The ground beneath many Chinese cities is steadily sinking. Researchers are now warning that the risk of flooding is increasing in the country’s coastal metropolises. In the next hundred years, a quarter of the area could even sink below sea level.
Land subsidence may have long-term consequences, especially in densely populated coastal areas, researchers warn in the journal ‘Science’. This means a significant flood risk for large population groups. There would also be direct damage to buildings and foundations, infrastructure and sewers.
The megacity Beijing is also hit hard by land subsidence. In Shanghai, parts of the city are known to have sunk up to three meters over the past century. The research team led by Zurui Ao from South China Normal University in Foshan now evaluated satellite measurements of 82 major Chinese cities covering 74 percent of the country’s urban population between 2015 and 2022. About a third (29 percent) of the population in these cities suffer from subsidence of more than three millimeters. According to the researchers, a total of 920 million people lived in urban areas in China in 2020; an estimated 270 million of them lived on sinking land.
Buildings have a considerable weight
Land subsidence is associated with a number of factors, including groundwater extraction and the weight of buildings. In recent decades, China has experienced one of the fastest and most extensive urban expansions in human history, the researchers said. Cases of land subsidence are already being reported more and more often in large cities. Subsidence-related disasters in China have caused hundreds of deaths and injuries in recent decades, as well as enormous economic damage.
“The results emphasize the need to strengthen protective measures and strictly control groundwater extraction,” the study said. Long-term controls and more sustainable water management, such as those already successfully implemented in the Japanese cities of Tokyo and Osaka, could also help stabilize the rate of land subsidence in China.
Subsidence is often caused by people
Land subsidence is a phenomenon that causes major problems not only in China but also in many other parts of the world. It is often caused by human activities such as overexploitation of groundwater, intensive development or oil and gas extraction. But natural geological factors also play a role. For example, cities like Venice, Italy and Mexico City, Mexico are known for their land subsidence problems.
In some parts of the world there are opposing processes – for example due to the continued rise of land areas freed from the weight of the ice sheet of the last ice age.
Source: Krone
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