Scientists assess land subsidence in China’s major cities

Radar observations from satellites can track ground deformation.

Over many years, radar can pick up even relatively small changes on the order of millimeters per year, according to Science.

Ao et al. used satellite observations to determine the extent of land subsidence across 82 major cities in China. They found that about 40 per cent of the land is undergoing moderate to severe subsidence, which adds to the risk of flooding for a large population.

China’s massive wave of urbanization may be threatened by land subsidence. Using a spaceborne synthetic aperture radar interferometry technique, we provided a systematic assessment of land subsidence in all of China’s major cities from 2015 to 2022. Of the examined urban lands, 45 per cent are subsiding faster than three millimetres per year, and 16 per cent are subsiding faster than 10 millimetres per year, affecting 29 and seven per cent of the urban population, respectively. The subsidence appears to be associated with a range of factors such as groundwater withdrawal and the weight of buildings. By 2120, 22 to 26 per cent of China’s coastal lands will have a relative elevation lower than sea level, hosting 9 to 11 per cent of the coastal population, because of the combined effect of city subsidence and sea-level rise. Our results underscore the necessity of enhancing protective measures to mitigate potential damages from subsidence.