Terrian Difficulty Index

Reflects the difficulty to suppress a fire given the terrain and vegetation conditions that may impact ground resource access and capabilities.

The Terrain Difficulty Index (TDI) is a metric that describes the characteristics of the landscape which evaluates the difficulty of extinction, especially in initial attack, although it can also be extrapolated to extended attacks. This static index quantifies the availability of access for the arrival of terrestrial means, the ability to penetrate the area where the fire originates, and the difficulty of extinguishing fuels.

Indicators such as the Accessibility Index, Penetrability Index and Fireline Opening Index (construction) have been used for the formulation of TDI. This index is based on other indices such as the Wildfire Suppression Difficulty Index (terrestrial) (SDIt) (Matthew P Thompson et al, 2018. Francisco Rodriguez and Silva et al, 2020.) which is a quantitative rating of the relative difficulty to perform fire control work. However, TDI is dynamic as it incorporates changes in surface fuels over time providing a less static perspective for a planning point of view.

Class 1, Very low: No accessibility limitations to the firefighting resources, allowing quick
deployment of wildfire suppression ground resources.
Class 2, Low: High density of tracks and paths. Terrain conditions allow the deployment of
wildfire suppression ground resources.
Class 3, Intermediate: Roads and tracks are slightly more difficult to access and terrain is mildly
difficult with increasing slopes.
Class 4, High: Low density of roads/tracks in the area. Difficult terrain access with limitations to
ground travel.
Class 5, Extreme: Very low density of tracks/roads to support strategies. Highly complex terrain
conditions including high-slope areas limit the use of heavy equipment.