Heavy buildings & co.

The ground is sinking under China’s cities

The capital Beijing also has to contend with this problem.

(Bild: zhu difeng - stock.adobe.com)

The ground is constantly sinking under many Chinese cities. Researchers are now warning that this is increasing the risk of flooding in the country's metropolitan areas on the coast. In the next hundred years, as much as a quarter of the land could sink below sea level.

The subsidence could have long-term consequences, especially in the densely populated coastal regions, researchers warn in the journal "Science". For large population groups, this means a considerable risk of flooding. In addition, there would be direct damage to buildings and foundations, infrastructure and sewage systems.

The megacity of Beijing is also severely affected by subsidence. It is known from Shanghai that areas of the city subsided by up to three meters in the last century. The research team led by Zurui Ao from South China Normal University in Foshan has now analyzed satellite measurements of 82 major Chinese cities with 74 percent of the country's urban population between 2015 and 2022. Around a third (29%) of the population of these cities is affected by subsidence of more than three millimetres. According to the researchers, a total of 920 million people were living in China's urban areas as of 2020 - an estimated 270 million of them on sinking ground.

Shanghai could also be massively flooded.

(Bild: gui yong nian - stock.adobe.com)

Buildings have a lot of weight
Soil subsidence is associated with a number of factors, including the extraction of groundwater and the weight of buildings. According to the researchers, China has experienced one of the fastest and most extensive urban expansions in human history in recent decades. Even now, an increasing number of cases of subsidence are being reported in large cities. In China, subsidence-related disasters have already caused hundreds of deaths and injuries every year in recent decades, as well as immense economic damage.

"The results underline the need to strengthen protective measures and strictly control groundwater extraction," the study states. Long-term controls and more sustainable water management, as already successfully practised in the Japanese cities of Tokyo and Osaka, could also help to stabilize the subsidence rate in China.

Soil subsidence often caused by humans
Soil subsidence is a phenomenon that causes considerable problems not only in China, but also in many other parts of the world. It is often caused by human activities such as the overuse of groundwater, intensive construction or oil and gas extraction. But natural geological factors also play a role. Cities such as Venice in Italy and Mexico City in Mexico, for example, are known for their problems with subsidence.

In some parts of the world, there are counteracting processes - for example, due to a continuing uplift of land areas freed from the weight of the ice sheet of the last ice age.