Research Results, Almost Half of China's Big Cities "Sunk"

About 16 percent of them sink more than 10 mm per year. The causative factors are the decline in groundwater levels and the large burden of buildings in urban areas.

“With China's urban population already exceeding 900 million people, even the slightest land subsidence in China could pose a major threat to urban life,” said a research team led by Ao Zurui from South China Normal University in Guangzhou.

The decline in land surface has resulted in an annual loss of more than 7.5 billion yuan in China. In the next century, almost a quarter of China's coastal land is expected to fall below sea level. As a result, hundreds of millions of people in the region are threatened by flooding.

"This finding truly highlights that for China, land subsidence is a national issue, not just a problem in one or two places. And, this is a microcosm of what is happening all over the world," said Robert Nicholls of the Tyndall Centre for Climate Change Research, University of East Anglia, UK.

Also read: Floods still inundate the city of Zhengzhou in China, the streets are a mess

One of the cities worst affected by land subsidence is Tianjin in northern China. Quoted from China's official news agency, Xinhua, in 2023, as many as 66,000 people were evacuated from the port city of 15 million people due to floods.

In the same year, 3,899 residents were evacuated from 25 apartment buildings and other high-rise buildings in the city after a landslide occurred. The incident caused roads to crack and split.

With an urban population in China that has exceeded 900 million people, even a small decrease in land can be a significant threat to urban life.

Geology experts suspect that the collapse of the soil is caused by underground cavities at a depth of 1,300 meters. Investigation results found that the incident was caused by a decrease in groundwater and the development of geothermal wells.

Furthermore, several districts in China have also experienced excessive coal mining, causing cavities underground. Authorities often have to inject concrete into collapsed holes in those districts to strengthen the soil structure.

This problem is not only happening in China. Another study published in February 2024 stated that around 6.3 million square kilometers of land worldwide are at risk of land degradation. According to a 2022 study in Singapore, out of 44 major coastal cities experiencing land subsidence, 30 of them are located in Asia.

One of the countries with a high risk is Indonesia. Currently, most of the capital city of Jakarta is located below sea level.

Also read: Land subsidence along northern Java is increasingly worrying

Nicholls stated that vulnerable cities can learn from Tokyo. The capital of Japan sank 5 meters in the 1970s. To prevent it from getting worse, the Japanese government at that time banned the use of groundwater.

"The mitigation of land subsidence must be taken very seriously. However, not everything can be stopped, so adaptation and embankment construction are needed," he said.

Matt Wei, a geophysics expert from the University of Rhode Island, US, said that this issue stems from urbanization and population growth. "This is an issue of urbanization and population growth. Greater population density, more water extraction, and land surface reduction," he said. (REUTERS)