The fire forecast system FWI, which is used primarily in Canada and UK has its base on two intermediate Fire Behavior Indices values: The buildup index (BUI) and the Initial Spread Index (ISI). The ISI indices provide estimated value of the combined impact of wind speed and the FFMC on the projected spread of forest fire. The developed equation is a simple exponential function which provides double the value of FWI for the wind speed increment of about 20 Km per hour. The second indices, the buildup index are a combined form of DMC and the Drought Code (DC), and it refers to the availability of deeper or large amounts of fuel for the forest fire. The FWI value is calculated by the combination of the ISI and BUI values, and it represents the highest daily intensity by which the fire can spread, in terms of the energy output rate for the per unit length of the fire.
THE RELATIONSHIP BETWEEN THE FFDI AND FWI
Here, the FFDI system and the FWI systems are compared with each other. Various similarities between the two systems and the differences between these two systems are analyzed in this part of the paper. As a result of the comparison, a relationship would be identified between these two types of forest fire indices systems. The relationship amongst the FWI and FFDI systems is developed in order to generate an indication of the fire danger threshold value of the FWI system for its implementation in the Australian forests (basing the implementation of the FFDI thresholds which were shown in the table 1)(Berry, 1974). Once the relationship has been established, scatter plots are used to further investigate the accuracy of the relationship identified between the two indices, by an analysis of the days when the two indices provide large difference between their values.