A comprehensive new analysis by Chinese scientists reveals that major cities across China are experiencing sinking, posing a significant threat to a substantial portion of the country’s rapidly urbanizing population in the upcoming decades.

The phenomenon, known as subsidence, occurs when land sinks relative to its surroundings, presenting a considerable challenge for urban areas worldwide. It exacerbates the local sea level rise induced by climate change, as the land sinks while the ocean levels rise. Urban subsidence can also impact inland cities by causing structural damage to buildings and roads, as well as creating drainage issues when water becomes trapped in sinking areas.

The study, published in the journal Science and conducted by over 50 scientists at Chinese research institutes, surveyed 82 major Chinese cities. Alarmingly, nearly half of these cities are experiencing measurable subsidence. The affected regions are home to nearly one third of China’s urban population. The researchers estimate that approximately a quarter of China’s coastal land will be submerged below sea level within the next century, primarily due to subsidence.

This poses an immediate risk to tens of millions of people, a number that could escalate to hundreds of millions if China’s urban centers continue to expand in population and experience subsidence at current rates, while sea levels continue to rise steadily due to greenhouse gas emissions.

Robert Nicholls, a subsidence expert at the University of East Anglia in England, emphasizes the magnitude of the problem, stating, “This is a big problem…This is not a local problem, but a national, or even international, problem.”

This study marks the first time that scientists have utilized satellite data to systematically quantify the extent of sinking in Chinese cities. The analysis covered the period between 2015 and 2022. While recent studies in Europe and the United States have also identified significant subsidence in certain cities, they have not observed the widespread sinking observed across China.

Nicholls notes that Asia faces higher risks due to the geological factors present in many Asian cities, particularly those built on river deltas prone to sinking when subjected to the weight of heavy buildings and excessive groundwater extraction.

Understanding the extent and causes of urban sinking is crucial for urban planners and policymakers to implement measures to prevent future subsidence and potentially reverse existing sinking. Strategies such as banning further groundwater extraction in rapidly sinking areas and replenishing groundwater levels through managed aquifer recharge can mitigate subsidence effects.

For instance, Tokyo successfully stabilized the lowest parts of the city, which subsided by as much as 15 feet in the twentieth century, by enforcing stringent groundwater regulations.

Moreover, detailed studies focusing on individual cities are necessary to identify the most affected areas and develop tailored solutions to address subsidence challenges and mitigate future risks.