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Nearly half of China’s major cities are sinking because of water extraction and the increasing weight of their rapid expansion, researchers say.
Some cities are subsiding rapidly, with one in six exceeding 10mm per year.
China’s rapid urbanisation in recent decades means far more water is now being drawn up to meet people’s needs, scientists say.
In coastal cities, this subsidence threatens millions of people with flooding as sea levels rise.
China has a long history of dealing with subsiding land, with both Shanghai and Tianjin showing evidence of sinking back in the 1920s. Shanghai has sunk more than 3m over the past century.
In more modern times, the country is seeing widespread evidence of subsidence in many of the cities that have expanded rapidly in recent decades.
To understand the scale of the problem, a team of researchers from several Chinese universities have examined 82 cities, including all with a population over 2 million.
They’ve used data from the Sentinel-1 satellites to measure vertical land motions across the country.
Looking across the period from 2015 to 2022, the team was able to work out that 45% of urban areas are subsiding by more than 3mm per year.
Around16% of urban land is going down faster than 10mm a year, which the scientists describe as a rapid descent.
Put another way,
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