The importance of low-level environmental vertical wind shear to wildfire propagation: Proof of concept

Abstract

This study is a proof of concept of the sensitivity of grassfire propagation to vertical shear in the near-surface environmental flow found through four comparative grassfire numerical simulations with a coupled wildfire-atmosphere model. A unidirectional constant wind field, under neutral atmospheric conditions, no surface friction, Coriolis force or topography, and homogeneous fuel, prescribes the model environment. By using the same surface (at 6.2 m above ground level) wind speed for all simulations, analyses of the results can suggest when the behavior and spread rate of the fire may depend more on the interaction of the fire plume with the shear in the above surface wind or more on the magnitude of the mean upstream surface wind speed at the surface. Three aspects of wildfire behavior are investigated: impact of unidirectional vertical shear on surface flow properties and fire line propagation; variability in fire spread and area burnt due to the evolution of the surface flow; and implications of low-level vertical wind shear on the prediction of wildfire, especially extreme or erratic, behavior. Key Points Above-surface wind affects wildfire propagation, behavior, prediction Vertical-wind-shear/fire-interaction can be cause of erratic wildfire behavior A probability forecast for fire behavior is necessary ©2013. American Geophysical Union. All Rights Reserved.