'Sponge cities': An absorbing idea in the face of climate change
From China to Montreal, urban planners are using nature to solve problem of flooding
At the bottom of a slope in a dense Montreal neighbourhood, there's a new park with benches, an open field and a playground — along with two small pedestrian bridges.
When there's heavy rain, water rushes down the streets and sidewalks into the green space, forming a small lake beneath the overpasses, in a carved-out area filled with grasses, shrubs and rocks.
In the days that follow, the water slowly seeps into the soil and stormwater system. It's all been engineered to prevent flash flooding in nearby streets and homes, while nourishing the vegetation in the park.
"Instead of seeing the rain as something bad, we are now keeping the rain and turning it into something beautiful," said Philippe Sabourin, a spokesperson for the City of Montreal, on a recent tour of the area.
As is the case in most cities, Montreal's drain systems are overwhelmed — and its streets and homes flooded — by torrential rains made more frequent by climate change.
Pierre Danserau Park, built in 2019 on the grounds of an old rail yard, is one of seven "sponge parks" across the city.
This fall, the city announced plans to build 30 more, in an attempt to curb flooding and keep flood water — which mixes with sewage when the city water system is under strain — out of the St. Lawrence River.
From grey to green
Similar spongy approaches to water management have taken hold elsewhere, from green rooftops in Toronto to lakes and wetlands alongside housing developments in Berlin.
Kongjian Yu, a Chinese landscape architect, pioneered the concept. Inspired by the way his childhood village coped with flooding during the monsoon season, Yu has made green solutions to water management his life's work.
He has overseen the re-imagining of 20 "sponge cities" in China, with elaborate changes to infrastructure making way for more green spaces that can absorb water and keep the city cooler during heat waves.
Yu's vision goes far beyond a scattering of parks. His sponge cities feature vast stretches of green and blue, where ponds and wetlands are allowed to co-exist with highways and highrises.
The approach is well-suited to China, where the monsoon season routinely floods many cities. He said the traditional urban infrastructure "made of pipes, made of concrete, made of pumps" has no "resiliency at all" in the face of heavy rain fall.
In a Zoom interview from his office in Beijing, Yu described the approach as the total opposite of "conventional grey infrastructure."
"It is a fundamental change. It is an evolutionary change of the relationship between man and nature," he said.
Sponges, where they makes sense
In Canada, a greener approach to water management is also getting increased consideration as municipalities begin thinking "more creatively" about urban planning, said Alexandra Lesnikowski, head of the climate adaptation lab at Concordia University in Montreal.
"Increasingly, what we're discovering is that a lot of the systems that were built decades ago are no longer sufficient to help keep us dry and safe in a changing climate," she said.
Lesnikowski said the effectiveness of a sponge park or any other green infrastructure depends on the details — that is, the location and the design.
"We don't yet have ... really large, robust evidence based on what works where and what the limits of these types of interventions are for dealing with especially larger-scale climate risks," she said, adding that municipalities need to be "careful and strategic" in determining which projects to invest in.
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