Heat and drought caused 2023 fire season, study finds

The largest study of Canada’s catastrophic 2023 wildfires concludes it is “inevitable” that extreme heat and drought caused the record-breaking season, while the amount of young forests burned could make recovery more difficult.

The study warns that the extreme temperatures observed last year were already equivalent to some climate projections for 2050.

“It is inevitable that extreme heat and moisture deficits allowed the record-breaking 2023 wildfire season to occur,” reads the study, which was published Tuesday in the journal Nature Communications.

During the 2023 wildfire season, 150,000 square kilometres of forest were consumed by flames, seven times the historical average. Some 232,000 Canadians were forced to flee their homes, while 5,500 firefighters from around the world, national resources and the military were needed to battle the blazes. Smoke spread as far as Europe.

“In 2023, we had the most extreme fire weather on record across much of the country,” observed Piyush Jain, a scientist with Natural Resources Canada.

“I think the connection is pretty clear.”

According to the study, although the 2023 fire season did not play out the same way in different parts of the country, the underlying causes were the same everywhere.

This season has seen more extreme wildfire weather conditions — defined as a combination of heat and dryness that exceeds 95 percent of all days during the fire season — than any other year since records began in 1940.

Across the country, temperatures averaged 2.2 degrees above normal during the fire season.

But while the fires in the West were fueled by a years-long drought, Quebec suffered from a relatively new phenomenon known as a “flash drought.”

“This area was not in drought,” Jain noted. “It went into drought very, very quickly.”

The study emphasizes that flash drought is an “emerging process that we are only beginning to understand.”

Lightning also to blame

The study found that long periods of hot, dry weather were compounded by areas of high pressure that blocked the movement of air normally driven by the jet stream, a high-altitude river of air that encircles the planet and determines much of Earth’s weather.

Most places in Canada experience an average of 14 days under such stationary high pressure systems. In 2023, areas that suffered the worst fires experienced up to 60.

Additionally, many of these “blocking events” in the West occurred early in the season, accelerating mountain snowmelt and increasing the length of time forests were vulnerable to fire.

“It was caused by these large-scale weather events,” Jain said.

Moreover, widespread dry weather has contributed to larger fires than ever before. Although 834 large fires occurred in 2023, just 60 of them were responsible for nearly three-quarters of the area burned.

Only 7% of the burned area was affected by human-caused flames. Lightning was responsible for the rest.

Young forests in danger

The fires also affected more than 10,000 square kilometres of forest that had already burned over the past three decades.

“This disturbance is likely to cause significant tree regeneration failures after fire, as immature trees cannot provide sufficient seed after fire,” the study reads.

Thus, some areas could permanently transform into grasslands or other ecosystems. Previous research has shown that boreal forests have transformed into deciduous forests or shrublands after being affected by several fires.

“If a young forest is not at the stage where it would spread naturally, these species could be eliminated from the landscape,” Jain warned.

The study indicates that more than 3,000 square kilometres of commercial forest in Quebec are now vulnerable to “regeneration failures”.

This new study adds to other research that has found that climate change is making conditions favorable to fires up to three times more likely.

The combination of extreme heat and drought in 2023 could be a harbinger of things to come, Jain said. Climate models suggest that under the most extreme carbon emissions scenarios, these conditions could be normal by 2050.

“By mid-century, we’ll be seeing the same weather patterns we had in 2023 on a regular basis,” he said. “That would mean more of these big fire seasons.”

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