APP – Topography and Slope effect on Fire Behaviour

Effects of Slope on Fire Behavior Calculator




1. Important information:

The fastest bushfire ever recorded in Australia, and indeed one of the fastest in the world, was the 2003 Canberra bushfires. These fires exhibited extreme behavior, with fire fronts moving at speeds of up to 12.6 kilometers per hour (7.8 miles per hour).

The fastest grass fire ever recorded in Australia was during the Black Saturday bushfires on February 7, 2009. During this catastrophic event, the fire front moved at an exceptional speed, estimated to be over 120 kilometers per hour (75 miles per hour) in some instances.


2. A explanation of the “Slope effect on fire” calcuator

  • For every 10 degrees of slope increase, the fire’s rate of spread is expected to double.


Slope Gradient (%) Slope Angle (Degrees) Relative Rate of Spread
0 0 1x
20 11 2x
45 24 4x
70 35 8x
100 45 16x



Initial Fire Speed (km/h) Slope Degree (Degrees) Resulting Fire Speed (km/h)
5 0 5
5 10 (uphill) 10
5 20 (uphill) 20
5 -10 (downhill) 2.5
5 -20 (downhill) 1.25


  • Note: This table is a simplification and actual fire behavior can be influenced by various other factors including fuel type, moisture content, and weather conditions.

3. In summary

understanding the impact of slope on fire behavior is critical for predicting and managing wildfires. The role of slope must be considered along with other environmental and weather factors to accurately assess and respond to wildfire risks.

4. Watch on YouTube:

The effects of slope on fire behavior are a crucial aspect of wildfire management and understanding. The primary mechanism through which slope impacts fire behavior is through the preheating of fuels uphill from the fire. As a fire burns, it radiates heat upwards, which preheats the fuel above it on a slope. This makes the fuel more combustible, and as a result, fires tend to move faster uphill.

5. Here are some key points regarding the effects of slope on fire behavior:

  1. Rate of Spread: Fires on steeper slopes spread more rapidly. This is due to the fact that flames are closer to the unburnt fuel above them on steep slopes, causing more efficient preheating and drying of the fuel.
  2. Flame Length: Flame length can be significantly longer on slopes, especially on steep terrain, as the flames reach upwards towards the fuel.
  3. Direction and Intensity: The direction of the slope can influence the fire’s direction, with fires generally moving uphill. The intensity of the fire also increases with the steepness of the slope.
  4. Wind Effects: Slopes can also influence local wind patterns, which can further exacerbate fire behavior. Upslope winds can drive fires uphill more quickly.
  5. Fuel Arrangement: The arrangement of fuel on slopes can also affect fire behavior. For example, vertical arrangement of fuel (like trees) can facilitate faster spread of fire uphill.