Like a desert needs rain: Turning floods to friends with sponge cities 

There’s a scene in the Simpsons where Bart complains about the heat to his father, Homer Simpson, saying: “This is the hottest summer of my life.” Homer wags a finger at Bart and corrects him: “This is the coldest summer of the rest of your life.”

As with so much of what the Simpsons have unleashed upon the world, this too has the ring of bitter truth: every year temperatures climb to unprecedented levels and, thanks to the vagaries of climate change, the hotter the world gets, the wetter it gets – especially in places where a great deal of rain wasn’t exactly a norm; places like Dubai and Saudi Arabia, for example, both of which saw torrential rains this year. 

The rainfall was so severe that even the best urban infrastructure could not deal with it; Dubai, which typically receives only 97mm of rain a year was suddenly inundated with over 250mm of rain in a 24-hour period. That’s the kind of rain that even the wetter cities of the world, with drainage systems designed to handle large amounts of rainwater, would be hard-pressed to handle and as a result Dubai faced massive urban flooding.

The costs of implementing such projects can be huge, but they are dwarfed by the clear costs of inaction.

- Zarrar Khuhro

It didn’t help that traditionally dry Dubai – the population and size of which has ballooned in recent decades – saw little need for a comprehensive drainage system even as the city itself expanded simply because no one expected this level of rain. The massive expansion of Dubai in and of itself was another problem, as the sand that usually could absorb the rainfall had been paved over with concrete leaving the water nowhere to go by blocking natural water absorption systems. This also means that underground aquifers do not replenish the way they should; natural waterways are also blocked, exacerbating the problem.

Similarly, the eastern province of Saudi Arabia also saw torrential rain causing roads to turn into rivers in Dammam, much like what happened in Jeddah the previous two years. Again, we see that the lack of an effective drainage system commensurate to the way these cities have been growing in size, exacerbated the urban flooding.

Dubai is, of course, now throwing vast amounts of money at the problem and is planning to expand its sewage and drainage systems, but this may not be as effective as imagined if done in isolation.

What may prove to be a better and more holistic solution is to marry such efforts with the concept of ‘sponge cities’, an idea that is increasingly in vogue among engineers with a mind toward sustainability and adaptability. Rather than trying to simply drain away the water, sponge cities aim to absorb excess rainfall and then release it over time much like a sponge does. 

Professor Kongjian Yu, “the sponge cities architect’ explains it like this: “We can make friends with floods. We can make friends with water.” This is done by increasing the number of green spaces in a city and letting such spaces act as natural flood absorbers. On a micro level, these include rain gardens — depressed areas in the landscape that collects rain water from a roof, driveway or street and allows it to soak into the ground. These can be planted with grass or flowering plants or even serve as small-scale community gardens or urban farms where locals can grow fruits and vegetables.

On a macro level it includes replacing traditional concrete with permeable concrete that allows water to pass into the ground while also incorporating large parks, urban forests and constructed wetlands into the very design of a city. These spaces not only act as natural flood storages but also help filter water of impurities (in conjunction with wastewater filtration systems) and can be used to replenish groundwater aquifers – something of critical importance in an increasingly thirsty world and especially in countries like the UAE and Saudi Arabia. And they make cities look good while doing it.

In professor Yu’s native China, while there was initial skepticism over the feasibility of such sweeping redesign, the 2012 Beijing floods ended such arguments and now the program has been adopted in over 250 cities with Shenzen being a prime example of the model’s success and aesthetic appeal. Nothing succeeds like success and the model is now also being adopted in Russia, Indonesia and the United States, with concrete jungles turning into, well, actual jungles.

Given that large amounts of urban spaces are filled with rooftops, sponge cities incorporate ‘blue-green’ roofs covered in vegetation (mosses grasses and ferns) rooted in soil over a permeable rock layer which then not only absorbs and stores water, but also helps keep the building cooler that its less-green counterparts.

Sponge cities, then, also have the added benefit of keeping ambient temperatures down in a world that’s getting wetter and hotter; Pakistan this year saw not only its wettest April in 60 years but is also currently experiencing one of its hottest summers to date and while sweeping redesign may not be possible, one must at least start small and begin implementing at least some of these models and techniques to ensure that our towns and cities do not become unliveable.

The costs of implementing such projects can be huge, but they are dwarfed by the clear costs of inaction.

- Zarrar Khuhro is a Pakistani journalist who has worked extensively in both the print and electronic media industry. He is currently hosting a talk show on Dawn News. Twitter: @ZarrarKhuhro