Romain Rouillard / Photo credit: CFOTO / NURPHOTO / NURPHOTO VIA AFP
What if China began to pay a high price for its policy of rapid urbanization. According to a study published by the journal Science and spotted by Franceinfo, 45% of the country’s 82 large cities are sinking into the ground by at least 3 mm per year. A figure which even reaches 1 cm per year in 13 of them, including Beijing. To reach this conclusion, the researchers adopted a satellite observation technique, carried out between 2015 and 2022. In total, around 270 million Chinese are affected.
Overexploitation of coal
According to the study, this phenomenon is directly linked to the rapid development of road infrastructure, the unbridled construction of new buildings and the sustained use of groundwater which lowers the level of water tables and weakens the soil. “In China, many people live in areas that have been sedimented quite recently, geologically speaking. So when you remove groundwater or drain soils, they tend to subside,” explains the Professor Ribert Nicholls, director of the Tyndall Center for Climate Change Research, quoted by the BBC. Finally, this risk can also be attributed to the overexploitation of coal, more particularly in the Pingdingshan region, where the land is sinking into the ground by approximately 1.09 cm per year.
A process far from risk-free. “Subsidence leads to cracks in the ground, damages buildings and civil infrastructure and increases the risk of flooding,” the study points out. The cost of losses directly linked to this phenomenon has already reached more than 7.5 billion yuan. Hong Kong media HK01 takes the example of the city of Tianjin, in the North, where 3,000 people had to be evacuated last June due to a crack in the ground and large-scale subsidence.
Acceleration of the risk of marine submersion
Above all, this subsidence of buildings raises fears of the worst in coastal towns, already faced with rising sea levels linked to global warming. And could thus accelerate the risk of marine submersion which already threatens many cities. According to the study, a quarter of these megacities will, within a century in China, be below sea level. This will make the floods currently experiencing the country even more devastating. Elsewhere in the world, many megacities are having to face a phenomenon of subsidence. This is the case for New York, Jakarta in Indonesia, Manila in the Philippines and Auckland in New Zealand.
Aware of the problem, China has already taken the lead and adopted a series of measures intended to curb part of the phenomenon. In particular the increased control of the extraction of groundwater, as in Shanghai where the study notes a slower level of subsidence than in the rest of the country. A solution which has also proven convincing in Tokyo and Osaka, in Japan, victims of a similar phenomenon.