Solve for X: Innovations to Change the World

Soak it up: Can sponge cities save us from flooding?

Episode Summary

As the effects of climate change trigger record-breaking rainfall and flooding, cities from Montreal to Mumbai are re-thinking how urban design can keep inhabitants safe from natural disasters. Kongjian Yu, a landscape architect based in Beijing, has a counterintuitive idea. Instead of fighting water by building more dams, sewers and pipes, he proposes we let it in, designing nature-based infrastructure that can absorb run-off. His principles have been adopted by the Chinese government and implemented in hundreds of municipalities. Could this nature-based approach help us adapt to a changing climate?

Episode Notes

Featured in this episode: 

Kongjian Yu is a Beijing-based landscape architect and founder of Peking University’s College of Architecture and Landscape. His concept of sponge cities — designing cities to absorb water — is being applied in urban areas across the globe.  

Further reading:

Episode Transcription

Narration: Picture the common household sponge. You probably have at least a couple of these around your home. They’re pretty straightforward objects that do exactly two things: they absorb water, and they release it. Now, imagine the place that you live in, and what happens when it rains there. 

[sound of alarms and thunderstorms]

Narration: If, like me, you live in a city, much of that rainwater falls on roads, sidewalks and buildings before running into a massive sewer system. When it rains a lot, that infrastructure can get overwhelmed and our streets flood. And with climate change, that flooding is becoming much more frequent — and much more catastrophic. But what if the city functioned more like a sponge by your kitchen sink? What if all that rainwater got drawn in — by vegetation, by green roofs, by permeable pavement — and absorbed into the environment? 

For one thing, it would mean a lot less flooding. But it could also help solve other climate-related problems like excessive urban temperatures, carbon emissions and biodiversity loss. 

This sponge city concept is the brainchild of Kongjian Yu, a landscape architect and professor at Peking University in Beijing. Since he began his research 30 years ago, Yu has overseen the construction of hundreds of landscaped urban parks throughout China. They all operate on the same simple idea: give water more space. 

In other words, we have to stop fighting water — and learn to embrace it. 

I’m Manjula Selvarajah, and this is Solve For X: Innovations to Change the World, a series where we explore the latest ideas in tech and science. 

China has ambitious plans. It’s piloted the idea of sponge cities in 30 different places across the country, and it’s even adopted the principles into its template for urban design, incorporating soft materials and specialized design techniques like terracing, so that rain gets soaked up and slowed down by these so-called sponge cities, instead of accumulating in the streets. And the rest of the world is following suit. Sponge parks of various size and shape can be found everywhere from Malmö, Sweden to Montreal. These will be crucial in making our cities more resilient and able to cope with larger, more violent storms. 

 

Still, there are questions that remain. How do we get cash-strapped governments to change the way they’ve been building for over a century? And how much green space do we actually need to combat storms supercharged by climate change? On today’s episode, we talk to Kongjian Yu about the immense potential of sponge cities. 

Manjula Selvarajah: Kongjian, where have we reached you today?

Kongjian Yu: I’m here in Beijing. Beijing University campus.

Manjula Selvarajah: You’re on the campus right now.

Kongjian Yu: Yes, yeah.

Manjula Selvarajah: What’s the weather like today in Beijing? What is it like?

Kongjian Yu: It’s autumn in Beijing. It’s beautiful. It’s cool. It’s the best season of the year.

Manjula Selvarajah: Is it now? Thank you for joining us. We are really interested in this, in your idea of sponge cities. Now, there’s an experience in your childhood that inspired this work. Can you take us back to what happened to you when you were young? 

Kongjian Yu: So I was growing up in a small village in southern China’s Zhejiang province. It is a region of monsoon climate. So every year we have floods and in one year, I remember when I was about 10 years old, I fell into the flood — the creek. The creek, which would swell every year. And that year, I, by accident, fell into the river. But I survived because I grabbed all these willows and trees and shrubs and reeds along the river. That saved my life and that also became the inspiration for my idea about what a river should be, what a sponge city should look like.

Manjula Selvarajah: So talk to me about that. Can you walk us through your concept of sponge cities?

Kongjian Yu: So a sponge city is a nature-based solution. The idea is that the landscape or the city, and as a territory, should function like a sponge that can absorb — retain water and release water — when we are in a dry season. So it is a way of regulating water and also provides a habitat for biodiversity and it cleans the water. So it is a holistic solution, and a sponge city can also cool off the temperature because many of the cities today are suffering urban heat island. So if you have green sponge in the city, you actually cool off the city. Maximally, based on our data, we can reduce about 10 degrees of temperature during the summer in the middle of the city, in the central city.

