Bushfires and extreme heat in south-east Australia

Bushfires and extreme heat in south-east Australia. By David Karoly
Real Climate, February 16, 2009 @ 3:12 PM

Guest commentary by David Karoly, Professor of Meteorology at the University of Melbourne in Australia

On Saturday 7 February 2009, Australia experienced its worst natural disaster in more than 100 years, when catastrophic bushfires killed more than 180 people and destroyed more than 2000 homes in Victoria, Australia. These fires occurred on a day of unprecedented high temperatures in south-east Australia, part of a heat wave that started 10 days earlier, and a record dry spell.

This has been written from Melbourne, Australia, exactly one week after the fires, just enough time to pause and reflect on this tragedy and the extraordinary weather that led to it. First, I want to express my sincere sympathy to all who have lost family members or friends and all who have suffered through this disaster.

There has been very high global media coverage of this natural disaster and, of course, speculation on the possible role of climate change in these fires. So, did climate change cause these fires? The simple answer is “No!” Climate change did not start the fires. Unfortunately, it appears that one or more of the fires may have been lit by arsonists, others may have started by accident and some may have been started by fallen power lines, lightning or other natural causes.

Maybe there is a different way to phrase that question: In what way, if any, is climate change likely to have affected these bush fires?

To answer that question, we need to look at the history of fires and fire weather over the last hundred years or so. Bushfires are a regular occurrence in south-east Australia, with previous disastrous fires on Ash Wednesday, 16 February 1983, and Black Friday, 13 January 1939, both of which led to significant loss of life and property. Fortunately, a recent report “Bushfire Weather in Southeast Australia: Recent Trends and Projected Climate Change Impacts”(ref. 1) in 2007 provides a comprehensive assessment on this topic. In addition, a Special Climate Statement(ref 2) from the Australian Bureau of Meteorology describes the extraordinary heat wave and drought conditions at the time of the fires.

Following the Black Friday fires, the MacArthur Forest Fire Danger Index (FFDI) was developed in the 1960s as an empirical indicator of weather conditions associated with high and extreme fire danger and the difficulty of fire suppression. The FFDI is the product of terms related to exponentials of maximum temperature, relative humidity, wind speed, and dryness of fuel (measured using a drought factor). Each of these terms is related to environmental factors affecting the severity of bushfire conditions. The formula for FFDI is given in the report on Bushfire Weather in Southeast Australia. The FFDI scale is used for the rating of fire danger and the declaration of total fire ban days in Victoria.

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