What is the relationship between slope and fire spread?

The relationship between slope and fire spread is fundamentally grounded in the principles of fire behavior. A steeper slope usually accelerates fire spread due to the way flames interact with the fuels located on the incline. When a fire is on a slope, the heat from the flames rises, creating convection currents that preheat the fuel above. This effect is enhanced on steeper slopes because the flames can extend further upward, promoting faster ignition of the fuel ahead of the fire.

Additionally, as the fire moves up a slope, the overall energy and intensity of the fire increase. The fire rises more quickly because it is climbing toward previously unburned fuels, and the combination of increased heat and the alignment of fuels with the slope creates an effect that intensifies the rate of spread.

Conversely, moderate or gentle slopes do not generally have the same effect. A moderate slope may not significantly influence the fire's behavior because it doesn't promote the same strong convection currents, while a gentle slope is unlikely to significantly affect the fire spread at all. Therefore, the understanding of how slope influences fire dynamics is critical for predicting fire behavior and for developing appropriate firefighting strategies.