Manjula Selvarajah: That’s a substantial, substantial amount. Now, you know, I look at the kind of cities that we have now, and a lot of our urban areas are structured to actually whisk water away, right? We have these hard, flat surfaces that steer the water towards the sewer. What are the problems with this approach that we have now, given the changing climate?

Kongjian Yu: Yes, that’s a serious problem we are facing today, globally, and the sponge city is trying to make a difference. It’s an alternative to this kind of grey infrastructure, which is made up of concrete, pipes and pumps and pavement. So this kind of grey infrastructure is based on industrial technology, and all urbanization happened based on this kind of grey infrastructure. Now, the problem with this grey infrastructure, number one, there’s no resilience for these kinds of concrete channels, steel pipes and pumps, so they’ll fail as long as you have unexpected precipitation. And they are originally invented in developed areas like London or European countries: the Netherlands, London, Paris. And when you look at this area, this early developed area, or early industrialized area, the climate was very mild…

Manjula Selvarajah: …And predictable. Mild and predictable. 

Kongjian Yu: Predictable and very mild, which every month you have the same amount, usually the same amount, of precipitation. So with climate change, this kind of infrastructure totally fails. That’s one problem. A second problem, when this kind of infrastructure is copied into the monsoon area such as China, India, Malaysia, Indonesia — usually these areas are underdeveloped, and they simply copy this industrialized infrastructure. That’s why most of these cities, Beijing, you know, Bangkok, Mumbai, Delhi or Jakarta — they all fail because simply they cannot adapt to this kind of monsoon climate, which means you have very dry seasons and you have very wet seasons. And from day one, from day one, this kind of grey infrastructure was not designed for monsoon climate. But today the whole world has become monsoon-like. You even see in New York, right? In London, we have suffering. Even in European countries, we are suffering monsoon-like climate situations. Global-wise, you can see any of the headlines of major newspapers every day. I mean, a couple days ago in Kenya, even in Abu Dhabi, you can imagine, in Abu Dhabi in Dubai, we have these floods, because we all built all this kind of grey infrastructure which has no resilience at all.

Manjula Selvarajah: This is the situation we have in Canadian cities, too, by the way, Kongjian. I mean, take Toronto, I live near Toronto as an example. We have these things we called 100-year storms, meaning it comes one in one every 100 years. But we’ve had three of those in the last decade already. So we are now seeing our highways get flooded, cars floating, people’s houses getting flooded out too. So I think the grey infrastructure that worked for our cities in Canada can’t handle them anymore, as well.

Kongjian Yu: That’s right. So we have two strategies to fix it. Engineers always think, or civil engineers really believe that if we keep investing in making a stronger and heavier and thicker pipe system, we can solve that problem. But that will fail again. I guarantee this kind of grey infrastructure, this kind of a mentality that “If we have more concrete, you have more stronger dams and dikes, you have more powerful pump systems we can adapt to this kind of climate.” Now that’s totally wrong.

Manjula Selvarajah: Now this is, this is what I find quite interesting about your idea. I mean, there’s a thought in there that is, actually is, a bit counterintuitive. I mean, your idea says we should, in some ways, let in the water and kind of embrace the water. Why do you think we need to make friends with the water? 

Kongjian Yu: In Chinese philosophy, water is the most soft thing. We usually compare water to ladies, to females, because they’re soft, they’re very kind, they’re very gentle. But actually, water is also the most forceful nature. No matter how strong you build your dams or your dikes, water will destroy it, because water needs space. If you push water to the corner like a beast, if you push the beast, for example, in Canada, you have grizzly beer. The grizzly beer, you cannot push the grizzly bear to the corner.

 

Manjula Selvarajah: Oh the grizzly bear, yeah, that is very true.

Kongjian Yu: That’s… but if you’re very gentle, very kind to the grizzly bear, you can make friends with that, right? Because it has potential power. Water needs space to come down, to nourish the ground, and to nourish the earth and to nourish the vegetation. I have a Canadian friend, a very, very famous journalist, Erica Gies. She has a beautiful book called Water Always Wins, right? Water always wins, no matter how strong you build a dam. So we all have the experience, you see New Orleans collapsed — the dam in New Orleans collapsed. And dams anywhere — I mean anywhere — no matter how powerful the dam is built, if you have too much water, it will collapse. Someday, once every hundred or once every thousand years, no matter how safe you want to make it, but when it collapses, it can kill thousands and thousands of people. That’s what we have experienced before, no one talked about it. I mean, we still trust that dams can protect us from flooding.

