During the period 1973-2009, the area burned in southeast Australia has increased in seven out of eight forest biomes (Bradstock et al. 2014).
Since the start of the 21st century, large and uncontrollable fires destroyed 500 houses in Canberra in 2003, bush fires in Victoria in 2009 claimed 173 lives and destroyed over 2,000 houses, and in 2013 large fires in Tasmania destroyed nearly 200 properties and forced the evacuation of hundreds of people from the Tasman Peninsula.
The West Australia town of Yarloop, located on the coast south of Perth, experienced
one of Australia’s worst bush fires in 2016.
With minimal warning, the fires reached Yarloop and destroyed the entire town centre (ABC 2016a).
121 homes were destroyed and approximately 67,000 hectares of land were burned (ABC 2016a).
The fire was so intense that it created its own weather system, causing rainfall and triggering extensive lightning.
The bush fire occurred during a strong El Niño event, bringing warmer and drier weather to western Australia (BoM 2016d), in addition to the long-term trend of a warming climate.
The impacts of a changing climate on bushfire regimes are complex.
A fire needs to be started (ignition), it needs something to burn (fuel), and it needs conditions that are conducive to its spread (weather) (Bradstock et al. 2014)
While a fire must be ignited (by humans or lightning), the main determinants of whether a fire will take hold are the condition of the fuel and the weather, which are linked.
The influence of climate change on the amount and condition of
the fuel is complex.
For example, increases
in rainfall may dampen the bushfire risk
in one year by keeping the fuel load wetter, but increase the risk in subsequent years
by enhancing vegetation growth and thus increasing the fuel load in the longer term.
It is clear, however, that climate change is driving up the likelihood of dangerous re weather.
At higher temperatures, fuel is ‘desiccated’ and is more likely to ignite and to continue to burn (Geoscience Australia 2015).
In addition, fires are more likely to break out on days that are very hot, with low humidity and high winds – that, is high fire danger weather (Clarke et al. 2013).
Heatwaves are becoming hotter, longer and more frequent, which is contributing to an increase in dangerous bushfire weather.
Also, over the past several decades in the southeast and southwest of Australia, there has been a drying trend characterised by declining rainfall and soil moisture (CSIRO and BoM 2014).
Contributing to this drying trend is a southward shift of fronts that bring rain to southern Australia in the cooler months of the year (CSIRO and BoM 2015).
In very dry conditions, with relative humidity less than around 20%, fuel dries out and becomes more ammable (BoM 2009). Jolly et al. (2015) and Williamson et al. (2016) highlighted that the combination of droughts and heatwaves contribute significantly to particularly bad fire seasons in Australia’s southeast.
A study into forested regions of Australia found that, in the majority of cases, years with drought conditions resulted in a greater area of burned land (Bradstock et al. 2014).
Press link for full report: Climate Council