Operational Systems Like the Canadian FBP Predict Spread from Fitted Curves
Not every operational spread model is built from an energy balance. The Canadian Fire Behaviour Prediction system takes a different route: for each of sixteen named fuel types, it supplies an equation of the form \( ROS = a \left( 1 - e^{-b \cdot ISI} \right)^{c} \), whose coefficients were fitted to hundreds of documented experimental and wildfire observations in that fuel type, with the Initial Spread Index carrying wind and fine fuel moisture. Australia's McArthur meters do the same thing in an even more compact form, originally as a cardboard slide rule. These systems are honest empirical models: they are accurate in the fuels and conditions they were fitted to, they require no laboratory closure constants, and they say nothing defensible about a fuel type not in the list. The confusion this resolves is that a fitted operational system is not a cruder version of Rothermel; it is a different bargain, buying local accuracy with loss of transferability. After this Concept you can explain why a fitted spread system may beat a physical one locally and fail entirely elsewhere.
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Not every operational spread model is built from an energy balance. The Canadian Fire Behaviour Prediction system takes a different route: for each of sixteen named fuel types, it supplies an equation of the form \( ROS = a \left( 1 - e^{-b \cdot ISI} \right)^{c} \), whose coefficients were fitted to hundreds of documented experimental and wildfire observations in that fuel type, with the Initial Spread Index carrying wind and fine fuel moisture. Australia's McArthur meters do the same thing in an even more compact form, originally as a cardboard slide rule. These systems are honest empirical models: they are accurate in the fuels and conditions they were fitted to, they require no laboratory closure constants, and they say nothing defensible about a fuel type not in the list. The confusion this resolves is that a fitted operational system is not a cruder version of Rothermel; it is a different bargain, buying local accuracy with loss of transferability. After this Concept you can explain why a fitted spread system may beat a physical one locally and fail entirely elsewhere.
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