Narration: This idea hits very close to home for me, sadly. Just a few days before I spoke to Professor Yu, in the city where I grew up, Maiduguri, in northeastern Nigeria, heavy rains caused the nearby dam to collapse. Hundreds of thousands of people were displaced. This city is close to the Sahara Desert, and it’s unbelievable to me that there was a flood of any kind there, even from a dam breaking, because it’s practically the driest place that I can think of. 

Now to understand how this sponge approach works in comparison to traditional grey infrastructure, I wanted to get a sense of what a sponge city or a park could look like.

Manjula Selvarajah: Could you walk us through, you know, one or two of your projects, you know, either the Hou Tan Park in Shanghai or the Red Ribbon one in the Hebei Province? So that people get a… just kind of paint a picture for us, so people get an understanding of what it is that makes it a sponge, and not just another area in the city. 

Kongjian Yu: Yeah, so for example, in one of my projects, it’s a very recent project in Sanya City, in Hainan Island. It is a monsoon and tropical city. So I built a park right in the middle of the city, and I used a very simple solution: just cut and fill, cut and fill, so you create a porous landscape. So I created a lake, but the lake is distributed with hundreds of islands. And in each of the islands you can grow trees. 

Narration: OK, I had to see what this looks like. If you look up pictures of the park in Sanya City, it’s gorgeous. What you see are skyscrapers in the background, and the foreground? It’s just lusciously green. There are mangrove trees, there’s a lake with what looks like fingers of land. Within the lake are many man made islands, big and small, a field of blue polka-dotted with green. It’s kind of surreal. It looks like something out of a Dr. Seuss book, and then zig-zagging above everything is an elevated walkway.

Kongjian Yu: So during a flood, you can walk above the trees. During the dry season, you can walk under the canopy, and all these islands become a habitat for birds. So all kinds of birds come into the city because there’s a safe habitat. They can have nests, they have babies. And this park is only about, you know, 50 to 60 hectares. It can, it can regulate a million cubic metres of stormwater, so urban stormwater. 

Manjula Selvarajah: That’s substantial. 

Kongjian Yu: Eventually, you can reduce the urban runoff about 10 times as this area of this park. So which means, if you have 20 percent of green space functioning like a sponge within the city, you can virtually solve all the problems of urban floods. But certainly I’m talking about the regional scale. About national scale, when you imagine my little river, in my, back to my hometown that has green and blue together, so the whole system will become a sponge-like system, you know, regulating water.

Manjula Selvarajah: But you’re saying that it would need, for an urban city, you’re saying that it would take 20 percent of the city to be a sponge for us to address these issues?

Kongjian Yu: If, yeah…

Manjula Selvarajah: That’s a substantial… that’s a substantial amount.

Kongjian Yu: Well, it’s not a luxury amount. It’s not a luxury amount. Because every city, particularly in Canada, in American cities, you have a huge amount of green space. In Chinese cities, the regulation requires 30 percent of green space within a city. Well, in your suburb, I mean, in Vancouver, in Toronto suburb, you have, you know, 50 percent — more than that — of green space. So if you just transform a portion of this green space into a sponge, you can virtually solve the problem of floods at a regional scale, right? Your backyard becomes a sponge, your front yard becomes a sponge, your community garden can be a sponge, your roof garden can become a sponge, and your farm can be a sponge. Now, that’s totally opposite to what we have built today.

Narration: Sponges aren’t quite everywhere yet, at least not in Canada, but they’re becoming more and more common. In fact, my producer Ellie discovered a small example just down the street from her apartment. We were very curious to see it in action, so she grabbed her recording gear and went to see for herself. 

[sound of rain hitting pavement] 

Ellen Payne Smith: I’m standing in Montreal. It’s an October day. It’s finally raining — something I’ve been waiting for. And I’m here to witness how my local sponge pavement is working to absorb the water around the gutter. So I see a bunch of stones and some greenery, some flowers growing tall. And what it means is that while on the asphalt, water is pooling around and drip-dropping right by the sewer, there’s actually no water pooling around. It’s just getting absorbed by the greenery and by the rocks and draining into the environment. If I compare it to over here, there’s a puddle. 

[sound of Ellen stepping in a puddle]

Ellen Payne Smith: And then I stand over here, no puddle, just squishy, spongy feeling. 

