Left Image: HIGRAD/FIRETEC simulation of fire burning upslope into a saddle.  This movie illustrates the coupled fire/atmosphere behavior including influences of a saddle-type topographic setting. Click HERE or on the image for the movie.

Right Image: HIGRAD/FIRETEC simulation of fire behavior in a lodgepole pine forest after a bark beetle attack has created a heterogeneous canopy and dead litter layer. Click HERE to download the movie.