On February 7, 1967, a series of fires spread across part of the Australian state of Tasmania, combining into a firestorm that, over the space of a few hours, killed 64 people, injured 900 more, and left thousands homeless.
Conditions were ripe for the disaster. The previous spring had experienced heavy rainfall that had produced a massive growth in vegetation which then effectively became kindling when the wet spring was followed by an abnormally hot summer. The fires might not have had such an immense human impact, David Bowman of the University of Tasmania told the Independent, were it not for the fact that "plonking cities in front of a highly flammable vegetation type is a recipe for disaster."
Fifty years later, it's a lesson that needs to be relearned, according to a study led by Bowman and published in the journal Nature Ecology & Evolution.
Extreme fire events are, Bowman noted, "a global and natural phenomenon," but the combination of land use and a changing climate is creating conditions in which they can become more common and have more devastating human impact.
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Using data from NASA satellites, Bowman and his team compiled a massive database of 23 million landscape fires between 2003 and 2012. Of these, they selected 478 especially severe fires, from which they isolated 144 as being economically and socially disastrous extreme fire events. These were concentrated in regions where humans have built into flammable forested landscapes, such as areas surrounding cities in southern Australia and western North America.
Fully 96 percent of these disastrous fire events were associated with anomalous meteorological conditions such as high temperatures, winds, or fire danger; or extreme climate conditions such as drought or, in arid areas, extremely high rainfall producing high levels of vegetation that can then act as fuel - the conditions that precipitated the Black Tuesday bushfires.
"It's a little like Goldilocks, if you will: if it's too dry, you won't have sufficient vegetation, and if it's too wet, you don't have the fuel to power the fire," said John Abatzaglou of the University of Idaho, a co-author of the paper. "But somewhere in between, it's just right. And then you wait for the right combination of drought and high fire danger, so the environment is very much enabling the possibility for these large fires. And then you just wait for an ignition source and potentially some wind."
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The study found that disastrous extreme fire events appeared less common around the Mediterranean than in the western United States or southeastern Australia, despite having a similar climate. The researchers suspect one likely reason is the Mediterranean landscape is more heavily managed, while the bushlands of Australia and the US are more likely to be left to grow.
But due to changes in climate conditions, the researchers predict more frequent extreme fires in the Mediterranean, as temperatures increase and humidity declines during the summer fire season.
They also anticipate a greater susceptibility to fires in the subtropical Southern Hemisphere, the southwestern U.S. and Mexico, largely due to decreased spring rainfall.
They calculate that there will be an average 35 percent increase in the number of days per year of high fire danger across global land surfaces by mid-century.
"The projections that we look at for climate change suggest that we will more often see conditions that have historically been conducive to these large fires," Abatzaglou said. "Climate change, across most of these flammable biomes, is basically going to increase the seasonal windows when fuels will be receptive to significant fires. It acts as a threat multiplier. And over the long haul, people are likely to be moving into some of these areas, including much of the western United States."
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