Smoke rises from a wildfire burning at Jasper National Park on July 24.Supplied/Getty Images
In the aftermath of the devastating wildfire that destroyed one-third of the town of Jasper, Alta., two weeks ago, Parks Canada says it has been working with wildfire researchers to understand how the disaster unfolded and what it may portend for communities battling future extreme fires.
It took less than three days from the time the Jasper wildfire started until it engulfed the town. As investigators come to grips with the shocking speed of events, one of the questions they face is what role pyrocumulonimbus clouds, or pyroCbs, played in accelerating the worst fire in the park’s 117-year history.
These towering storm clouds are the byproducts of extreme wildfires and meteorological conditions. Driven by intense heat, air rises rapidly above the fire, creating a chimney effect. When it encounters colder air higher up, the atmosphere can become unstable, causing downdrafts and a vertical circulation that is similar to what happens inside a classic thunderstorm.
The air rising at the centre of the formation can send smoke and burning embers upward and outward for many kilometres.
While the phenomenon has been recognized for years, pyroCbs have more recently become a focus for wildfire researchers because their occurrence in fire-prone regions appears to be growing – nowhere more than in Canada.
“Canada seems to be the global hot spot,” said Richard Carr, a fire research analyst with the Canadian Forest Service, based in Edmonton. “We probably had about 80 per cent of the world’s pyroCbs last year and in a lot of years we tend to have the most.”
While pyroCbs only form in a small fraction of Canadian wildfires, those fires tend to be the most destructive.
The cause of the Jasper wildfires still remains under investigation. Eyewitness accounts and other observations suggest it was started on July 22 by multiple lightning strikes to the north and south of the town, which sits at an intersection point of mountain valleys running through Jasper National Park.
Indigenous communities face harsher effects from wildfire smoke
In the south, three fires merged and rapidly advanced toward the town, aided by strong winds moving in the same direction. That wind, with gusts estimated at 125 to 150 kilometres an hour, “far exceeded forecasts,” Michelle Macullo, a fire information officer with Parks Canada, told The Globe and Mail.
By July 24, the north and south fires were joined and the town was in flames, only one day after some 25,000 residents and visitors were evacuated.
Satellite imagery and other evidence from Jasper suggest that two pyroCbs formed as the fire grew.
“In the grand scheme of pyroCbs, they weren’t huge,” said David Peterson, a meteorologist with the U.S. Naval Research Laboratory in Monterey, Calif. However, he added those storm systems could still have affected the progress of the fire.
This conclusion is supported by additional evidence from the ground.
One photo of the Jasper fire, posted on the park’s Facebook page on July 24, shows a bright, white cloud reaching up above columns of billowing smoke as the leading edge of the fire approaches the deserted town.
Mike Flannigan, a fire weather scientist and professor at Thompson Rivers University in Kamloops, said that while it is not possible to be completely certain based on a single photo, the white cloud is “probably the top of the pyroCb.”
As a pyroCb develops, it can start new spot fires in the surrounding area, either through embers drifting back to the ground farther afield, or through lightning generated within the storm cloud itself. PyroCbs are also associated with erratic winds that generate thick clouds of smoke, reducing visibility and making the fire harder to see and combat on the ground and from the air.
All of this is of concern to analysts who use computer models to forecast fire behaviour. Once a pyroCb is in the mix, a fire can become less predictable, and its rate of spread is less likely to be reflected in models designed to show how fire moves across a particular landscape driven by external winds and fuel availability.
Even so, there’s no question those other factors still played a big role in Jasper. A study published last year in the journal Natural Hazards ranked the town third on a list of Alberta communities most at risk from wind-driven fires.
According to Jen Beverly, a fire researcher at the University of Alberta who co-authored the study, the fire that blazed its way into Jasper was aided by a continuous path of flammable fuels combined with hot, dry conditions and extreme winds. In short, she added, “a perfect storm played out.”
The question is whether the pyroCbs associated with the Jasper fire pushed this volatile combination even further off the charts of expected behaviour and what that means for other communities who are taking preventative measures and preparing emergency plans.
To better address such questions, Dr. Peterson and colleagues recently launched a five-year NASA-funded study that will include flying aircraft into and over pyroCbs to characterize their behaviour.
The team is in active discussion with Canadian officials to establish one of its sites in Cold Lake, Alta., or a similar northern location where aircraft bristling with sensors can be quickly deployed to study a developing pyroCb as early as the summer of 2026.
Dr. Peterson said the results will be important for those living well beyond Canada’s fire zones because the largest pyroCbs can elevate smoke to a level where they are taken up by high-altitude winds and then spread for thousands of kilometres.
In some cases, pyroCbs can send material up to the stratosphere where they can interact with the ozone layer and produce large-scale effects on the global climate. This was documented in research on pyroCbs that formed over Canada in 2017 and over Australia in 2020.
Contrary to expectations, last year’s record-breaking Canadian wildfire season – which included 123 pyroCbs – did not have the same impact, according to a new study by an MIT-based team that is still undergoing peer review.
“It’s still not clear why that is,” said Selena Zhang, a doctoral student who led the study.
Dr. Peterson said such results illustrate the point that the study of pyroCbs and their impact are still in their infancy, even as they become more prevalent in a warming world.
For Dr. Carr, pyroCbs also highlight the urgent race under way in Canada between fire scientists using the latest computational and observation tools to understand the complex nature of wildfire and a global climate change driving fire behaviour into novel territory.
“One of the challenges is trying to outpace the changes,” Dr. Carr said.