Extracting ground water for growing urban populations causes half of China's big cities to sink
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 more modern times, the country is seeing widespread evidence of subsidence in many of the cities that have expanded rapidly in recent decades.
The researchers say that the cities facing the worst problems are concentrated in the five regions highlighted on the map below.
This essentially means the extraction of water underneath or near cities for use by the local population.
In China, the research team were able to associate the extraction of water from over 1,600 monitoring wells with increasing levels of subsidence.
"I think the water extraction is, to my mind, probably the dominant reason," said Prof Robert Nicholls, from the University of East Anglia, who was not involved in the research.
"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."
"But in the 1970s, they provided good piped water from other areas and they also had a law saying you will not use well water and essentially it stopped the subsidence."