Wildfire moves faster up a slope
Fire on a slope behaves very differently from fire on flat ground. As flames burn upslope, the heat preheats and dries the fuel above them, so the...
Fire on a slope behaves very differently from fire on flat ground. As flames burn upslope, the heat preheats and dries the fuel above them, so the fire ignites that fuel sooner and spreads faster. As a rule of thumb used by wildfire agencies, fire spreads roughly twice as fast on a slope of about ten degrees compared with flat ground, and faster still on steeper terrain. That matters for homeowners on benches, hillsides and ridge tops across the West, where many properties are perched above forested slopes. The 10-to-30 metre extended zone is even more important on the downslope side of a hillside lot, because that is the side where a fire will arrive first and fastest. Fire-safety agencies recommend a longer fuel-reduced zone on slopes, plus extra attention to the underside of decks, foundation vents and any wood storage on the downhill face. If you are evacuating, leave earlier from a slope home than from a flat lot — your time-to-flame is shorter once a fire is established below you.
A wildfire spreads roughly twice as fast on a 10-degree slope as on flat ground — and faster still on steeper terrain, because flames preheat and dry the fuel above them.
Source: PreparedBC — Wildfires
Last reviewed 2026-05-02.
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