Normal text size Larger text size Very large text size Sydney experienced its first ever day of catastrophic fire danger in November, and fires have continued to rage and spread to more parts of Australia's south-east – with no end in sight. Multiple blazes have stretched fire services to their limits. A choking haze forms a backdrop to life in Sydney, Canberra, regional towns and lately, Melbourne. In short, the situation has been described as dire. So is there a link between climate change and more severe and frequent bushfires? The aftermath of fire in Rainbow Flat near the Pacific Highway on November 9. Credit:Dean Sewell How do scientists measure fire danger? The likelihood of hostile extreme weather can be measured in a range of ways. For bushfires, scientists look at the McArthur Forest Fire Danger Index, developed in the 1960s by CSIRO scientist A.G. McArthur to forecast how weather would affect fire behaviour.


As the name suggests, the gauge examines the risks to woodlands from fire using a combination of rainfall or drought conditions along with predicted wind speeds, temperature and relative humidity. Typically, winter and spring see the highest ratings on this fire danger index in the north and these move southwards as spring makes way for summer. How bad is catastrophic then? Fire and emergency authorities started to review response plans in 2008 to adjust to "the growing intensity and severity of recent bushfire experiences across the country". Then Black Saturday's bushfires erupted in Victoria on February 7 in 2009, leaving 173 people dead. That event "brought into sharp focus the possibility that the current legislation, systems, practices and processes to support effective community safety outcomes may no longer match the increasing levels of risk and expectations", a bushfire warning taskforce report noted. The highest fire danger rating was set as "catastrophic" for index readings of 100 or more. (In Victoria, they are dubbed Code Red.) The basic message was boiled down to: "For your survival, leaving is the best option." The dire assessment is because some fires on such days are likely to become "uncontrollable, unpredictable and fast moving" and "there is a very high likelihood that people in the path of the fire will die or be injured", the taskforce said.


Melbourne reached an index reading of about 150 on Black Saturday, according to Ross Bradstock, director of the Centre for Environmental Risk Management of Bushfires at the University of Wollongong. For Sydney to exceed 100 on the index could be a first, at least for its Observatory Hill and Sydney Airport sites, where the weather is measured. Does climate change play a part? Yes, there is a link between climate change and the prevalence and severity of fires. In fact, the research identifying a link between fires and climate change is "old hat", says Professor Bradstock. "The research has all been done. We don’t need to keep doing it." As the Bureau of Meteorology and CSIRO pointed out in last year's latest State of the Climate report, the number of the most extreme 10 per cent of fire weather days based on the fire danger index "has increased in recent decades across many regions of Australia, especially in southern and eastern Australia". "There has been an associated increase in the length of the fire weather season," it said. "Climate change, including increasing temperatures, is contributing to these changes."


Or, as Hamish Clarke, a former NSW government scientist and now with the University of Wollongong, puts it: "Across the country, at a number of high-quality long-term weather stations, there had either been an increase, or no change [in the fire danger index]. We didn’t find a significant decrease anywhere." In general, one consequence for fire authorities is that the fire season is getting longer. In eastern Australia, that means fire risks start to increase earlier in the spring and last longer into the autumn. The window for hazard-reduction burning is shifting into winter – if it's not too damp to do it. How human activity and natural climate variability factored in bushfire ratings increases from 1973 to 2017 was the focus of research by Sarah Harris, from the Victoria's Country Fire Authority, and Chris Lucas in September. Firefighters north of Forster near the junction of the Pacific Highway on November 8. Credit:Dean Sewell While rainfall changes from one year to the next, with phenomena such as El Ninos in the Pacific and shifting Indian Ocean conditions playing a role, the researchers' findings were conclusive: "We propose that anthropogenic [human-led] climate change is the primary driver of the [upward trend in the fire danger index], through both higher mean temperatures and, potentially, through associated shifts in large-scale rainfall patterns." How unusual is this year?


Depending on where you are, very unusual. NSW, for instance, could see a million hectares burned so far this fire season within days – if it hasn't already done so. That is about the same as the past three fire seasons combined – and summer is yet to arrive. Rainfall deficiencies – or what most of us call "drought" – are already the worst on record for northern NSW and parts of southern Queensland. And it has also been hot. According to the Bureau of Meteorology, Australia posted its hottest January-October in records going back to 1910 for maximum temperatures. It looks like only a cool spell, which is not on the forecast charts, will stop 2019 being the hottest year on record for daytime readings. Loading Of particular concern for this week is how very dry areas are around big population centres such as Sydney, Newcastle and Wollongong. Temperatures are likely to reach the mid- to high 30s on November 12 at a time when moisture levels in plants – a gauge of how quickly they will burn if fire breaks out – are tracking below those of the big fire season of 2013 in the Sydney area, and the worst since 2002.


Professor Bradstock published research in 2009 that predicted how the fire danger index would track to 2030 and 2050, using CSIRO data from 2007. "The current predictions [for Sydney on November 12] are beyond what we predicted back in 2007," he says. "That's not good." The Hillville fire on November 8. Credit:Dean Sewell