The construction of Xiang’an international airport, in Xiamen – Reuters
A giant with feet of clay? Certainly, a giant that is “sinking”. Slowly. But inexorably. The alarm comes from a study published by the magazine Science and relaunched by Reuters: Nearly half of China’s major cities suffer from levels of subsidence considered “moderate to severe.” Translated: the ground on which the Asian giant’s metropolises rest is sinking at a rate of more than 3 millimeters per year. For 16% the speed is greater than 10 millimeters per year. An erosion considered “irreversible”.
According to the team of researchers led by Ao Zurui of South China Normal University, who carried out the research, the phenomenon exposes millions of people to the risk of flooding, because it is combined with another dramatic “climate” change: the rise in sea levels . Not only. According to the journal Nature, “subsidence is a global geological environmental problem that threatens the human living environment.”
But what are the causes of this lowering of the ground? Scholars speak of the combined effect of two factors: the drying up of aquifers but also the burden created by the human environment (constructions and buildings). According to Robert Nicholls of the Tyndall Center for Climate Change Research, this is not a localized or partial risk.
But of “a national emergency”. One figure captures the enormity of the risk: China’s population concentrated in cities amounts to 900 million people. The most vulnerable city? The northern metropolis of Tianjin, which is home to more than 15 million people and “boasts” an urbanization rate of over 80%. According to the photograph taken by the College of Urban and Environmental Sciences, land subsidence in Tianjin was first reported in the 1920s “while rapid subsidence (several centimeters per year) began to occur in the 1960s”: what is classified as “a serious failure” has been underway for over half a century.
According to Reuters, “subsidence” already costs China more than 7.5 billion yuan ($1.04 billion) in annual losses, and by the next century, “nearly a quarter of coastal lands could actually be below sea level, placing hundreds of millions of people at even greater risk of flooding.” . The problem does not affect China alone. A separate study published in February says about 6.3 million square kilometers of land worldwide are considered at risk. Among the most affected countries is Indonesia, with much of the capital Jakarta already now below sea level. According to another research, published in 2022, of the 44 main coastal cities exposed to risk, thirty are concentrated in Asia. “It’s a problem of urbanization and population growth: higher population density, more water extracted and more subsidence,” Matt Wei, a geophysics expert at the University of Rhode Island, told Reuters.
