Bushfires

The effects of fire are complex and governed by components such as frequency, intensity and season. While short-term effects of individual fires are important, it is necessary to evaluate the long-term impacts of fire on social, economic, ecological and natural resource values. Such an evaluation can be used to quantify the risks to particular values.

Research conducted for the Impacts of Climate Change on Natural Hazard Profiles demonstrates that increases in the number and intensity of days of high temperature, low humidity and higher evaporation levels are projected to influence both fire frequency and fire intensity, with the frequency of occurrence of days of very high to extreme fire-risk possibly increasing by 10-50 percent in all State Plan regions of NSW. The fire season is likely to be extended in most regions, but research towards a much better understanding of future changes to the frequency and intensity of El Niño, ignition rates and fuel accumulation is needed to project the extent of the increase. Also, further research is needed to resolve the effects of future changes in moisture and elevated carbon dioxide levels on the frequency and intensity of fires.

Sydney Basin research by OEH and the University of Wollongong

Research was undertaken by OEH and the University of Wollongong that focused on the greater Sydney Basin - a key region where climate change effects regarding bushfires may most acutely affect a wide range of values. Changes to fire in the future are an issue of very high significance in this region because extensive areas of highly fireprone bushland:

1. contain high biodiversity values (e.g. Blue Mountains World Heritage status)
2. abut extensive urban areas
3. directly affect ecosystem services, such as the quantity and quality of water and clean air.

The challenge of resolving and balancing risks posed by bushfires and climate change to these values in the Sydney Basin was the subject of the research project, which aimed to:

• quantify changes in fire regimes resulting from predicted changes in climate
• quantify resultant changes in risks posed to biodiversity, ecosystem functions, and people and their property
• predict ways in which a range of mitigation strategies will deal with risks from bushfires, and the performance of these alternatives under climate change
• investigate trade-offs among risks to key management values that will be needed to adapt to climate change in the Sydney Basin - where high value human assets, ecosystem services, and vulnerable and diverse ecosystems co-exist in fire prone bushland
• report findings through scientific publications, project reports and workshops involving key stakeholder groups in the government and the community.

Research findings

This project is now complete and the report released by the Minister for Climate Change and the Environment in December 2008 (Media release). The report Effects of Climate Change on Bushfire Threats to Biodiversity, Ecosystem Processes and People in the Sydney Region  (or Executive Summary) projects that:

• by 2050, Sydney and the Blue Mountains are likely to experience up to 24 percent more bushfires and that they could cover as much as a 35 percent greater area
• risk to urban catchment areas, and fire sensitive biodiversity could increase by 5-20 percent under the 'high climate change scenario' and < 10 percent under the 'low climate change scenario'
• current levels of prescribed burning (about 1 percent of the landscape treated per annum) resulted in a 5 percent reduction to risk indicators for urban, catchment and biodiversity values
• a five-fold increase in prescribed burning is required to counteract the adverse effects of the 'high climate change scenario', a smaller increase in prescribed burning (two-fold) may be needed to mitigate effects of the 'low climate change scenario'.

The report's authors stress that other factors affecting the built environment will govern overall levels of risk to people and property, and that the results of this report summarise the contribution to urban risk posed by the condition of the landscape only.

The authors also stress that changes to ignition rates from lightning, the amount of fuel and the effects of elevated CO₂ on plant growth that may result from climatechange were not addressed in detail. However, a preliminary sensitivity analysis indicated that a 10 percent decline in fuel accumulation may reduce the area burnt by 20 percent and that such an effect would cancel out the increase predicted under the 'high climate change scenario'.

For more information

Climate Change and Bushfire Risk- Prof Ross Bradstock (PDF 786kb). Presentation of research at the NSW Climate Impacts and Adaptation Summit, 23 February 2007. The report contains sections entitled 'When do bushfires fires threaten people and property?' 'How will' 'fire weather' 'change?' 'How will bushfire fire incidence/the area burned change?' 'Changes in risks to people & property?' and 'Future management and other consequences?'