How Edmonton's city design changes the impact of heat waves

Although all Edmontonians are sweltering under the current heat wave, some are likely suffering more than others, says a University of Alberta researcher.

Cities are often hotter than rural areas because of the urban heat island effect: dense and paved infrastructure amplify and trap heat. 

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But the same things that cool rural areas – largely trees and other vegetation which provide shade, as well as bodies of water – can have a cooling effect in urban areas, too, or result in varying temperatures across a city when they are integrated into infrastructure design. 

In Edmonton, where the urban heat island effect means some parts of Alberta's capital city have been 12 degrees hotter than surrounding rural areas, both neighbourhood design and the North Saskatchewan River's orientation have an impact, urban and regional planning professor Sandeep Agrawal told CTV News Edmonton on Tuesday. 

"The south benefits from a vast ravine system and tributaries and creeks that have vegetation along them, so that helps a lot," Agrawal said 

"But we do see urban heat island effect in some of the newer neighbourhoods in south Edmonton where vegetation has been removed, trees have been removed, and they basically have been paved over." 

Concrete and asphalt are called low-albedo surfaces, meaning they absorb more heat than they reflect. 

"Essentially, they keep absorbing the heat and then they slowly emit that heat in the surrounding area. That then increases the ambient temperature than what it normally is," Agrawal explained. 

During a heat wave like the current one, he added, "The higher the temperature, the more heat is absorbed by these surfaces, and then they are eventually emitting more heat in the ambient area." 

Research done in the U.S. also suggests communities of colour or lower incomes are disproportionately affected by heat islands, partly the result of the American government's historic redlining practice. 

Urban heat islands present a "very serious problem" as global temperatures rise and more people die or are affected by heat exposure, Agrawal said. 

"The best way to mitigate the effect is to protect trees," he told CTV News Edmonton. 

Protecting trees could look like city bylaws that regulate trees on public property as well as private and citizens and developers refraining from removing vegetation and reducing the amount of low-albedo materials they use in design. 

With files from CTV News Edmoton's Connor Hogg