International Journal of Wildland Fire International Journal of Wildland Fire Society
Journal of the International Association of Wildland Fire

The importance of fire–atmosphere coupling and boundary-layer turbulence to wildfire spread

Ruiyu Sun A D , Steven K. Krueger A , Mary Ann Jenkins B , Michael A. Zulauf A and Joseph J. Charney C

A Department of Meteorology, University of Utah, Salt Lake City, UT 84112-0110, USA.

B Department of Earth and Space Science and Engineering, Faculty of Pure and Applied Science, York University, Toronto, ON, M3J 1P3, Canada.

C United States Forest Service, North Central Research Station, East Landsing, MI, USA.

D Corresponding author. Email:

International Journal of Wildland Fire 18(1) 50-60
Submitted: 18 May 2007  Accepted: 26 March 2008   Published: 17 February 2009


The major source of uncertainty in wildfire behavior prediction is the transient behavior of wildfire due to changes in flow in the fire’s environment. The changes in flow are dominated by two factors. The first is the interaction or ‘coupling’ between the fire and the fire-induced flow. The second is the interaction or ‘coupling’ between the fire and the ambient flow driven by turbulence due to wind gustiness and eddies in the atmospheric boundary layer (ABL). In the present study, coupled wildfire–atmosphere large-eddy simulations of grassland fires are used to examine the differences in the rate of spread and area burnt by grass fires in two types of ABL, a buoyancy-dominated ABL and a roll-dominated ABL. The simulations show how a buoyancy-dominated ABL affects fire spread, how a roll-dominated ABL affects fire spread, and how fire lines interact with these two different ABL flow types. The simulations also show how important are fire–atmosphere couplings or fire-induced circulations to fire line spread compared with the direct impact of the turbulence in the two different ABLs. The results have implications for operational wildfire behavior prediction. Ultimately, it will be important to use techniques that include an estimate of uncertainty in wildfire behavior forecasts.

Additional keywords: atmospheric boundary layer, coupled atmosphere–wildfire numerical model, fire-induced convection, grassland fire, probabilistic wildfire prediction, rate of fire spread.


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