Banff National Park, Alberta, Canada - wildfire

Eight worst wildfire weather years on record happened in last decade

Image credit: London School of Economics

Lower humidity and higher temperatures are driving extreme weather that makes wildfires more frequent and intense, say experts.

The world’s eight most extreme wildfire weather years have occurred in the last decade, according to a new study from researchers at the University of Alberta, Canada. The study suggests that extreme fire weather is being driven by a decrease in atmospheric humidity coupled with rising temperatures.

“Extreme conditions drive the world’s fire activity,” said Michael Flannigan, a former University of Alberta wildfire expert, who conducted the research with study lead Piyush Jain, a research scientist with Natural Resources Canada, and Sean Coogan, a postdoctoral fellow at the Faculty of Agricultural, Life and Environmental Sciences.

Flannigan continued: “For example, in Canada, just three per cent of fires are responsible for 97 per cent of the area burned.”

For the study, the team examined extreme fire weather trends from 1979 to 2020 using common fire weather indexes that provide estimates for fire intensity and rate of fire spread, as well as changes in vapour pressure, or humidity.

The results link trends in rising global temperatures and decreases in humidity to the likelihood that naturally occurring extreme fire events will happen more often, spread to new areas and burn more intensely than ever before in recorded history.

Decreasing relative humidity was a driver of more than three-quarters of significant increases in intensity and fire spread, while increasing temperature was a driver for 40 per cent of significant trends.

The study also found significant increases in extreme weather that can cause major fires in close to half of the Earth’s burnable land mass - including in Northern Canada and British Columbia.

Flannigan said regions around the world have almost universally witnessed an increase in extreme weather in the past 40 years, with marked increases in the last two decades.

“It's not a big surprise," he added, "but with climate change we expect warmer conditions to continue and this trend to continue, expand and get worse.”

In British Columbia, for instance, Flannigan said three of the last five fire seasons — 2017, 2018 and 2021 — are the three worst on record.

Living with wildfire also means living with the consequences of fire. The recent flooding that is crippling land travel in and out of British Columbia's lower mainland is a good example.

“It is not all attributable to fires, but fires do play a role," Flannigan said. "When you remove the vegetation, the rain is not being intercepted by the trees; the roots aren't picking up the moisture; there is nothing to give the soil stability — you're much more likely to see land and mudslides in burnt areas.

“This has been documented in California for years.”

Flannigan noted that even if global warming stopped tomorrow, the wildfire threat would continue to loom large for decades, so communities need to prepare for all wildfire eventualities.

“We're on this path of a new reality. It's not normal because there's nothing normal about what's going on.”

The study - Observed increases in extreme fire weather driven by atmospheric humidity and temperature - has been published in the journal Nature Climate Change.

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