The Australian FFDI Compresses Drought, Heat, Humidity and Wind into One Number
McArthur's Forest Fire Danger Index reduces fire danger to a single value computed from a drought factor, air temperature, relative humidity and wind speed, with a companion Grassland Fire Danger Index that substitutes curing and fuel load for the forest terms. It is an open-ended scale calibrated so that \( 100 \) corresponds to the conditions of the 1939 Black Friday fires; the catastrophic category added after 2009 begins at \( 100 \), and values above \( 150 \) have been recorded. Australia moved its operational public ratings to the Australian Fire Danger Rating System in 2022, which computes a Fire Behaviour Index from fuel-type-specific models, but FFDI remains the reference in the research literature and in the historical record. The confusion this resolves is comparing danger numbers across countries: an FFDI of \( 50 \) and a Canadian FWI of \( 50 \) share a digit and nothing else. After this Concept you can read an Australian fire danger figure and place it against the event its scale was calibrated to.
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McArthur's Forest Fire Danger Index reduces fire danger to a single value computed from a drought factor, air temperature, relative humidity and wind speed, with a companion Grassland Fire Danger Index that substitutes curing and fuel load for the forest terms. It is an open-ended scale calibrated so that \( 100 \) corresponds to the conditions of the 1939 Black Friday fires; the catastrophic category added after 2009 begins at \( 100 \), and values above \( 150 \) have been recorded. Australia moved its operational public ratings to the Australian Fire Danger Rating System in 2022, which computes a Fire Behaviour Index from fuel-type-specific models, but FFDI remains the reference in the research literature and in the historical record. The confusion this resolves is comparing danger numbers across countries: an FFDI of \( 50 \) and a Canadian FWI of \( 50 \) share a digit and nothing else. After this Concept you can read an Australian fire danger figure and place it against the event its scale was calibrated to.
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