Two years ago, floods devastated large swaths of Pakistan. Architect Yasmeen Lari has been a pivotal figure in facilitating the recovery, working with displaced residents to rebuild their homes. But, as flooding becomes more commonplace around the world, Lari believes it is necessary to look beyond disaster response, and harness design in proactive ways to reduce the risk.
“Every country, every city is now facing more or less this kind of issue — whether it’s New York or London or Karachi,” says Lari. “So we all need to prepare for it.”
The past few months have seen severe cases of flooding in countries including Nigeria, India, China, Bangladesh, the US and Germany, caused by high-intensity rainfall and overwhelmed infrastructure. Experts believe climate change will only continue to exacerbate the frequency and intensity of rainstorms. Many are scrambling for solutions to reduce their impact, to better protect people, homes and infrastructure. One of those solutions: making cities and homes “spongier”.
In Karachi, Lari — the country’s first female architect, now 83 years old — is delivering a programme of “Climate-Smart Eco-Streets”, as part of the non-profit organisation, the Heritage Foundation of Pakistan. It takes a street-by-street approach to protecting the city from flooding and adapting to climate change. At Denso Hall Rahguzar, the pilot project on a shopping street in Karachi’s historic heart, she has installed terracotta pavements that absorb water, pocket gardens of trees and stormwater wells, alongside other interventions that help reduce pollution and heat intensity.
Underpinning the project are the principles of the “sponge city” — a concept popularised by Chinese landscape architect Kongjian Yu that, over the past decade, has gained traction. Through nature-focused landscaping, cities are made more able to absorb and retain water, reducing surface run-off and decreasing flood risk.
Yu — founder of the landscape architecture firm Turenscape, and professor at Peking University — last year won the Cornelia Hahn Oberlander International Landscape Architecture Prize for the idea. While the concept may be a future-facing strategy, it is inspired by traditional landscape management techniques to preserve water. “The sponge city concept adapts these ancient principles into urban planning,” says Yu, “by incorporating permeable surfaces, green spaces, and constructed wetlands.”
Yu’s concept was adopted by the Chinese government in 2013 following increased flooding, and subsequently tested in a pilot programme across 30 cities. In Sanya, a city on China’s Hainan island, Yu and his team created a large-scale park that naturally manages water to prevent flooding. Concrete flood walls — which had damaged biodiversity — were replaced by sponge-like wetlands, terraced embankments, ponds, rice paddies and greenways that can reportedly accommodate 830,000 cubic metres of stormwater, intermingled with pedestrian and bicycle paths for resident use. Yu calls it “an exemplary model” of sponge city implementation — around 200 mayors have visited it for inspiration — and Turenscape has delivered similar projects from Xi’an to Chongqing.
But despite the sponge city idea’s global ripples of influence, it is rare for such flood resilience strategies to be joined-up and citywide. As with most requirements to adapt to climate change, the scale of the problem — and the response needed — can be overwhelming, causing progress paralysis. Although governmental policy is vital, can a street-by-street, or neighbourhood-by-neighbourhood approach catalyse wider changes?
In the drive for greater permeability, concrete is the first villain to tackle. “Everybody has got to stop using concrete,” insists Lari. “That is the worst material. It actually causes more flooding. If you look at urban flooding, the reason why it’s becoming worse is because we’ve got concrete paving everywhere. Water is not able to seep into the soil.”
When intense rainfall hits concrete pavements, car parks, buildings and public spaces, it has nowhere else to go, forced to run off into drains, sewers and rivers that can become inundated. In a sponge city, however, surfaces such as terracotta, brick, open-joint paving, gravel and porous asphalt allow water to soak through to a sub-base where it is slowly released into the ground — replenishing aquifers — or into drains in a manageable flow. In her Karachi project, Lari uses terracotta tiling to replace impervious concrete pavers — absorbing water while also bringing a natural tonal warmth to the streetscape.
Cities around the world that long looked to concrete as a robust way to build have begun to embrace more permeable surfaces. In Denmark, Tredje Natur (Third Nature) has developed a perforated “climate tile” which works to absorb more rainwater. In New York City — where an estimated 70 per cent of the city is covered in impervious materials — flood resilience has been particularly high on the agenda. Work started this summer on the installation of seven miles of porous pavement in Brooklyn to reduce flooding by preventing millions of gallons of rainwater flowing into the sewers.
Plants, too, play a central role in improving permeability, absorbing water while also improving air quality, tackling extreme heat and boosting biodiversity. “Right in the middle of streets, we should plant forests,” says Lari. This is what she has been doing in Karachi, installing mini forests in her eco-streets project. Lari was inspired by a method popularised by Japanese botanist Akira Miyawaki, who looked to the rapid creation of small-scale forests to naturally restore degraded land.
