Physical Modelling of Leaf Scorch Height From Prescribed Fires in Young Eucalyptus Sieberi Regrowth Forests in South-Eastern Australia

Abstract

Information on weather, fuel and fire behaviour were recorded on 56 experimental prescribed fires in young coastal silvertop ash (Eucalyptus sieberi) regrowth forest in south-east New South Wales, Australia. The thermal environment above the fire was measured in 14 of those fires. Existing plume models, based on the assumption of a uniformly burning line fire, were found to under-predict the temperature of the air rising into the canopy. An axially symmetric plume model, based on the observation that fires burning in non-uniform fuels are not uniformly burning line fires, was developed using standard plume rise equations. This model, called the Sporadic Axial Model (SAM), was calibrated using data from one fire. This model can be used to predict scorch height from known ambient temperature and Byram's fire line intensity. The SAM model suggests that scorch height will be greater for prescribed fires burnt under calm conditions than prescribed fires of the same intensity burnt under stronger wind conditions.