The main cause of the problem is excessive use of water resources.
According to a recent study, nearly half of China’s big cities are sinking, the main cause of the problem being excessive water extraction, reports the BBC. The subsidence of some settlements is taking place at an extremely fast pace, the subsidence of every sixth city exceeds 10 millimeters per year.
China has experienced explosive urbanization in recent decades, and large amounts of water are being extracted in urban areas. In coastal cities, the situation is aggravated by sea level rise caused by climate change.
The problem of land subsidence was already noticed in Shanghai in the 1920s, but in the latter period, the phenomenon has been noticed more widely. To better understand the situation, Zurui Aoa staff member of the Beidou Research Institute and his colleagues examined 82 settlements using satellite data.
Analyzing the period between 2015 and 2022, they found that 45 percent of urban areas are sinking by more than 3 millimeters per year. For about 16 percent of them, the loss exceeds 10 millimeters per year.
The latter, particularly rapid decline, is estimated to affect around 67 million people.
The degree of subsidence is influenced by many factors, including geology and the mass of buildings, but one of the most important factors is the loss of groundwater. As the waters under and near the cities are withdrawn, the soil and the infrastructure begin to crumble. The problem can be observed not only in China, but also in America, among others.
Other factors affecting subsidence include urban transportation systems and mineral extraction and coal mining. In the northern region of Pingdingsan, one of the country’s largest coal-producing areas, the ground is sinking extremely fast, at 109 millimeters per year.
In coastal areas, where sea level rise is also a problem, soil erosion is a huge danger. According to researchers, the land is sinking faster than the sea is rising, and the two processes together threaten hundreds of millions.
The results show that there are effective strategies for slowly reducing subsidence. These include improving water management.
