China's large megacities are rapidly declining

Almost half of China's major cities are sinking due to groundwater extraction and the weight of buildings from their rapid growth, researchers say.
Some cities are sinking fast, with one in six sinking more than 10mm. annually.
China's rapid urbanization in recent decades means that much more groundwater is now being extracted 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 problems with landslides, with Shanghai and Tianjin showing signs of subsidence as far back as the 1920s. Shanghai has sunk by more than 3 m in the last century.
More recently, the country has seen widespread evidence of decline in many of the cities that have grown rapidly in recent decades.
To understand the scale of the problem, a team of researchers from several Chinese universities studied 82 cities, including all with a population of more than 2 million people.
They used data from the Sentinel-1 satellites to measure vertical ground motions across the country.
Looking at the period from 2015 to 2022, the team was able to find that 45% of urban areas subsided by more than 3 mm. annually.
About 16% of urban land slides faster than 10 mm. per year, which scientists describe as rapid.
Put another way, this means that 67 million people live in rapidly sinking areas.
The extent of subsidence is affected by a number of factors, including geology and the weight of buildings. But according to the authors, the main element is the loss of groundwater./BGNES