Specially designed planted basins and ponds, known as bioswales or rain gardens, are another sponge tactic, acting like micro-wetlands in periods of heavy rainfall, capturing stormwater and surface run-off before letting it slowly drain away or absorb into the ground. These can work harder than greenery alone: organisations including the Royal Horticultural Society suggest that rain gardens can absorb 30 per cent more water than lawns.
In New York, new developments with impervious surfaces are required to integrate features such as rain gardens, trees and porous pavements to help manage stormwater and prevent flooding. Thousands of kerbside rain gardens are also being created across the city.
Over in New Jersey, the city of Hoboken opened the ResilienCity Park in 2023, a green space that can detain up to 2mn gallons of stormwater during heavy rainfall, including a basketball court that doubles as a stormwater detention basin.
Design interventions to make Los Angeles spongier have included “green alleys”, specially designed pedestrian thoroughfares that combine permeable pavements with bioswales and gardens to absorb and retain stormwater. Such efforts seemed to prove successful this February, when amid historic rainfall on the city, 13.5bn gallons of stormwater were captured, reportedly enough to serve nearly 165,000 households for an entire year.
But it’s not just about landscaping: buildings can play their part in reducing flooding too. While green roofs — rooftops covered in a bed of plants — help improve air quality, absorb water and cool buildings, blue-green roofs go one step further by mixing a layer of plants with a system of rainwater storage. This enables the water to be kept on the roof and reused to sustain the plants, or even satisfy building needs such as flushing loos.
In Amsterdam, the EU-supported Resilio project created over 12,683 sq m of blue-green roofs on social housing complexes across four city neighbourhoods, with residents engaged in the process. While some of the rooftops are fully covered in plants, others integrate paths and seating for residents to enjoy the space, blending flood resilience with leisure.
Inevitably, implementing the sponge city is not without challenges. Much of the landscaping approach involves replacing concrete infrastructure with greenery, posing financial and practical challenges. “[It] requires changing existing regulations, building codes, and practices, which can face resistance from stakeholders accustomed to conventional methods,” says Yu. In London, Mayor Sadiq Khan’s proposals to tax those who pave over gardens, as set out in July’s London Climate Resilience Review, drew ire from those with private driveways.
Both practically and politically, then, it can be easier to integrate sponge city principles from the start in the design of new neighbourhoods — and Berlin, Vienna and Leeds show such ideas coming to life. The German capital’s decommissioned Tegel airport — once the city’s primary international flight hub — is undergoing a large-scale, €8bn transformation into a new district comprising the residential Schumacher Quartier and a campus for students and businesses called The Urban Tech Republic. Providing more than 5,000 homes, the largely car-free Schumacher Quartier is designed to be resilient to the impact of accelerating climate change — and is planned on the basis of the sponge city model.
In the neighbourhood, rainwater will be retained in bioswales or courtyard pools, where it can sustain greenery or be used for residential plumbing. Other permeable surfaces will allow rainwater to seep into the ground, while buildings will feature green roofs and walls. The first residents are expected to move in from 2028 or 2029.
In Vienna, a similar story is unfolding. Seestadt Aspern, one of Europe’s largest urban development projects, is transforming a decommissioned airfield into the seeds of a whole new urban quarter. One of its neighbourhoods, Am Seebogen, is heralded as the largest sponge city project in Austria. Already home to 6,500 residents and planned to house 12,000 more, it features extensive tree cover, supported by subterranean chambers that capture and store rainwater, making it available for sustaining the vegetation in dry spells.
Meanwhile in Leeds, a 516-home “Climate Innovation District” is taking shape, which mixes low-carbon buildings and pedestrianised streets with extensive green infrastructure and flood-resilient drainage. Homes feature green roofs and rain gardens, while paving is permeable, and rainwater detention basins across the development manage stormwater.
Such examples require sizeable investments, but action can be taken by individuals too. “Small-scale adaptations can be made at the neighbourhood or even household level,” says Yu, highlighting the benefits of installing green roofs and walls, permeable driveways or walkways, rain gardens, and rainwater storage and reuse systems. “These implementations not only contribute to the overall resilience of the urban environment but also engage residents in sustainable practices, fostering a culture of environmental stewardship.”
The sponge city may not be delivered all at once, but perhaps project by project, pore by pore, it can emerge from collective efforts.
This community aspect is at the forefront of Lari’s approach in Karachi. She knows that public involvement is crucial in realising and maintaining her eco-streets, especially in lieu of top-down funding.
“No government will have enough money to be able to really take up the challenges that exist today because of climate change,” she says. “But everything can be taken care of.”
She is now working on two more eco-streets. “I don’t know what will happen in a few years time, because the intensity [of rainfall] keeps on increasing, but at least for the foreseeable future, we can prevent urban flooding,” she says, highlighting the sponge-inspired designs such as porous pavements and street forests. “This can be done locally. And it should be done.”
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