The index combines a record of dryness, based on rainfall and evaporation, with meteorological variables for wind speed, temperature and humidity.
The power function nature of the algorithm, together with limits of precision in measuring the input variables, may result in a large range of uncertainty in the calculated FFDI.
For grassland fuels the threshold FDI values for the Extreme and Catastrophic ratings were increased to 100 and 150 respectively.
After the Black Saturday bushfires, the McArthur Forest Fire Danger Index was revised.
The category "Catastrophic" was added to help identify those situations where fires will spread so quickly that they present a critical threat to life and safety.