Wildfire Severity Mapping—Canberra

In January 2003, fires spread throughout the eastern states of Australia causing evacuations, loss of livestock, and loss of property. In the Australian Capital Territory (ACT), fires were particularly devastating because of the rate of spread and the area they covered. On January 8, electrical storms ignited five fires in the Brindabella range to the east of Canberra. All five fires remained small, burning approximately 70 square kilometers (27 square miles) in the eight days following their ignition. On January 18, fires fanned by winds reaching speeds of 100 kilometers per hour, and hot, dry conditions burned 1,649 square kilometers. Some 80 percent of ACT were fire affected.

The wildfires resulted in the loss of four lives, 500 homes, and 50,000 electricity and 7,000 gas customers temporarily lost their services. In addition, 100 percent (200 square kilometers) of the primary water catchment (Cotter Catchment) was burned. Key water treatment processes were inoperable for nine hours, and sewage treatment processes were inoperable for two and one-half days.

In the years prior to the 2003 fires, the Cotter Catchment supplied up to 95 percent of water for more than 350,000 Canberra residents. The catchment formed an essential barrier to water pollutants, both naturally occurring and anthropogenic, and the ecosystem services it provided made the ACT water supply one of the most pure in Australia, requiring only lime pH adjustment, chlorination, and fluoridation.

In many of the most hydrologically significant areas, the catchment had been completely denuded of vegetation, both the understory and the canopy. The loss of vegetation and swamps during the fires has dramatically changed the water quality at the reservoir. Turbidity, iron, and manganese are now water quality issues. In response to the degradation of water quality, a new treatment plant will be constructed. In keeping with the multibarrier approach to maintaining water quality, time and resources have been focused on the catchment to assist with rehabilitation and future management.

The inaccessible nature of the catchment meant that remote sensing was an ideal tool for initial rapid assessment. The methodologies employed in the fire severity mapping were developed toward an industry standard with other authorities and organizations. The purpose of this analysis was to provide catchment managers with a method of prioritizing catchment activities to manage the effects of fires on water quality and hydrology. Prefire and postfire Landsat Thematic Mapper images were analyzed to create a data set showing the severity of the burn in the catchment.

Remote sensing analysis will be repeated in 2004 to monitor vegetation recovery.