- Title:
-
Existing Fire Behaviour Models Under-predict the Rate of Spread of Summer Fires in Open Jarrah (Eucalyptus Marginata) Forest
- Date:
- March 2008
- Organisations
- Australian Forestry Journal
- Authors:
- McCaw, W. L., Gould, J. S., Cheney, N. P.
-
Location:
-
Australia,
Australia
Overview
Fire behaviour data from Project Vesta
experimental fires were used to evaluate the fire behaviour relationship on the Forest Fire Danger Meter (FFDM), the Forest Fire Behaviour
Tables (FFBT) for Western Australia and the fire spread model of Burrows (1999) for predicting the rate of spread of fires in jarrah (Eucalyptus marginata) forest under dry summer conditions. Experimental fires were conducted at two sites in southwestern Australia under conditions of
moderate to high forest fire danger with fine fuel moisture contents of
6-9% oven dry weight and wind speeds up to 20 km h-1 (at 10 m in the
open). Fuels ranged in age from 2 to 22 y since the last fire and had
understorey shrub layers from 0.5 to 2.0 m tall. Mean rates of spread
for experimental fires were 392 m h-1 and 405 m h-1 at the low and tall
shrub sites respectively, with the fastest fires spreading at close to
1200 m h-1. Fires spread two to three times faster than predicted by the FFDM and FFBT fire spread models, and up to five times faster than
predicted by the spread model of Burrows. Both the FFDM and FFBT models
predicted fire spread better at the low shrub fuel site and when wind
speeds were <12.5 km h-1. All models under-predicted fire spread at
the tall shrub site and grossly under-predicted fire spread when wind
speeds were >12.5 km h-1. We argue that existing fire behaviour
models under-predict because they were developed using data from fires
that had not achieved a quasi-steady rate of spread, whereas the line
ignition technique used during Project Vesta experiments resulted in
fires travelling at a speed closer to their potential rate of spread for the prevailing conditions. Existing guides remain valid for predicting
spread during the early stages of fire growth when fires are developing
from a point ignition and the headfire remains narrow.
