Reconstructing the spread of landscape-scale fires in semi-arid southwestern Australia

Abstract

Landscape-scale fires are a regular feature of semi-arid south-western Australia where the dominant vegetation types are shrubland and eucalypt woodland. Fuel discontinuity limits the spread of fire in some eucalypt woodlands under moderate weather conditions, but fires can spread extensively in woodland under severe fire weather conditions. This paper reconstructs the spread of five large fires ignited by lightning that each burnt more than 90 000 ha. Fires remained active for up to 70 days after ignition until they encountered areas of sparse fuel associated with salt lakes and previous burn scars, or were extinguished by rain. Fire perimeters were mapped using daily NOAA AVHRR and MODIS satellite imagery and used to determine periodic growth in fire area. Weather conditions associated with each fire were examined using observations from a limited number of sites. Fire growth was episodic and strongly associated with periods of high temperature, extreme dryness and strong winds. An event of extraordinary fire growth was identified during the 1994 Forrestania fire which increased in area by more than 350 000 ha during a 24 hour period. The influence of weather on fire spread is being examined using re-analysis data from the European Centre for Medium-Range Weather Forecasting (ECMWF) Interim Re-analysis project ERA-1 which provides spatial and temporal data coverage not otherwise available due to the sparse observation network. South-western Australia provides a unique opportunity to examine factors influencing the duration, scale and growth characteristics of fires burning in semi-arid landscapes unimpeded by fire suppression. High intensity fires can cause widespread mortality of mature woodland trees with recovery to a mature structure taking several centuries, and the role of fire in development and persistence of eucalypt woodlands is currently a topic of scientific interest. This study forms part of a broader examination of the extent of active fire management, including prescribed burning and fire suppression, appropriate in these landscapes.