Critical roles of three-dimensional atmosphere/fire coupling on wildfire behavior

It has long been accepted that atmospheric processes play important roles in wildfire behavior. A widely observed example is the effect that wind speed has on fire spread rate in the same direction. In fact, simplified wildfire behavior models often represent fire spread rates in a given direction as functions of the magnitude of the wind component in that direction. These models seldom account for nonlocal fire shape or the turbulent mixing of the wind fields around fires due to the complexity that these issues add. Unfortunately, there are important nonlinear interactions between fires and surrounding winds and these interactions result in flow-fields that are three-dimensional in nature or nonhomogeneous in all directions. This three-dimensionality has influences on many aspects of fire behavior and it greatly complicates development theoretical or computational models for fire spread using either one-dimensional or two-dimensional approaches. Empirically-based models often intrinsically account for these influences in situations where applications are similar to experiments, but in other situations these influences can make it very difficult to extrapolate to more complex settings. A physics-based coupled atmosphere/fire behavior model, HIGRAD FIRETEC is used to isolate and study the impacts of three-dimensional aspects of the atmosphere/fire coupling. These three-dimensional atmosphere/fire interactions would be further complicated in reality by nonhomgeneous fuels, winds, and topography, but in this study idealized scenarios are simulated in order to identify the importance of both local and non local three-dimensional effects. Results from this exploration provide insight into essential concepts that must be accounted for when developing simplified models.