Joni Mitchell was right – they are really paving the way for paradise and setting up parking lots.

Statistics Canada’s first survey of urban green space shows that, as the singer-songwriter warned, cities across the country are getting grayer and browner.

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“We have seen a decline over the period we have been looking at,” said Jennie Wang, who helped draft a massive report from the federal agency released this month on human activities and the environment.

StatCan used satellite imagery to estimate the amount of green space in Canadian cities – parks, urban trees, even backyards and lawns. The data has been around for years, but it has been used for this purpose.

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“(We get) a sense of the state of vegetation in urban areas,” Wang said. “This is the first time we are doing this.”

The researchers looked at 31 urban centers of different sizes across the country. They compared satellite images from 2001, 2011 and 2019.

They found that about three-quarters of large and medium-sized cities in 2019 were less green than they were 20 years earlier.

“You end up seeing less green when you walk down the street,” Wang said.


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Big losers include cities like Kelowna, BC, which went from nearly three-quarters green to less than half. Milton, Ont., Experienced a similar decline, as did Winnipeg.

Toronto, Montreal, Vancouver, Calgary and Edmonton all lost green space. Saskatoon and Regina were among the few who won.

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Urbanization is a major driver of loss of green space, Wang said. Milton grew by 350 percent over the course of the study and Kelowna’s population grew from 150,000 to 223,000.

Other factors such as drought or insect infections also play a role. Winnipeg’s losses, for example, were exaggerated by the emerald ash drill.

But the losses are real, Wang said, and have real implications.

“There are studies that show the many benefits of vegetation,” Wang said. “There is a reduction in energy consumption, trees remove air pollution. “There is also research looking at human health benefits.”

Green spaces also reduce what are called urban heat islands – high-temperature bubbles around cities.


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Sandeep Agrawal, a geographer and urban planner at the University of Alberta, found the temperature difference between a city like Edmonton and the surrounding countryside can be as high as five or six degrees. That differential is linked to the amount of urban green.

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“As tree cover declines, the urban heat island effect increases considerably,” he said.

Heat islands can help cause human health problems such as respiratory failure or heat stroke, a problem that has been exacerbated in heat waves such as those experienced over much of western Canada last summer.

The BC coroner’s office identified 569 heat-related deaths between June 20 and July 29.

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There is no return once a pasture or forest site has been repelled for homes or shopping malls, Agrawal said. Even when the landscape matures, it does not completely replace what was there before.

“You can never do that,” he said. “It’s just not possible.”

Governments are beginning to recognize the issue, he said, making it more difficult to cut down trees on public land and enact laws that promote so-called “green roofs,” vegetation planted on top of buildings.

Most Canadians live in cities, Wang said. She said her research could help governments find out how their policies affect the trees and grass that live next to urban concrete and asphalt.

“This kind of information can help cities monitor whether there is an effect of their policies.”

© 2022 The Canadian Press



Reference-globalnews.ca

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