How does the rate of spread change with slope?

The correct choice indicates that the rate of spread of a fire increases significantly with the slope of the terrain. Specifically, it states that for each 20% increase in slope, the rate of spread doubles. This is due to the fact that fire moves more rapidly uphill as the flames and heat rise towards the unburned fuel above. The steeper the slope, the more pronounced this effect becomes, as the fire is able to access more fuel and generate more heat, which accelerates the combustion process.

Understanding this relationship is crucial for firefighting strategies and tactics, as it helps captains and crews to anticipate the behavior of a fire in hilly or mountainous areas. It allows them to plan actions effectively, whether it involves constructing fire lines, deploying resources, or predicting potential areas of risk.

In contrast, factors such as constant rates regardless of slope, decreases in spread, or fluctuations based on weather do not accurately represent the dynamics of fire behavior in sloped terrains. Such assumptions could lead to ineffective firefighting measures and increased risks for both personnel and the surrounding environment.