Advertisement

What are China's 'sponge cities' and are they working?

STORY: China's so-called "sponge cities" were designed to boost flood resilience in metropolitan areas.

But their effectiveness is now under scrutiny, after devastating floods inundated cities there in recent weeks.

The extreme weather has caused deaths, destroyed homes, and damaged infrastructure.

So what is the "sponge city" scheme, and why hasn't it worked?

China has long sought to improve the way it handles extreme weather.

Breakneck urbanization has left vast stretches of land in impermeable concrete, often along banks of major rivers that traditionally served as flood plains.

With wetlands paved over and nowhere for surplus water to settle, waterlogging and flooding is commonplace.

"Sponge cities" were designed to make greater use of lower-impact, "nature-based solutions".

Essentially, ways to better distribute water and improve drainage and storage.

"Sponge city" plans include the use of permeable asphalt, building new canals and ponds, and restoring wetlands.

The goal is to ease waterlogging and improve the overall urban environment.

And for China, the need to find a solution was ramping up.

2018 data showed 641 out of 654 large- and medium-sized cities were vulnerable to floods and waterlogging.

So what has been done so far?

Studies show that many of the local pilot initiatives have had a positive effect.

But implementation has been patchy.

Just 30 pilot sponge cities were selected in 2015 and 2016.

And by last year, only 64 of China's 654 cities had produced legislation to implement sponge city guidelines, researchers said back in January, adding that the government had so far paid "minimum attention" to sponge city construction.

They called for national legislation to be drawn up as soon as possible.

"Sponge cities" do have some limitations.

And even if measures had been fully implemented, they wouldn't have been able to prevent this year's disasters.

Experts believe sponge city infrastructure can only handle 7.9 inches of rain per day.

Zhengzhou in Henan province, for example, was one of the most enthusiastic pioneers of sponge city construction.

It allocated more than $8 billion to the program from 2016 to 2021.

But in July 2021, it saw rainfall of almost 8 inches in one hour.

Authorities are also playing catch-up on climate change.

This year's heavy rain hit cities in the normally arid north, where sponge city development is less advanced.

Officials warn China is especially vulnerable to the impacts of global warming, due to its large population and unevenly distributed water supplies.