[sound of Ellen stepping on wet grass]

Ellie Payne Smith: So yeah, this is an example of this sponge city on a very micro scale, just a few metres from my apartment. And uh, pretty cool!

Manjula Selvarajah: When I look at, when I see pictures of some of the things that you’ve built, first of all, they’re beautiful. I can understand why people who live in the area love walking through them and experiencing them, and why they’re award-winning, these parks. But when I look at the actual pictures, there’s also really a range of materials you’re using. I mean, you’ve incorporated nature, because you know that nature and reeds and grasses absorb water, but talk to me about these sponge solutions. How much of them are nature-based, and how much are sort of new materials and porous substances that you’ve discovered, or people are inventing? 

Kongjian Yu: For the Chinese culture, we have actually accumulated all these experiences —  the wisdom of how to deal with dry seasons, wet seasons of flood — because it’s a monsoon climate. So I learned from the farmer’s experience such as terracing the slope, pounding the ground, islanding when you have too much water and always build low weirs along the course to slow down water. Now these are the designs and technologies. So based on the technologies, you can use materials to slow down water, you use rocks to retain water, you create these terraces and permeable — even concrete can be permeable, OK? Stone can be permeable, right? 

And at the end, you design the building totally different, not design the river, design the building makes a difference, design the city makes a city itself different. For example, the height of the threshold, just raise the threshold, you will give water more space, right? So all these fairly simple technologies, they can be used for the creation of a sponge city. And remember, water is key for the whole ecosystem. So if you have water, if you can manage water, you will have a beautiful landscape. You don’t have to irrigate it, and certainly it’s become a beautiful place for people. And because people love this kind of space, the property value increased dramatically surrounding this sponge system, sponge park. In my case, we have most of our sponge system can increase property value double or triple, even. 

Manjula Selvarajah: I’m starting to see sort of there are threads of you trying to make a business case for it. 

Kongjian Yu: It is!

Manjula Selvarajah: And from that business, I want to take you to something that, something else that I found really compelling. You know, you’re not talking here about rebuilding, you know, Vancouver or Montreal, or any of our cities from the ground up. You’re talking about actually taking the city as it is and sponging up some of the areas. Am I right in that description? 

Kongjian Yu: Yes. 

Manjula Selvarajah: So are you saying that, I mean, if you look at most of the cities that we have in Canada and really around the world, you know, you have these really old sewers, you have a ton of asphalt, you have old park design, and also, also you have governments that are working with very tight budgets, and perhaps resistant to take all of that out, or resistant to put in new infrastructure. So how then, if the solution is to sponge up certain parts of the city, how do we do that, given that governments are so resistant to spending money these days?

Kongjian Yu: It’s not an issue about money, because it is an investment. It is not a cost. When you think about how much it will damage, how much a flood will damage our city, you will see that this kind of investment can get a return, maybe just one year or two years, or just one flood, OK? So in any case, you are going to invest in some kind of infrastructure. Now are you going to invest in the grey infrastructure again to fix a pipe system, to fix the concrete channels, or fix the flood wall, which will fail again? Or are you going to invest in this multifunctional green infrastructure? I call the ecological infrastructure, this sponge system. Now, so that’s about, that’s a mentality, that you invest, maybe only a quarter of that money you plan to invest in concrete, you can fix the problem. 

So based on my experience, the cost is much, much less by investing in green infrastructure than investing in grey infrastructure. So let’s make it clear: You have to protect the city, or you have to solve the problem. The problem is there, the tiger is outside. The tiger is at your doorway. So are you going to make friends with a tiger? Or, or grizzly bear is maybe a more good example. Are you going to make friends with a grizzly bear? Or are you going to attack the grizzly bear to make it more dangerous? So that’s about your question about budget, about invest. It is, as I said, it is not a cost, it is an investment because it will save your cost. That’s number one. Number two: you really have to make a movement to create a new culture. It is a revolution, OK? It is a revolutionary change from industrial civilization to ecological civilization. We have to change as a culture, yeah? If we keep trusting this concrete, we’ll never fix it. 

Manjula Selvarajah: Wow. [laughter] I can tell, I can tell you feel very, feel very strongly about this. You know, I will have to say, Professor Kongjian, I… I, one thing that I do like about the idea is that you’re not suggesting that we remove the grey infrastructure that we have already. What you’re suggesting is you keep that grey infrastructure, but instead of spending on new and larger grey infrastructure, you create these sponge areas and sponge parks around and in our cities, which I think, I think that there is a real collaborative feel here, that I, that I really like.

