By Tim Radford
The conditions for extreme and catastrophic wildfires could increase by 20% to 50% as the world warms and the climate changes, according to new research.
An analysis of 23 million wildfires between 2002 and 2013 has identified 478 of the worst – scientists call them “extreme wildfire events”.
“Extreme fire events are a global and natural phenomenon, particularly in forested areas that have pronounced dry seasons,” says David Bowman of the University of Tasmania in Hobart, Australia, who led the study with US colleagues.
Weather for wildfires
“With the exception of land clearance, the research found that extremely intense fires are associated with anomalous weather – such as droughts, winds or, in desert regions, following particularly wet seasons.
“Of the top 478 events, we identified 144 economically and socially disastrous extreme fire events that were concentrated in regions where humans have built into flammable forested landscapes, such as areas surrounding cities in southern Australia and western North America.”
It follows a series of warnings of increased wildfire hazard as global temperatures rise in response to the ever greater levels of greenhouse gases in the atmosphere, as a consequence of the increasing combustion of fossil fuels.
Fire poses a threat to the entire warming world. US authorities spent more than $2bn suppressing wildfires in 2015, but greater conflagrations are expected in the US west, and wildfire damage could eventually double, according to other studies.
But the hazard is not confined to the Americas. The researchers began their analysis to identify the range of conditions that turn a chance lightning bolt, or a carelessly discarded cigarette, into the kind of conflagration that kills people and destroys townships. And they found a pattern: in more than nine out of 10 cases, “anomalous” weather conditions made the hazard worse.
These could be high winds, high temperatures and drought, and, in desert regions, unusually high rainfall the preceding season that triggers greater growth and more fuel for the next fire.
“Climate change is causing fire seasons to start earlier and finish later, with an associated trend towards more extreme wildfire events in terms of their geographic extent and duration, intensity, severity, associated suppression costs, and loss of life and property,” the scientists write.
The sharpest increases will be on Australia’s east coast and in the Mediterranean basin, in particular Portugal, Spain, France, Greece and Turkey. Some of these landscapes are naturally adapted to fire. But in the US, a higher proportion of all fires became disasters for precisely identified reasons.
“What makes a fire event a disaster in the US is when key factors combine – low-density housing amidst dense forests, the right climatic conditions and a lack of fire preparedness on the part of humans,” says co-author Crystal Kolden of the University of Idaho in the US.
“We can’t stop big, intense fires from happening here, and they are increasing under climate change. However, in the western US, we can reduce the potential for fire disasters by both reducing forest density and improving mitigation and preparedness through the development of fire-resilient communities.”