Developing an impact index for the Australian Fire Danger Rating System: predicting potential structure loss from wildfires

Background: Accurately predicting impacts of wildfires remains a top priority for fire and land management agencies. The Australian Fire Danger Rating System (AFDRS) redesigned forecasts of fire danger for Australian fire agencies, modernising the fire danger system. The next phase of the AFDRS focuses on developing indices for Fire Ignition, Suppression and Impact (FISI). Aims: Impact models were developed to predict structure loss at the bushland–urban interface in eastern Australia. Methods: Structure counts, cleared land and canopy height, calculated at radii 50–1000 m from structures, as well as terrain ruggedness, were used to model individual structure loss during wildfire and proportional loss in built-up areas. Key results: The individual and proportional structure loss models accurately predicted structure loss (individual losses: true positive rate (TPR) = 0.67, true negative rate (TNR) = 0.69; proportional loss r²  = 0.71). Loss was lowest where structures had defensible space on flat ground, with higher numbers of structures nearby and shorter vegetation canopy height. Conclusions: The models determine the probability of structure loss during destructive wildfire. Implications: These models provide fire agencies information on the likelihood of structure loss and aid in decision-making. The impact index may support effective resource allocation, potentially reducing structure loss.