Climate change supercharged a heat dome, intensifying 2021 fire season, study finds – The Mercury News

Alex Wigglesworth | Los Angeles Times (TNS)

Three years ago, as a massive heat dome towered over the Pacific Northwest, swaths of North America simmered, then burned. Wildfires have charred more than 18.5 million acres across the continent, with most of the land burned in Canada and California.

A new study has revealed how human-caused climate change intensified this extraordinary event, with researchers theorizing that the heat dome was 34% larger and lasted almost 60% longer than it would have been in the absence of global warming. The heat dome, in turn, was associated with up to a third of the area burned in North America that year, according to the study published in Communications Earth & Environment.

“What’s happening is the weather is stagnating: it’s very hot and very dry,” said study author Piyush Jain, a research scientist at Natural Resources Canada. “And that dries out all the vegetation and makes everything on the ground extremely flammable.”

The study adds to a body of literature documenting how the fingerprints of climate change can be detected in events such as heat waves, droughts and wildfires.

Jain was living in Edmonton in late June 2021 when the mercury in North America’s northernmost city of a million people topped 100 degrees. “I was blown away,” he said. “I had never experienced these temperatures anywhere I had lived.”

Further south, the town of Lytton, British Columbia, experienced Canada’s hottest temperature ever recorded at 119 degrees on June 29, and was largely destroyed by a wildfire the next day.

The heat dome persisted for 27 days, from June 18 to July 14, with temperatures soaring across the western United States and Canada, killing hundreds of people, leading to mass die-offs of marine life , devastating agricultural and forestry yields and damaged infrastructure. , the closure of highways in Washington and the melting of electric train lines in Portland. Over a five-day period in June, locations in seven U.S. states, including California, exceeded all-time maximum temperature records, according to the National Oceanic and Atmospheric Administration.

The heat wave also increased fire risk, breaking numerous fire weather records over a wide area and helping to fuel fires in British Columbia, California, Arizona, Colorado, Utah and Montana . More than 7.9 million acres burned in North America in July alone — at that time, the largest area in a single month since record-keeping began, the study found. Smoke swept across the continent, triggering air quality alerts across much of the East Coast.

Jain had previously worked with other researchers to develop a method for assessing such extreme weather events by examining anomalies in geopotential heights, which indicate whether there are high or low pressure systems in the upper atmosphere. High-pressure systems that persist for a long period of time tend to correspond with heat waves and increased fire risk, he explained. And climate change has contributed to an increasing trend, potentially amplifying these events.

In this study, Jain and his colleagues analyzed what the thermal dome would have looked like without this trend. They estimated that it would have been 34% smaller, 59% shorter and its magnitude would have been 6% lower.

Researchers also found strong links between extreme heat and wildfire activity in 2021. That year, 21% of burned land in North America was ravaged by fires that broke out during and at inside the heat dome, with that figure rising to 34 percent when taking into account fires that started within 10 days, the researchers found.

The size of the thermal dome made the situation particularly troubling, because it led to what the study authors called widespread synchronous combustion, with many disparate areas igniting at the same time. This has posed a challenge for fire departments, as they tend to seek help elsewhere when they do not have enough resources locally.

“If other regions are also experiencing the same pressure on their resources, you may encounter a bottleneck at some point,” Jain said.