BEIJING: Nearly half of China’s major cities are experiencing sinking or subsidence problems at the “moderate to severe” stage, according to a study of national satellite data released on Friday (April 19).
He added that this problem puts millions of people at risk of flooding, especially when sea levels rise.
The authors of the paper, published by the journal Science, found that 45 percent of China’s urban land is sinking at a rate of more than 3 mm per year, and 16 percent is experiencing subsidence of more than 10 mm per year. weight of the built environment.
With China’s urban population already exceeding 900 million people, “even a small portion of China’s land subsidence could pose a major threat to urban life,” said a research team led by Ao Zurui of South China Normal University.
Land subsidence has caused annual losses of more than 7.5 billion yuan (US$1.04 billion) in China, and in the next century, nearly a quarter of coastal land could be lower than sea level, putting hundreds of millions of people at risk. bigger inundation.
“This really brings home that for China this is a national problem and not a problem in just one or two places,” said Robert Nicholls of the Tyndall Center for Climate Change Research at the University of East Anglia. “And this is a microcosm of what’s happening around the world.”
The northern city of Tianjin, home to more than 15 million people, was identified as one of the worst affected. Last year, 3,000 residents were evacuated after a “sudden geological disaster” that investigators said was caused by a lack of water and the construction of geothermal wells.
Many of China’s old coal districts also suffer from excessive mining, and authorities are often forced to inject concrete into collapsed pits to strengthen the soil.
The problem is not unique to China. A separate study published in February said about 6.3 million square km of land worldwide was threatened. One of the countries most affected is Indonesia, with most of the capital Jakarta now below sea level.
Nicholls said vulnerable cities could learn lessons from Tokyo, which sank about 5 meters until the country banned groundwater extraction in the 1970s.
“Mitigating land subsidence has to be taken very seriously, but you can’t stop everything so what you’re talking about is adaptation and building embankments,” he added.
Of the 44 large coastal cities experiencing this problem, 30 are in Asia, according to a study in Singapore in 2022.
“This is a problem of urbanization and population growth – greater population density, more water withdrawals, (and) more drowning events,” said Matt Wei, a geophysicist at the University of Rhode Island.
