China is facing a serious problem of sinking as almost half of the country’s cities are subsiding. A new study of satellite data warns that millions are at risk of the effects of flooding, and one of the factors to blame is water extraction.
A recent study on satellite data for 82 cities for the period from 2015 to 2022 has revealed that half of the cities in China face the risk of sinking due to excessive water extraction. According to the paper published in the journal, Science, around 45% of cities in China are sinking by over 3mm per year. Furthermore, one out of every six cities in the country is sinking by over 10mm per year, putting over 67 million people at risk. Overall, China is already losing 7.5 billion yuan or US$1.04 billion annually due to subsidence, and the country is facing the risk of having almost a quarter of its coastal lands lower than sea levels in the forthcoming decades.
According to the study, the cities at the highest risk of subsiding are located in five regions. Tianjin, with a population of over 15 million, is among the worst hit cities. In 2023, it experienced a geological disaster when over 3000 residents were forced to move out of their homes. Investigations concluded that the reasons for the disaster were the construction of geothermal wells as well as water depletion. Another large city, Shanghai, has already sunk by almost 3 meters in the last century.
Regions at highest risk
Source: BBC
The factors that impact the level of subsidence of various Chinese cities are different but include the weight of buildings and the geology of the area. However, scientists analyzing the satellite data conclude that the biggest factor is groundwater loss that is driven by the extraction of water to meet the population’s needs.
Robert Nicholls, a researcher from the University of East Anglia, although not a contributor to the paper, commented on the outcomes of the study, saying:
“I think water extraction is, to my mind, probably the dominant reason. In China, there are lots of people living in areas that have been fairly recently sedimented, geologically speaking. So, when you take out groundwater or you drain the soils, they tend to subside.”
The problem of subsidence due to water extraction is not only common in China; other parts of the world, including urban areas such as Delhi, Mexico City, and Houston, also face the same problem. Another study released in February showed that, worldwide, an area of approximately 6.3 million square is in danger of sinking. One of the worst hit countries is Indonesia where its capital has already seen a big part of its land sinking below sea level.
According to Robert Nicholls, this problem can be stopped immediately, and therefore subsidence adaptation and mitigation should be taken very seriously. He advised that cities facing the problem should follow Tokyo’s lead where, having subsided by around 5 meters before 1970, sinking was only halted after the government imposed a ban on groundwater extraction.