Kongjian Yu: Yeah, I think it is collaborative. So you are right, you are right. So green and grey can be together, right? You, I don’t, I don’t mean we want to wipe it out — everything built, OK? It’s built. But as they will say, they are going obsolete, they can decay, you know? Any concrete, every 100 years later, they will fail anyway, right? They will fail anyway. So that’s why, gradually, incrementally, we can transform the city into more nature-based. Because when we change as a mindset, understand how nature can function, how nature can become infrastructure, we can, you know, transform it gradually. But radically, in some cases, we need also a revolutionary change. Now that must be from the political, political policy-makers. You need from mayor to even prime minister, even president of the nation to think about that, because world climate change is already such a serious issue, serious problem today. Now we need to adapt to it, all right? 

Mitigation, of course, we’re going to reduce carbon emissions, but adaptation becomes immediate. It is a crisis. Now you will see 100-year occurrence, but the next year it will happen again. Urban heat — an energy issue, OK? The biodiversity is an energy issue. So what’s a holistic solution? Concrete cannot be a holistic solution. Any industrial technology cannot become a holistic solution, because from day one it was invented, it only has one single goal. It never takes care of biodiversity, it never takes care of urban heat, it never takes care of the ecosystem. The only one single goal is to flush away water, flush away flood, keep the water outside, and eventually the groundwater will die out, the groundwater will dry out, and the sea level will keep rising. You know why sea level keep rising? 40 percent of seawater comes from the ground, from the dry out of the groundwater. So you have a flood. But at the same time, the more serious problem is drought. Canada, you have so much water. Of course, you have the richest country in the world in terms of water resources. But global-wise, we are in a shortage of water. We only have one water. So if the whole world dries out, Canada will dry out.

Narration: Climate change has never just been one problem. It’s many cascading issues coming together — a polycrisis, to use the increasingly-popular term. And if that’s true, then we need a multi-level, holistic solution to address all these things at once. As Professor Yu points out, that might be the key to help cities survive. 

Manjula Selvarajah: You’ve described your approach to designing landscapes as an art of survival. Why do you think we need to think about survival as an art form?

Kongjian Yu: Engineering is to solve problems by single-minded engineering work, it can be ugly, it can be ugly. And survival is usually not what landscape architecture concerns. Landscape usually concerns about beauty. So I combine these two together. It is about survival, because we are suffering flood, we are suffering drought, we are suffering fire, we are suffering urban heat. Now that survival, the modern city is actually more sensitive to all these kinds of climate change. We are becoming more and more vulnerable to the natural disasters because we are more centralized. As an advanced human civilization, beauty is certainly so important. So landscape provide holistic services, including provide beauty, including provide inspiration, spiritual inspiration, as well as the regulation of water, as well as providing food, as well as supporting biodiversity. So landscape is about designing a human habitat for all human needs. 

Manjula Selvarajah: Thank you so much, Kongjian. Thank you for speaking with us today. 

Kongjian Yu: My pleasure. 

Manjula Selvarajah: Good luck. And what do you have coming up next? 

Kongjian Yu: Well, next, I want to transform the planet into a sponge planet. [laughter]

Manjula Selvarajah: A sponge planet!

Kongjian Yu: Yes. 

Manjula Selvarajah: Do you have an estimate, an ETA for that, when that’ll get done? 

Kongjian Yu: Well, I think it may be as fast as maybe 20 years we can, we can fix the problem. 

Manjula Selvarajah: OK, sponge planet in 20 years, I’m going to call you then. 

Kongjian Yu: Yes. Good, good. 

Manjula Selvarah: Thank you. Thank you so much, and have a good night.

Kongjian Yu: Thank you.

Narration: Kongjian Yu is a professor and founding dean of Peking University College of Architecture and Landscape. He’s also the author of the book Letters to the Leaders of China

Solve for X is brought to you by MaRS. This episode was produced by Ellen Payne Smith and written by Jason McBride. Lara Torvi and Sana Maqbool are the associate producers. Mack Swain composed the theme song and all the music in this episode. Gab Harpelle is our mix engineer. Kathryn Hayward is our executive producer. I’m your host Manjula Selvarajah. Watch your feed for new episodes coming soon.

Solve for X is brought to you by MaRS, North America’s largest urban innovation hub and a registered charity. MaRS supports startups and accelerates the adoption of high-impact solutions to some of the world’s biggest challenges. For more information, visit marsdd.com. And we want to hear from you — drop us a line to share your ideas, questions and feedback. What innovations are you curious about? What changes would you like to see in your urban environment? Email us at media@marsdd.com.