Influence of wind variations and fluctuations on fire behavior in FIRETEC simulations

Wildfire behavior is influenced by a variety of factors including characteristics of the vegetation, topography, and atmosphere. An environmental factor that fires are especially sensitive to is the ambient wind. The forces provided by the ambient winds combine with the buoyancy from the fire to produce a complex set of winds in the vicinity of the fire. These winds contribute to establishing the sometimes delicate balances between convective and radiative heat transfer to unburned fuel, which can result in fire spread in marginal conditions as well as cause dramatic increases in fire behavior in other situations. The winds that blow towards a fire often include spatial fluctuations and temporal variations, which come in a variety of spatial scales (sub-meter up to landscape scale), time scales (sub-second to tens of minutes), and magnitudes. In some cases the magnitude of the fluctuations in the wind (or gusts) may be significantly larger than the mean wind. FIRETEC is a three-dimensional physic-based wildfire behavior model that has been used to simulate fires in a variety of conditions. In FIRETEC simulations, the nature of the wind fluctuations can play a significant role in the simulated fire behavior. In FIRETEC simulations variations in the wind field are sometimes created by shear induced turbulence, nonsteady fire behavior, topography, or inhomogeneous vegetation even if initial and boundary conditions are prescribed without any fluctuations. In other cases, fluctuations in the wind field are prescribed in the initial and boundary conditions with a single scale or with a spectrum of scales. The influences of these fluctuations are very significant in many cases and might provide insight into some facets of fire behavior that are not as well understood as wind-driven head fires.