China’s major cities are facing a double threat from human activity and rising sea levels. New research published in the journal Science reveals that land subsidence, the sinking of land, impacts millions of people across the country. Nearly half of China’s urban areas, home to 270 million residents (29% of the population), are subsiding at a rate exceeding 3 millimeters (0.12 inches) annually. This translates to a significant portion of the population living on the ground steadily sinking beneath their feet.

The study identifies excessive groundwater extraction as a primary culprit. Cities across China have been pumping water from underground aquifers at an unsustainable rate, exceeding the natural pace of replenishment. This issue is further exacerbated by climate change-induced droughts, putting even more significant strain on these vital water sources. As the water table lowers, the overlying land loses support, causing subsidence.

The weight of burgeoning cities themselves also plays a role in land subsidence. Soil naturally compacts over time under the increasing weight of accumulating sediments. Additionally, the construction of heavy buildings exerts further pressure on the ground, contributing to the gradual sinking of the land.

While land subsidence is not unique to China, the research highlights the nation’s particular vulnerability. Dozens of coastal cities worldwide, including New York City in the United States and Mexico City, are experiencing similar problems. However, the situation in China is compounded by many of these sinking areas being also coastal regions.

The impact of subsidence is particularly devastating in coastal zones, where rising sea levels pose an additional threat. The combination of these two factors exposes vast swathes of land and the people and property situated there to increased risks of flooding. The study suggests that roughly a quarter of China’s coastlines could end below sea level due to subsidence and projected sea level rise. This scenario presents a significant risk to life and property in major cities like Tianjin, Shanghai and Guangzhou.

However, the research also acknowledges ongoing efforts to mitigate these risks. Some coastal areas, like Shanghai, have already implemented impressive dike systems that stand several meters tall. These structures protect against flooding, even in the face of land subsidence and rising sea levels. Experts note that such large-scale coastal defenses are yet to be commonplace in other countries, highlighting China’s proactive approach in certain areas.

The Chinese government has taken steps to address the issue, including implementing stricter regulations on groundwater pumping in recent years. These measures have demonstrably slowed the subsidence rate in Shanghai and surrounding areas. Additionally, China’s ambitious water diversion project, which transfers water from the Yangtze River in the south to water-scarce regions in the north, has helped to alleviate pressure on groundwater resources and halt subsidence in Beijing.

The researchers suggest that continued control of groundwater extraction in significant cities and ongoing maintenance of coastal dike systems are crucial for long-term success. By acknowledging the challenges of land subsidence and implementing effective mitigation strategies, China can safeguard its population and infrastructure from the growing risks associated with a sinking landscape and rising sea levels.