Cities are overheating. How do we cool them down?

September 7, 2024 Canuck

Quirks and Quarks54:00Overheated – a Quirks & Quarks special about urban heat

It’s getting hot in here, especially if you live in a big city, as most Canadians do. And with cities getting warmer than ever, experts say it’s time to make our cities cooler.

“I think all of the answers exist right on our doorsteps, and we just have to work together to make it happen,” said Melissa McHale, an associate professor of urban ecology at the faculty of forestry at the University of British Columbia in Vancouver.

The warming planet means heat waves will be more intense and more frequent, and that heat is amplified in cities, due to the urban heat island effect.

That’s the name given to describe when cities trap and radiate heat, making them several degrees warmer than the surrounding countryside.

“Much of this higher temperature is because of the fact that urban areas tend to have surfaces like concrete and asphalt,” said Sandeep Agrawal, a professor at the School of Urban and Regional Planning and the director of the Alberta Land Institute at the University of Alberta in Edmonton.

“They absorb a lot of solar energy, and then they release it in the air over time.”

But it’s not just those surfaces. Big buildings, packed closely together block the wind and trap the heat.

While the solutions take time, says McHale, there are changes that can be made to cool cities down.

Two people look at a dog while seated on rocks near a body of water, while a passenger ferry passes by. Another person is also sitting by the rocks looking away from the camera. — People are pictured during a period of hot weather near False Creek in Vancouver, B.C., on Thursday June 20, 2024. (Hunter Soo/CBC)

The dangers of overheating

Agrawal and his team studied temperatures in Toronto, Vancouver, Edmonton, Calgary and Montreal using satellite images that record land surface temperatures in the cities and surrounding rural areas.

He found that urban areas were often six to 12 degrees hotter than rural areas, with the highest urban heat islands in Toronto and Vancouver.

Agrawal says there needs to be more trees which absorb heat over time, and less concrete. He also suggests larger buildings have what are called green roofs, which would have vegetation or water to reflect and soak in some of that heat.

Green roof with both green and yellow grasses on the Vancouver Convention Centre pictured in 2018 — Green roofs, like this one seen on the Vancouver Convention Centre in 2018, can help reduce temperatures of the roof and surrounding air. (Denis Dossman/CBC)

Agrawal says some municipalities are making strides. He says Toronto has enacted strong protections around the cutting down of trees, as well as the implementation of green roofs.

James Voogt, a professor of geography and environment at Western University in London, Ont., says it’s pretty clear that these are important issues for cities to tackle.

“If you look at all of the environmental factors, I like to call them the ways that weather can kill you, heat is number one,” said Voogt. “It’s been underreported in the past but it’s of growing concern.”

Between 2000 and 2020, roughly 670 deaths were attributed to extreme heat events in Canada’s 12 largest cities, according to a report by Statistics Canada released in June.

A single heat-dome event in British Columbia in 2021 killed an estimated 619 people over one week, according to the B.C. Coroners Service.

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What are people doing?

Making buildings more resistant to heat is exactly what Robin Hawker does. She leads the engineering and consulting firm Introba Canada’s climate risk and resilience practice.

One of the projects she’s working on is the future St. Paul’s Hospital in Vancouver, which is being rebuilt near False Creek after more than a century on Burrard St. downtown. One of the major climate hazards she looked at for the project was extreme heat.

“We looked at … what are the maximum temperatures that the building could realistically face over the next 50 years?” said Hawker.

“With climate change, we expect those maximum temperatures will be increasing notably. And so we want to make sure that the mechanical systems, and the ventilation systems, and all of the materials in the building are designed to stand up to those future temperatures.”

From the early stages of design, they made sure the building was positioned to minimize the amount of sunlight that would hit the windows. They also added thicker insulation and higher-quality windows.

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The hospital also has 17 different green roof areas, to absorb heat, and uses lighter-coloured roof pavement.

“This really is what we call a passive approach to extreme heat management, where you’re preventing the increase in heat within the building without using any mechanical strategies or energy,” said Hawker.

“This would be considered a climate resilient strategy.”

But it will take more than just adjusting how we build to make cities more resilient, according to McHale. Each part of a city needs to be examined.

She says the city of Vancouver has opened up creeks that used to be covered. Not only does the stream make the city more beautiful, but it also helps cool the city down, says McHale. Some of the solutions can be as simple as adding more trees.

WATCH | Bringing back a once-covered stream in Vancouver:

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The Vancouver Park Board has unveiled a small segment of a restored historical stream. Originally known as ‘First Creek’, it flows through Volunteer and Tatlow parks on the city’s West Side. As Rob Easton reports, it’s meant to clean the city’s runoff, while also reconnecting people to the natural shoreline.

She says it’s also important to look at cooling the places where people congregate in a city, such as bus stops.

“A lot of people are standing in one location, waiting for public transportation, and people can get really hot and uncomfortable while they’re waiting for the bus,” said McHale.

“If you’re looking for places to mitigate heat, why not choose places that can impact a lot of people at once?”

Marathon, not a sprint

Whatever a city does, McHale says there isn’t a one-size-fits-all approach. And that goes for not just the city, but each individual neighbourhood.

“Every neighborhood has a different context, has a different set of challenges that they’re facing,” said McHale.

For example, many poorer neighbourhoods tend to have fewer parks and less green space, and therefore less shelter and cooling.

And while McHale says there is no question these solutions need to be considered right now, it also can’t be rushed.

“This is the conundrum. The world is heating up, our cities are heating up. But the solutions for that take time. And I don’t think that the quick solutions are the best solutions,” said McHale.

“If we can invest in these kinds of local solutions and help people make the most out of the spaces around them, then our cities are going to be climate resilient in the future.”

A graphic image, primarily coloured purple and red, shows a city skyline beneath a bright, radiating sun. The text reads Overheated, with the letter O stylized as a thermometer.

This story is part of our Overheated series, a collaboration between What on Earth, Quirks & Quarks, and White Coat, Black Art, that explores how heat is affecting our health, our cities and our ecosystems.

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