What’s causing the ‘heat dome’?

A thermometre against a sunny orange sky By VladisChern/Shutterstock

An extreme heat event has broken records in the Pacific Northwest this summer. The highest temperature ever recorded in Canada occurred in Lytton, B.C. The town reached a high of 49.6˚C before being consumed in a human-caused fire. The heat threatened both infrastructure and human health on the western coast as hundreds of heat-related deaths were attributed to the extreme weather. The situation illustrates the urgent need for communities to plan and adapt for extreme heat waves, as climate change will increase the frequency of these events in the future.

The extreme heat event was caused by a meteorological phenomenon called a “heat dome.” “The ‘heat dome’ is a neat analogy for a pretty common meteorological phenomenon known as blocking,” says Christopher Fletcher, an associate professor with the University of Waterloo’s Department of Geography and Management, and a member of the university’s Interdisciplinary Centre on Climate Change.

Blocking is a phenomenon that affects the jet stream: a fast-moving current of air circulating west-to-east around the northern hemisphere that divides colder Arctic air to the north from warmer tropical air to the south, says Fletcher. The jet stream isn’t a straight line across the continent. “The jet stream has wiggles in it, known as waves, that affect whether the prevailing weather is coming from the north, a cold air mass, or the south, a warm air mass,” Fletcher explains. “This recent heat dome was caused by a particularly persistent ‘wiggle’, or blocking event, that stayed centred on the Pacific Northwest for several days, and caused sinking air that trapped all the warmth near the surface. It got incredibly hot, like completely unprecedentedly hot for that region, on par with some of the very hottest places on Earth, like the Middle East and Australia,” Fletcher adds.

Blocking events can happen anywhere you’ve got a division between warm and cold air and waves in a jet stream, says Fletcher. “They are quite common, but seldom so severe as this event.”

Fletcher says that weather prediction models can predict a heat dome event up to a week in advance. But a week-long heads-up isn’t enough time for communities to prepare for an extreme weather event like the one seen in the Pacific Northwest. “The problem is that the places affected by this event are not used to extreme heat like this, and so predicting it is one thing, but the infrastructure just isn’t geared up to cope with an event of this magnitude.”

10 tips for coping with wildfire smoke

Western University’s Gordon McBean, a professor emeritus with the Department of Geography & Environment and the director for policy at the Institute for Catastrophic Loss Reduction (ICLR), says that communities need to adapt to reduce their vulnerability exposure to extreme weather events caused by climate change.

The ICLR produces straightforward guides on how homeowners can protect their property from climate change-related weather events like flooding, extreme heat, and fire. (The guide on protecting a home from wildlife was created by the ICLR in association with FireSmart Canada. Among its recommendations is the advice to store firewood piles away from the home. It also notes that certain plants are more fire-resistant than others; wildfire resistant trees include poplar, birch, and maples.)

“Cottage country is nice because you have all the nice trees next to you,” says McBean. “But if your cottage is built in a way that you have vegetation right up close to it and things are drying, then that’s a way that fire can be propagated from a wildfire to the house.”

Taking proactive steps now to protect your cottage from heat-related events is important because these events will continue to occur into the future. Fletcher says that we’ve already seen an increase in the number and intensity of extreme heat events in Canada, and all the science is pointing, with high certainty, to even more severe and frequent events in the coming decades.

“We are heading toward a new normal,” says Fletcher. “We need to act now.”

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