A numerical study of slope and fuel structure effects on coupled wildfire behaviour

Slope and fuel structure are commonly accepted as major factors affecting the way wildfires behave. However, it is possible that slope affects fire differently depending on the fuel bed. Six FIRETEC simulations using three different fuel beds on flat and upslope topography were used to examine this possibility. Fuel beds resembling grass, chaparral, and ponderosa pine forests were created in such a way that there were two specific locations with identical local fuel beds located around them. These fuel beds were each used for a flat-terrain simulation and an idealised-hill simulation in order to isolate the impacts of the topography without the complications of having different local fuels. In these simulations, fuel bed characteristics have a significant effect on the spread rate and perimeter shape of the fires on both flat ground and on the idealised smooth hill topography. The analysis showed that these simulated fires evolved as they travelled between the locations even on flat ground, and the accelerations and decelerations that affect the fire occurred at different times and at different rates depending on the fuel bed. The results of these simulations and analyses indicate that though some general principles are true for all fuel beds, there are differences in the way that fires react to non-homogeneous topographies depending on the fuel bed.