The fluid dynamics of steady-state fireline propagation

One aspect of wildland fire behavior that requires deeper understanding in order to further aid fire control and fire fighter safety is the propagation of the fireline.

Can the propagation of a wildfire be accurately predicted based on the strength and direction of the mean upstream near-surface wind? We suggest that the correct response is no. Accurate prediction of wildfire behavior and propagation is only possible when the coupling between the entire fire, including its plume, and atmosphere is accounted for. We will attempt to explain fireline propagation as the result of dynamical interactions between pressure perturbations, vorticity development, and wind patterns. WRF-Fire simulations of propagating grassfires in environments with a uni-directional wind profile (with or without vertical shear) are used to demonstrate how these flow dynamics are responsible for fireline propagation.

WRF-Fire combines the Weather Research and Forecasting model (WRF) with a fire code implementing a semi-empirical surface fire behavior model that calculates the rate of spread of the fire line based on fuel properties, wind velocities from WRF, and terrain slope.