How a sponge approach can help build more climate-resilient cities

Heat domes, wildfires, droughts – Canadians have first-hand experience of the effects of climate change on our weather. And from British Columbia to the Atlantic provinces, this also includes heavier and more frequent rains, flooding communities across the country.

Meanwhile, our cities and water management infrastructure are designed for an era when heavy rainfall was considered a once-in-a-century event.

“We build bigger buildings and leave less greenery around buildings because we’re going for maximum density,” said Ron Schwenger, president of Architek, a design-build company that has been a leader in living architecture for 15 years. “That also means more surrounding hardscape — pavement and concrete.”

When it rains, it pours

In the past, lawns, gardens, parks and meadows did some of the heavy lifting after a downpour, absorbing water into the ground. But as concrete jungles get bigger, excess water has nowhere to go. “All the rain is deflected into the storm sewer system, which can only absorb so much water,” Schwenger says.

With more intense downpours occurring more frequently, these systems are becoming overwhelmed, creating a dire need for creative new solutions to reduce the Flood.

For Schwenger, containing this rising tide means making building surfaces absorbent. “The more spongy a city is, the better it is at managing water during a heavy rainstorm,” he says.

Creating a sponge effect

The so-called sponge city approach does not mean that dishwashing aids are integrated into urban design. Rather, it builds on another climate change mitigation tactic — the green roof — to absorb and use rainwater, essentially turning hard surfaces into sponges.

“Planted material can seep through and hold water, just like miniature sponges,” Schwenger says. “When it rains, green roofs and green spaces absorb water instead of diverting it to storm sewers.”

While the idea of ​​green roofs evokes beautiful gardens and vegetation, the benefits of such living architecture run much deeper. “Ten to 15 years ago, cities focused on shallow green roofs. But now we see a big push for high-capacity green roofs, or what we call blue-green roofs,” says Schwenger.

Blue-green roofs consist of a water collection system up to 15 centimeters deep, topped with soil and plants. “It’s like a small shallow pond and the use of wicking agents and devices means the water is passively irrigated into the soil and to the plants,” he explains. While a shallow green roof can contain 10 to 20 liters of water per square metre, blue-green roofs absorb as much as 90 liters per square metre.

Green roofs mean healthier cities

The benefits of green roofs go well beyond flood prevention. “With all the high-rise buildings, cities become gorges of glass and concrete,” says Schwenger. “With fewer parks and nature reserves, the temperature will rise significantly and the air quality will decline. Green absorbs carbon dioxide and releases oxygen, and is mission critical to keep cities cool and livable.” Green roofs are also vital for pollinators, which in turn protect food supplies, he adds.

Schwenger looks at places like Amsterdam, where the entire green roof system is connected to a digital grid, to illustrate its full potential.

“The roofs have hatches that are centrally controlled. If they have had a special rainy season and the rivers and canals are high, they trap all that water on the roofs. But if they have a drier period and the rivers are low, then they can drain that water.”

Here in Canada, Schwenger says, “We’re a long way from that.” But with the millions of dollars earmarked for urban greenery in the most recent federal budget, and the statutes and strategies promoting green roofs in cities like Toronto and Vancouver, Schwenger says the potential is huge — as long as the approach is more than superficial. .

“Just building a green roof is not enough,” he says. “We need standards for water retention and other metrics to make sure these roofs don’t just look green — they could actually help us fight climate change and its impacts.”

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