How the 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 heavy and frequent rains, which inundate communities across the country.

Meanwhile, our cities and water management infrastructure are designed for an era when powerful rainstorms were considered a once-in-a-century event.

“We build bigger buildings and leave less space around the buildings because we strive for maximum density,” says Ron Schwinger, president of Architek, a design and construction firm that has been at the forefront of living architecture for 15 years. “It also means more solid slab surroundings – pavement and concrete.”

When something hits you, it can get tough

In the past, lawns, gardens, parks, and lawns did some heavy lifting after it rained, sucking the water into the ground. But as concrete forests expand, there is nowhere for the excess water to go. “All the rain deflects the sewage system, which only takes so much water,” Schwinger says.

With more powerful rainstorms occurring more often, these systems become overwhelmed, placing a high imperative on new creative solutions to reduce flooding.

For Schwinger, stopping this rising tide means making the roofs of buildings more absorbent. “The more spongy a city is, the more it can manage water during heavy rain,” he says.

Create a sponge effect

The so-called sponge city approach doesn’t mean incorporating dishwashing tools into urban design. Instead, it relies on another tactic to combat climate change – the green roof – to absorb and benefit from rainwater, turning hard surfaces into sponges.

“The implants can seep and retain water just like a miniature sponge can,” Schwinger says. “When it rains, green roofs and green spaces absorb the water rather than diverting it into the storm sewer system.”

Although the idea of ​​green roofs evokes beautiful gardens and plants, the benefits of this living architecture are much deeper. 10 to 15 years ago, cities were focused on shallow green roofs. But we are now seeing a widespread push for high-capacity green roofs, or what we call bluish green roofs, Schwinger says.

The bluish green roofs consist of a water harvesting system up to 15 cm deep, with soil and vegetation on top. “It’s like a small shallow pond, and through the use of wicking fabrics and devices, the water is irrigated passively into the soil and into the plants,” he explains. While a shallow green roof may hold 10 to 20 liters of water per square metre, bluish green roofs absorb up to 90 liters per square metre.

Green roofs mean healthier cities

The advantages of green roofs go beyond flood prevention. “With all the higher elevations, cities are turning into valleys of glass and concrete,” Schwinger says. “With fewer parks and natural spaces, there is a huge increase in temperature and a decrease in air quality. Green spaces absorb carbon dioxide and release oxygen, a critical task for keeping cities cool and livable.” He adds that green roofs are also essential for pollinators, which in turn protect the food supply.

Schwenger looks to places like Amsterdam, where the entire green roof system is connected on a digital network, to demonstrate the full potential.

“The roofs have trapdoor valves that are controlled from a central location. If they have a particularly rainy season and the rivers and canals are high, they keep all that water on the roofs. But if they have a dry period and the rivers are low, they can release that water.”

“We’re nowhere near that,” Schwinger says here in Canada. But with millions of dollars allocated to urban green space in the latest federal budget, and regulations and strategies promoting green roofs in cities like Toronto and Vancouver, Schwinger says the potential is huge — as long as the approach is more than superficial.

“Just putting in a green roof is not enough,” he says. “We need water retention standards and other metrics to make sure these surfaces not only look green – they can actually help us combat climate change and its effects.”

Learn more about green roofs at

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