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Nearly half of China's major cities are sinking, putting millions of local residents at risk of flooding, according to a new study published this week in the journal Science.
The study found that 45% of China's urban land is subsiding faster than 3 mm per year, while 16% is subsiding at a rate of more than 10 mm per year.
The study authors looked at 82 Chinese cities with a population of more than 2 million and used radar pulses from satellites to detect any changes in the distance between the satellite and the ground.
They then measured how the height of cities changed between 2015 and 2022.
They found that China's largest city, Shanghai, continues to sink, even though it has already sunk by about 100m over the past 3 years.
Cities such as Beijing and Tianjin were also particularly affected.
Reasons
There are a number of factors leading to subsidence, but Robert Nicholls, a professor of climate adaptation at the University of East Anglia who was not involved in the study, told the BBC he believed water extraction was "probably the dominant cause".
“In China, many people live in areas that have been relatively recently deposited, geologically speaking. So when you extract groundwater or drain soils, they tend to subside," he said.
The article also suggests that the solution to the problem "may lie in long-term, sustainable control of groundwater extraction."
In a commentary article also published in Science, Nicholls warned that "subsidence threatens the structural integrity of buildings and critical infrastructure, and exacerbates the effects of climate change in terms of flooding, particularly in coastal cities where it exacerbates sea-level rise." .
Land subsidence is already costing China more than 7,5 billion yuan, which is about $1,05 billion a year, according to Reuters.
However, the problem is not limited to China.
In another document published in February, it is said that about 6,3 million sq. km, or about 2,4 million square meters. miles, land around the world is at risk of subsidence, with Indonesia being one of the most affected countries.
According to the United States Geological Survey (USGS), the problem also affected parts of the United States, where more than 17 square miles of land in 000 states were directly affected.
According to the USGS, more than 80 percent of identified subsidence cases in the US are due to groundwater exploitation.
"The growing development of land and water resources threatens to exacerbate existing problems of soil subsidence and the emergence of new ones," the report added.
