Nearly half of China’s major cities are sinking, posing a significant risk of flooding to millions of people, according to a recent study published in the journal Science.
The study found that 45 percent of China’s urban land is subsiding at a rate of over 3 mm per year, while 16 percent is sinking at more than 10 mm per year. Researchers examined 82 Chinese cities with populations exceeding 2 million, using satellite radar pulses to detect changes in the ground’s elevation between 2015 and 2022.
Shanghai, China’s largest city, continues to sink despite already having subsided by about 3 meters over the past century. Beijing and Tianjin are among the other major cities experiencing significant subsidence.
Robert Nicholls, a professor of climate adaptation at the University of East Anglia, who was not involved in the study, told the BBC that water extraction is likely the main reason for this subsidence. “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,” he said.
The study suggests that the key to resolving this issue may be controlling groundwater extraction over the long term. Nicholls warned that subsidence can threaten the structural integrity of buildings and critical infrastructure, as well as exacerbate the impacts of climate change, especially in coastal cities where it amplifies sea-level rise.
According to Reuters, subsidence already costs China over 7.5 billion yuan (about $1.05 billion) annually. The problem, however, is not limited to China. A paper published in February indicated that 6.3 million square kilometers of land worldwide are at risk of subsidence, with Indonesia being one of the most affected countries.
In the United States, more than 17,000 square miles across 45 states are also experiencing subsidence, according to the United States Geological Survey (USGS). The USGS reports that more than 80 percent of subsidence cases in the US are linked to underground water extraction, adding, “The increasing development of land and water resources threatens to exacerbate existing land-subsidence problems and initiate new ones.”
This article was originally published by Business Insider.
