Use of the Extreme Value Analysis in Determining Annual Probability of Exceedance for Bushfire Protection Design

Historically extreme value analysis has been used to guide human activities against many forms of natural hazards such as floods, storms, heat waves and wind. However, it has not been used for extreme fire weather assessment. This may be because forest fire danger index is a composite of differing parameters which may not be regarded as being associated with adverse fire weather individually, however, collectively may result in Extreme fire weather conditions. This paper offers new insights in the use of the extreme value analysis for the McArthur Forest Fire Danger Index (FFDI) so as to provide a scientific basis for planning, development and building construction in bushfire prone areas. The underlying principle is to use the recurrence of fire weather as measured by FFDI as the planning or design fire weather reference. The recurrence is determined by the applying the Generalised Extreme Value Analysis to local historical weather data of limited time period. The resultant distribution is fitted with an appropriate regression curve which allows the extrapolation beyond the available weather data recording period. The method is applied to a number of weather districts in the state of New South Wales of Australia. The derived FFDIs corresponding to the nominated recurrence is compared with the FFDIs based on traditional empirical methods.