China's 'Sponge Cities’ That Absorb Rainwater Pushed Past Limits

Nearly a year's worth of rain fell on the Chinese city of Zhengzhou over four days this month. Flooding killed 71 people, including 14 trapped in a subway station as waters rose.

Zhengzhou is part of a Chinese government initiative to build "sponge cities" in response to increasing urban flooding across the country. These cities aim to use natural processes to soak up rainwater rather than sending it coursing through concrete drainage pipes and channels that can get overwhelmed or cause other problems. These systems are catching on around the world as city planners embrace the benefits they provide, such as stormwater management, urban cooling and aesthetic appeal. But experts say the storm that drowned Zhengzhou was more than any city's drainage system could handle. And because of climate change, these kinds of storms are becoming increasingly common around the world.