Bushfires in Southeast Australia

Over the Christmas break this year, I hopped onto the plane and headed down under, towards Australia! During the trip, I visited the Blue Mountains, just west of Sydney, some parts of which were recently ravaged by major bushfires in October. While bushfires may not be as widely researched and discussed as the other types of natural disasters that I have brought up in the previous posts, it has nonetheless been a recurring phenomenon in Australia for millions of years. As such, I will briefly touch on the impacts of climate change on bushfires in Australia, particular the southeastern region, in this post.

Bushfires on Blue Mountain in October 2013. Credits: AFP

Southeastern Australia is one the top 3 fire prone regions in the world, together with southern California and southern France. In the past century, bushfires have destroyed thousands of homes and claimed hundreds of lives including the infamous Black Friday fires in 1939 and Ash Wednesday fires in 1983. One of the driving factors that have caused southeastern Australia to be particularly vulnerable to bushfires is its climate – hot, dry summers and mild, wet winters. The precipitation received during winter and spring allows fuel (the vegetation) to grow, while the dry summers favour the development of bushfires (Lucas et al. 2007). Moreover, periods of drought have exacerbated the dry conditions and fire risks in the region. Over the past decade, it has been observed that temperatures of the region have shifted towards higher temperatures, while rainfall has declined below the 1961-1990 mean (Murphy and Timbal 2008). The extended period of dry conditions have contributed to the large fires that burned with little control in 2006/07.  

Eucaplyptus trees that are commonly found in Australia. Credits: Joon Ting

Another factor that has been blamed for the bushfires is the predominant type of vegetation that lines the landscape of Australia – eucalypts. There are more than 800 endemic species found in Australia and forms the main diet for koalas. These trees are highly flammable as they contain oil, which gives them their distinct spicy fragrance. During periods of dry and windy conditions, their flammable oil can cause small fires to develop into huge firestorms very rapidly. Yet, these trees are extremely fire resistant themselves and tend to survive the bushfires, allowing for the regeneration of the eucalyptus forest after the fire. Hence, they tend to be naturally selected in regions prone to bushfires including Australia and California, where they continue to dominate the landscape. As such, it seems inevitable that southeast Australia experiences such frequent bushfires.

Eucaplytus trees that cover the Blue Mountains. Credits: Joon Ting

It has already been projected that southeast Australia will become hotter and drier under climate change (Suppiah et al. 2004). Modelling studies have been further carried out to determine how this projected change in climate will affect the fire risks of the region. The Forest Fire Danger Index (FFDI) has been used to quantify the fire risks and is calculated based on observations of temperature, relative humidity and wind speed. Modelling studies carried out by Hennessy et al. (2005) on 17 sites in southeast Australia have suggested that the combined frequencies of days with very high and extreme FFDI rating are likely to increase by 4-25% by 2020 and 15-70% by 2050. This corresponds with more recent studies by Lucas et al. (2007) that show that the increase in annual cumulative FFDI is generally 0-4% in the low scenarios and 0-10% in the high scenarios by 2020, and 0-8% in the low scenarios and 10-30% in the high scenarios by 2050.

Nonetheless, there is still large uncertainty in these studies given that much of the climate of southeast Australia is dominated by interannual and interdecadal variability that is influenced by complex systems including ENSO and Southern Hemisphere Annular Mode (SAM). The evolution of these systems under future climate change is still not fully understood thus it is difficult to ascertain how fire weather and risks will change in future when such variability is taken into account (Lucas et al. 2007).