It’s raining again in China.
None of us like the rain, but here it’s gone from mild annoyance to a serious problem.
Once a largely rural country, China now has more than 100 cities with populations of over
a million people - and all that building on former farmland has led to a major downside - flooding
But instead of constructing big barriers like others have done, China is turning back to
nature for the solution, upgrading its cities so that they welcome the water
rather than hold it back.
Get yourself comfortable and prepare to soak-up China’s sponge cities.
China is home to more large cities than any other nation.
60% of its 1.4BN citizens now reside in urban areas and creating the space for them to live,
work and play has meant replacing huge areas of green space with sprawling buildings and infrastructure.
That’s a lot of land that would previously have absorbed rainwater being replaced with
surfaces that do the opposite - and all in a country that regularly experiences heavy storms.
Little surprise then that flooding has become such a serious problem -
even in places with good drainage.
In 2020, over just two months, more than 400 rivers flooded across China - many of them
worse than ever before - and at least 50 million people were impacted.
On top of that, water shortages are occurring in some cities where water runs off the streets
too quickly to enter water systems that are already overstretched.
The response from China’s government was to mop up this mess and convert many of these areas
into so-called sponge cities.
This is where areas are redesigned to cope with and process rainwater in a few different
ways - soaking it up, storing it and releasing it when needed, a bit like - you guessed it
- a sponge.
Now, this usually involves combining what’s known as grey and green infrastructure – so
things like advanced drainage and water treatment systems alongside natural and semi-natural areas.
The US, Russia and India have all dabbled in sponge cities, but China’s programme is on
an entirely different scale.
Brace yourself for quite a few numbers.
16 cities were chosen to be part of the scheme when it launched in 2015 and
another 14 joined a year later.
The aim is to have 80% of these 30 cities absorbing and reusing 70% of rainwater by 2030.
Hopefully you followed all that.
That means massive changes to land use, surfaces, underground infrastructure and more across
the world’s most populated country.
Although it sounds like a lot of work that needs to be done in not much time, this is
China we’re talking about, so of course they’ve already made huge progress.
Chongqing, which has a population of over 16 million, can now rather grandly call itself
one of China’s leading sponge cities.
Here, a new park in the Tongnan District helped the area recover quickly from the worst storm
for 100 years in 2020.
Until 2019 just a small concrete barrier separated the Fu River from land that was becoming
increasingly vulnerable to flooding.
Now, the barrier is gone and when levels rise, water is free to flow into this incredible
maze of constructed wetlands.
Built over 99 hectares, it’s an impressive network of native plants, trees, ponds, islands
and elevated walkways, making it more than somewhere for excess water to go - people
want to be there too, “soaking-up” their surroundings.
Chongqing was also the first sponge city to be given a smart digital control system which
lets authorities monitor its sewer and stormwater networks in real time.
With this, they can control how water flows into the natural environment more precisely,
analyse how well the whole system performs in extreme weather and
use the data to prevent future floods.
To the east of the country, on the banks of the Yangtze River,
Zhenjiang has also gone big with sponges.
As well as rain gardens and creeks that drain and retain rainwater, the city has been equipped
with a system of bioswales, which stretch for several kilometres in total.
These specially engineered channels with sloped sides funnel stormwater inside, where it filters
slowly into the ground beneath - often with debris and pollutants removed as part of the process.
Go for a stroll in any decent sponge city and you’ll also find permeable roads, paths
and cycleways - all of which allow water to soak directly into the material instead of
forcing it into drainage systems that can become quickly overwhelmed.
Polyurethane binders are combined with gravel or stones to create a surface with similar
properties to concrete or tar, but with tiny cavities that let water through.
Around 4,000 litres of water per square metre can be absorbed each hour, and there are now
networks of these across China, from Qian’an City to Hangzhou, which is set to host the
2022 Asian Games.
Now that event is actually relevant to this video because this site for the tournament was
designed as one big sponge city project - a fantastic place to soak-up the sporting atmosphere.
Previously a flat piece of land, the area is being transformed into a 116-acre eco-park
spread across a rolling hillscape.
Rainwater will be collected, filtered and reused for water features, plumbing, heating
and cooling - according to Archi-Tectonics, which designed the masterplan.
But despite all of this work, China’s sponge cities haven’t been able to prevent every
flood from occurring, including one notable recent example.
In July 2021, the city of Zhengzhou had almost a year’s worth of rainfall in just four
days, leading to extreme flooding that tragically killed hundreds of people.
Zhengzhou had spent over $7BN upgrading hundreds of flood-prone areas, as well as the drainage system.
Unfortunately these improvements were completely overpowered, leading many to criticise the
city’s efforts and question the effectiveness of the entire programme.
But Chinese officials responded by pointing out the severity of the storm, claiming that
no city would’ve been able to avoid taking heavy flood damage in such a situation.
Experts also say that sponge city projects are only really meant to protect against light
to moderate storms and floods, which kind of brings us on to the main point.
Schemes like these do their job in most scenarios, there are lots of different options to suit
a variety of cities and they look great too.
But, with severe events like the one in Zhengzhou expected to become more common, we’ll need
more than this to stop further tragedies from occurring.
Even with that said, for most cities worried about water levels, introducing a sponge strategy
of their own, or something similar, is likely to put them on a much firmer footing in the future.
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