Sinking cities: how China is moving subsidence research forward

Faced with the double threat of rising sea levels and subsiding ground, researchers are devising plans to bring communities back from the brink.

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In China, the main cause of subsidence linked to human activity is the excessive extraction of groundwater as cities expand, says Zhang Yonghong, a researcher at the Chinese Academy of Surveying and Mapping in Beijing. The practice lowers the underground water level, which causes the surrounding soil to compact and the land to sink. “The building of infrastructure, such as subways, can also cause parts of a city to subside,” Zhang says.

Disruption to the natural recharging of groundwater owing to paved urban surfaces can worsen the situation, says Yu Kongjian, a landscape architect at Peking University in Beijing. “Land subsidence is one of the most profound manifestations of ecological mismanagement in urban regions,” he says.

Cities are also getting heavier as they grow, says Zhao Qing, a geodesist at East China Normal University in Shanghai. Ongoing research by her team suggests that the increasing weight of buildings is one of the three factors — together with dropping groundwater levels and the nature of the soil — that are causing Shanghai and other cities in the Yangtze River Delta region to subside.

None of the above is unique to China, and some of these issues — such as groundwater extraction and building weight — often affect cities inland, too. But on the coast, these factors are driving the land downwards in areas that also face accelerated sea-level rise owing to climate change.

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