Nearly half of China’s major cities are suffering “moderate to severe” levels of subsidence, putting millions of people at risk of flooding especially as sea levels rise, according to a study of nationwide satellite data released on Friday (Apr 19).
The authors of the paper, published by the journal Science, found 45 per cent of China’s urban land was sinking faster than 3mm per year, with 16 per cent at more than 10mm per year, driven not only by declining water tables but also the sheer weight of the built environment.
With China’s urban population already in excess of 900 million people, “even a small portion of subsiding land in China could therefore translate into a substantial threat to urban life,” said the team of researchers led by Ao Zurui of the South China Normal University.
Subsidence already costs China more than 7.5 billion yuan (US$1.04 billion) in annual losses, and within the next century, nearly a quarter of coastal land could actually be lower than sea levels, putting hundreds of millions of people at an even greater risk of inundation.
“It really brings home that this is for China a national problem and not a problem in just one or two places,” said Robert Nicholls at the Tyndall Centre for Climate Change Research at the University of East Anglia. “And it is a microcosm of what is happening around the rest of the world.”
The northern city of Tianjin, home to more than 15 million people, was identified as one of the worst-hit. Last year, 3,000 residents were evacuated after a “sudden geological disaster” that investigators blamed on water depletion as well as the construction of geothermal wells.
