A heat wave is building across the Prairies and climate change means we can expect more

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A heat wave is building across Alberta, British Columbia and Saskatchewan this week, with temperatures forecasted to exceed 30 C, triggering heat warnings as far north as the Mackenzie Valley in the Northwest Territories.

With climate change, heat waves are becoming more frequent.

But how normal is a heat wave at this point in the summer?

And after last year's deadly heat dome, how does this one compare?

What's behind this late summer heat?

Heat has been building under a ridge in the United States and now is pushing into Canada.

As a strong area of high pressure builds in the west, temperatures are heating up and will continue until at least the end of the weekend.

Kyle Fougere, a meteorologist with Environment and Climate Change Canada, says the length of this heat wave is thanks to a pattern set up across the country, with high pressure and heat over the west, and low pressure over the east.

"Because there is a little bit of a blocking pattern with that strong low pressure system in the east, it is going to last a fairly long time," Fougere says.

As our ridge of high pressure sets up over the west, temperatures have the chance to get warmer and warmer, he says. 

"This heat builds day after day because these regions of high pressure have sinking air. They have these clear skies. And so you just get multiple days of clear skies and warming."

Heat waves and climate change 

We should get used to heat waves as we continue to feel the effects of climate change.

While the frequency of cold snaps is not as well known, our heat waves are getting more frequent. 

According to the Intergovernmental Panel on Climate Change's report on the changes on climate extremes, the length or number of warm spells or heat waves has increased since the middle of the 20th century.

And that trend that looks to continue. 

"It is very likely that the length, frequency, and/or intensity of warm spells or heat waves will increase over most land areas," the report says.

A year after the deadly heat dome

As we see more frequent heat events with climate change, the question of severity comes into play, especially a year after June 2021's unprecedented heat event.

The heat dome in 2021 led to the deaths of 619 people in B.C. It broke all-time heat records for Canada, as temperatures jumped well over 40 C.

Fougere says it is normal to think of heat events in the context of recent extremes. 

"That historic heat event of last year is certainly in everyone's mind because of all the impacts … the lives that were lost and the fires that occurred and all the records that were set," he says. 

Despite that memory, Fougere says that heat events like the one we are seeing this week are normal. He says we may see a few local records falling, but he's not expecting any all-time Alberta records to fall.

"To have a ridge of high pressure move over Western Canada and last for several days bringing temperatures into the low 30s is extremely common."

This summer has been slightly unusual because it began on the cool side, especially in Alberta. Fougere says that July acted as a switch in conditions.

"Ever since about the middle of July is when we started to see temperatures rebound. We are having a much different second half of summer."

And when it comes to August, Fougere adds that even though average temperatures generally peak in July, 30 C temperatures are the most common in August. 

Heat makes fires harder to control

Heat waves can raise red flags when it comes to fire danger in Canada. 

So far this season, Saskatchewan has had 325 fires, on par with the five-year average. Alberta has seen 819 fires.

Derrick Forsythe, a provincial information officer with Alberta Wildfire, says that while there have been fewer fires so far this year compared to 2021, the area burned is larger.

To date last year, 1,123 wildfires in Alberta had burned 53,920 hectares. This year, the province has seen 819 wildfires that have burned 107,517 hectares.

Forsythe says fire risk varies depending on where you are in the province, as some areas have had more rain in the past few days. 

This week, fire risk is high to extreme in the southern Prairies and in much of B.C., moderate for much of northern Alberta and Saskatchewan, and elevated in N.W.T.

Heat waves can elevate the risk of fires starting, and also make them harder to control. 

"If the temperature exceeds the relative humidity in an area, that means it's really dry and it's going to stay really dry," Forsythe says.

"If a fire starts, it's going to burn really quickly and spread really fast because it's just so hot and so dry. There's no residual moisture … in the atmosphere or on the ground to help mitigate that spread." 

After the wave breaks

Fougere says heat waves like this can often be followed by another extreme: severe storms. 

"When we have that high pressure break down and that low pressure system go through, it's able to tap into all that heat and energy that's built up and release the severe thunderstorms."

Those thunderstorms can pose risks for flooding, especially if the soil is extremely dry. 

Miles Dyck, a professor of soil science at the University of Alberta, says that in an extreme drought, drier soils can become hydrophobic — resistant to absorbing water.

"And if there's just too much precipitation … depending on the surface topography, it will run off to lower elevations," he says.

Though the south remains in drought conditions, the risk of soil becoming resistant to water is pretty low with this heat wave for the most part.

Despite the lower risk, Dyck says there are ways for you to help out your garden. 

"Maintain cover on your soil, either as a live vegetation canopy or as some kind of mulch. That will certainly protect the soil from drying out."

Our planet is changing. So is our journalism. This story is part of a CBC News initiative entitled "Our Changing Planet" to show and explain the effects of climate change. Keep up with the latest news on our Climate and Environment page.