China’s Sinking Cities: 200 Million People at Risk

A recent study has revealed that 45% of Chinese cities are sinking by more than 0.12 inches (3mm) annually, putting hundreds of millions of Chinese citizens at risk.

BBC reported this on the 19th (local time), citing a paper published in Science. About 50 Chinese scientists jointly wrote the paper.

The study, conducted from 2015 to 2022, measured the surface changes of 82 major cities, which account for three-quarters of China’s urban population, using satellite radar. This is the first time satellite data has been used to measure how many cities are sinking across China systematically.

The analysis revealed that nearly half of the urban areas, home to 29% of China’s population, are sinking faster than 0.12 inches (3mm) annually. The population living in these areas is about 270 million. Areas where the average annual subsidence reached 0.39 inches (10mm) also accounted for 16% of the total.

The leading cause identified was excessive groundwater extraction. Excessive groundwater pumping lowers the water table and causes the land above it to sink.

The scientists explained that the impact of land subsidence is more severe along the coast, where sea levels are rising, making these areas more susceptible to storms and flooding.

Urbanization, which increases the cities’ weight, is another factor causing the land to sink. Over time, the weight of accumulating sediment and heavy buildings naturally compresses the soil, leading to subsidence.

Coastal metropolises, including Beijing, Tianjin, Shanghai, and Guangzhou, were identified as particularly at risk. Last year in Tianjin, roads collapsed, and apartments tilted in a residential complex, causing residents to evacuate.

The researchers warned, “If this trend continues, within 100 years, about a quarter of the coast could sink below sea level due to subsidence and rising sea levels, causing massive damage and endangering the lives of residents.”

While they acknowledged that it’s impossible to prevent land subsidence completely, they advised that limiting groundwater extraction is the key to minimizing damage.