Half of China's major cities sinking: A crisis affecting millions

China is grappling with a severe issue. Over half of its major cities are threatened by land subsidence, a problem that could impact more than 100 million people within the next century. Scientists are raising alarms about the potential consequences.

Research conducted by scientists from the University of East Anglia and Virginia Tech highlights the dangers nearly half of China's 82 largest cities face due to rapid land subsidence. According to their findings in "Science," this troubling trend could affect between 55 and 128 million individuals by 2120 unless proactive steps are taken.

Despite its significant threat, the issue of land subsidence in Chinese cities has been largely ignored and underestimated. The researchers point out that land subsidence is a widespread process that can have dramatic outcomes. Up to 19% of the global population could be at risk from this phenomenon.

The primary culprits of subsidence include both natural and human-induced factors, with the extraction of groundwater for human use playing a key role.

To gauge the extent of the problem, the team analyzed satellite data on land subsidence across China, focusing on 82 cities where nearly 700 million people reside. Their analysis revealed that 45% of these urban areas are sinking, impacting 270 million residents. Moreover, in 16% of these areas, the land is subsiding at a rate of 0.4 inches per year or more, affecting approximately 70 million people, with Beijing and Tianjin facing the most severe situations.

Coastal cities, like Tianjin, are especially prone to the dangers of subsidence, compounded by rising sea levels due to climate change. This combination of factors has already shown devastating effects, such as in New Orleans during Hurricane Katrina in 2005, which led to significant flooding and was one of the biggest natural disasters in the history of the United States.

In Beijing, the vibrations caused by traffic and tunnel digging are accelerating land subsidence. Areas near subway lines and highways are experiencing sinking rates of about 1.8 inches per year. Shanghai, China's largest city, has also seen a dramatic reduction in ground level—by about 10 feet over the last century—with the trend showing no signs of slowing.

Experts warn that if the current pace of land subsidence and sea-level rise continues, the area of Chinese cities below sea level could triple by 2120, posing a threat to between 55 and 128 million people. Without urgent action from the authorities, the results could be disastrous.

“Land subsidence endangers buildings and critical infrastructure and amplifies the impacts of climate change, like flooding, especially in coastal areas vulnerable to sea-level rise,” says Professor Robert Nicholls from the University of East Anglia.

There is hope, however, as seen in Osaka and Tokyo. Changes in groundwater use policies in the 1970s led to a significant reduction or halt in subsidence. The researchers argue that addressing land subsidence goes beyond just Chinese cities and is a global concern that requires a concerted effort from the scientific community and urban planners to find and implement solutions.