Model Pinpoints Factors Driving Extreme Bushfire Behaviour

Fire Note 137: In the 2003 Canberra bushfires, a number of unusual fires were observed in which bushfire spread sideways in a diagonal or crosswise direction to background winds. It occurred alongside rapid and intense downwind fire spread due to spotting. The atypical fire occurrence was on steep leeward slopes (a sheltered slope facing away from the wind) where background wind was mostly perpendicular to the terrain.

The WRF-Fire coupled atmosphere-fire model was used extensively to examine both the physical mechanism driving the atypical lateral fire spread, as well as its sensitivity to the fire environment conditions. The numerical simulations qualitatively match the fire spread seen in the 2003 Canberra bushfires, and provide new insights into dynamic modes of fire spread in rugged terrain. The results have important implications for firefighter safety and fire management.