Sponge cities: the Chinese proposal to adapt to climate change

Before being an architect, Yu Kongjian was a farmer.

During his childhood, each year he eagerly awaited the arrival of the monsoon in his village in the eastern Chinese province of Zhejiang: the floodwaters of the rivers fertilized the fields and filled the ponds with fish for food and for sale.

The young Yu was observing the techniques of his relatives and neighbors to extract the maximum yield from those rains.

Now, this 59-year-old architect is inspired by these agricultural traditions for his proposal for

against floods and as a way of adapting to climate change.

A proposal that is applied in more than 30 Chinese cities and that has already been exported to another dozen countries.

Floods and droughts have always existed.

But climate change has increased its dimensions and its frequency.

Only last year deadly floods of water were registered in the United States, Germany, India or China, where the authorities spoke of the "worst rains in a millennium".

Global losses from flooding reached 76 billion dollars (67 billion euros) worldwide in 2020. More than 2 billion people live under the threat of drought.

And given that these phenomena are increasing, the need to find solutions is urgent.

Until now, conventional responses to heavy rains, imported from the West, have involved channeling water through

: pipelines, concrete lined roads, dams, dikes.

With them "you fight against water, instead of adapting to it," says Professor Yu, trained at Harvard and founder of the School of Architecture and Landscaping at Peking University, the most prestigious in China.

“Those rigid channels cannot absorb excess water.

Instead, they overflow in an uncontrolled way and accelerate the speed with which the current travels, which becomes dangerous.

It's like the system of the body's veins: they have to be flexible to better transport the liquid they contain”, he adds in a telephone conversation with this newspaper.

Only 20% of rainwater in densely built cities seeps into the ground.

Instead, Yu's bet proposes versatile cities that absorb water instead of rejecting it, that accumulate it and can recycle it in dry seasons or for uses such as irrigation.

Instead of straight canals and concrete walls, he seeks to reclaim and widen natural riverbeds—the Yangtze and its major tributaries alone have lost 333 tributaries to urbanization.

The idea is that natural meanders help slow down the flow of water, which can then be more easily controlled.

Its banks are planted with vegetation, which helps to absorb and clean the waters.

The

of this architect are also endowed with numerous parks and ponds, which can retain water in times of intense rain.

The architect Yu Kongjian, in a photo provided by his studio WanQuan

Asphalt is replaced by permeable materials, capable of letting water seep into the subsoil and removing it from the surface in a matter of hours.

Buildings, in his vision, can absorb water on vegetated roofs, vertical gardens or on permeable walls.

“Water is productive, it is a treasure, the sustenance of life.

Protect biodiversity.

With it we can produce food and biomass”, he recalls.

He maintains that his proposal is not a simple formula, but a whole “philosophy”: “based on nature”.

"It's the art of survival," Yu explains.

“How we adapt to climate change”.

According to him,

“are not only a solution to the problem of floods, but also to urban droughts.

They help to manage water better, to increase water resources, to clean water.”

A particularly serious problem in China, where —recalls Yu— 70% of surface water resources are contaminated.

Although Yu already defended this model from the architecture studio he founded in 1998, Turenscape, his moment came in 2012. That summer, Beijing suffered its biggest floods in decades, which claimed a dozen lives and damages valued at 2,000 million dollars. .

Four months later, Chinese President Xi Jinping came to power, who has made the fight against pollution and climate change one of his main mottos.

In 2013, the Chinese government adopted the development of an “ecological civilization”, which included

, in its national program .

Between 2015 and 2016, around thirty cities launched the first pilot projects, including the coastal Shanghai or Qingdao, with perpetual water management problems.

With a minimum area of ​​five square miles per project, the goal was for at least 70% of rainwater to be recovered by 2020 in each of them.

Today, more than 40,000 of these projects have been undertaken in different cities in China, according to data from the country's Ministry of Housing.

Professor Yu's studio, which employs some 600 people in three offices, has personally handled almost 600 projects in 200 cities.

The government goal is that by 2030, the year in which China has pledged to have reached its emissions peak, cities with more than one million inhabitants capture 80% of their rainwater.

His ideas have inspired other cities, from Britain's Slough to Russia's Kazan, as well as Mexico City, which suffers from water management problems similar to those of Chinese megalopolises.

Yu's ideas connect with other similar movements in different areas of the world, from

European

in Canada.

The Chinese professor assures that his philosophy has the advantage of taking advantage of the techniques that Chinese agriculture used for centuries.

“2,000 years ago, Chinese farmers already knew that if you cultivate four hectares of land, you have to leave one hectare of land to water,” Yu cites as an example.

“The

is a solution that is based on and inspired by the wisdom of the Chinese agricultural civilization, a kind of wisdom that has been forgotten for decades because we follow the western model of city building, and forget our tradition of adapting to the nature," he insists.

As he points out, his ideas can be applied in any city in the world: the key is to adapt to the circumstances and terrain of each place.

"It can be done very cheaply," he says, "what we use is already there, in nature."

According to him, existing cities can be adjusted to create sponges.

“There is always margin.

You can create ditches in the gutters, gardens on the roofs of buildings, put ditches, ponds in patios...”.

This, among other things, increases the city's capacity to absorb water and reduces the impact of rain on the drainage system and other public infrastructure.

But not everyone is so optimistic.

Other architects consider that, in themselves,

are not enough to mitigate the effects of torrential rains.

The floods in the city of Zhengzhou, in Henan, in the summer of 2021 left nearly 400 dead, despite the

projects adopted.

“It is an excellent sustainable perspective for a certain type of water management, but it remains debatable whether it can be considered a complete solution to flood risk management in such a context of climate change” as the one that affected Zhengzhou at the time, says the architect Chen Long, adjunct professor at Peking University of Technology, speaking to Chinese state television CCTV.

But proponents of the proposal, led by Yu, insist that it is.

When failures occur, they say, it is either because not enough space has been devoted to creating this sponge effect - the minimum size of 5 square kilometers is small in a metropolis whose total area can be 500 times larger - or because the projects have not been undertaken in the right place or in the right way: houses should not be built, for example, in natural areas where streams drain.

"In the case of Zhengzhou, it was not a true

An official investigation indicated that 20% of the funds available for

projects were used in other projects that had nothing to do with it!", qualifies this architect.

concept

is not limited to urban planning, and individual citizens can also implement it in their communities and homes.

Yu himself applies it to his own, where he has installed porous walls on the outside that allow plants to grow and on the roof of which collects rainwater that, filtering, waters them.

“I collect 50 water tanks and I have managed to harvest 32 kilos of vegetables”, he proudly boasts.

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