Millions At Risk As Almost Half Of All Major Chinese Cities Are Sinking, Warns Study

Nearly half of China's major cities are skinking because of water extraction and due to the increasing weight of urban buildings and infrastructure, a new study has found. The research, published in the journal Science, discovered that Chinese cities, including Beijing and Tianjin, are facing a "moderate to severe" risk of subsidence. 45% of China's urban land was sinking faster than 3 millimetres per year, with 16% at a rate of over 10 millimetres per year, the study revealed. 

For the research, scientists measured land subsidence in every Chinese city with a population of more than 2 million people over the period from 2015 to 2022. Of the 82 cities they examined, the team found that some cities are subsiding rapidly, with one in six exceeding 10mm per year. They also found that while China's biggest city Shanghai continues to subside after sinking up to 3 meters over the past century, Beijing is sinking 45 millimetres annually near its subways and highways. 

"The subsidence appears to be associated with a range of factors such as groundwater withdrawal and the weight of buildings," the researchers wrote in the study, as per Live Science. "High-rise buildings are sprouting up, road systems are expanding, and groundwater is being used, all at a rapid pace," they explained.

"In addition to the national pattern of city subsidence, we identified several natural and human factors that were associated with city subsidence," the team wrote in the study. The natural factors include the geological setting of each city and the depth of the bedrock, which influenced the amount of weight the ground could hold up without sinking. The scientists also found a strong link between sinking cities and groundwater loss, which leaves empty pore space in the crust that becomes compacted as weight piles on above. 

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Other factors, according to research, include urban transportation networks, as well as hydrocarbon extraction and mining. But "the key to addressing China's city subsidence could lie in the long-term, sustained control of groundwater extraction," the researchers emphasised.

"Subsidence jeopardizes the structural integrity of buildings and critical infrastructure and exacerbates the impacts of climate change in terms of flooding, particularly in coastal cities where it reinforces sea-level rise," Robert Nicholls, a professor of climate adaptation at the University of East Anglia in the UK said in a statement.

Researchers cautioned that the new findings reinforce the need for a national response even in other susceptible cities outside China.