Predicting fire behaviour in dry eucalypt forest in southern Australia

Abstract

This paper describes the development of two empirical models to predict the potential spread of an established line of fire in dry eucalypt forest with a shrubby understorey. These models use inputs of fine fuel moisture, wind speed, near-surface fuel height, and either a numerical fuel hazard score or a descriptive fuel rating for the surface and near-surface fuel. A model to predict flame height from rate of spread and elevated fuel height is also presented as a guide to suppression difficulty.Models were developed using data from a series of simultaneous experimental fires in fuels of different fuel ages ranging from 2 to 22years since last fire. They were tested against data from independent experimental fires and well documented wildfires that were assigned reliability ratings for fuel, weather and spread rate. Models performed reliably when the reliability of wildfire data ratings for fuel and weather were also high.Models predict the potential rate of spread and are likely to over-predict the spread of fires starting from a point ignition during the early stages of development when the headfire is less than 120m wide. Existing guides should be used for prescribed burning operations based on point ignition, and the models described here can be used to predict rate of spread from line ignition.Predictions from the new models will be more reliable when rate of spread is averaged over an interval of 30min or longer. The reliability will be low when compared to observations made over short time intervals, at specific points in the topography, or when very large fires interact to produce wind speeds that are very different to the ambient wind in the open.