270 million people sinking in China’s cities

Dozens of Chinese scientists have raised a red flag using a detailed satellite data analysis to plot land movement across China, writing that a third of the country’s urban residents could find themselves living in a ‘sinking city’.

Led by Zurui Ao, Xiaomei Hu and Xie Hu from South China Normal University and Peking University, the research published in the journal Science found that nearly half of urban areas studied had subsided more than 3mm each year from 2015-2022. A sixth are receding at more than 10mm annually.

This, they say, is occurring for several reasons, including natural geology, human-related factors such as groundwater removal – which was found to have a “widespread” influence on subsiding cities – and building weight.

While these factors were consistently seen across the 82 cities investigated,  other prominent factors included transportation systems in larger cities, as well as regions where land reclamation has taken place, and mining sites.

In all, some 270m people may find themselves living in urban areas, including  67m in areas that are sinking a centimetre every year. Larger cities like Beijing and Tianjin have the greatest populations experiencing subsidence.

In a double-whammy, coastal cities experiencing subsidence may also be at increasing threat of sea level rise,  due to global warming.

The research has been praised by climate researchers Robert Nicholls, director of the UK-based Tyndall Centre for Climate Change Research, and Manoochehr Zhirzaei a geophysicist at Virginia Tech.

“Subsidence jeopardises 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,” says Nicholls, who was not involved in the study, but researches adaptation and resilience measures in costal regions.

“Many cities and areas worldwide are developing strategies for managing the risks of climate change and sea-level rise. We need to learn from this experience to also address the threat of subsidence which is more common than currently recognised.”

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