Up to 22 cm per year: why the world's major cities are gradually sinking

Whether in Mexico City, the Iranian city of Isfahan or Medan, Indonesia, the ground in many cities around the world is gradually sinking. This phenomenon, called subsidence, can damage buildings, underground sanitation and wastewater evacuation networks, but also increase the risk of flooding along coastlines or in urban centers crossed by waterways.

A study published on October 12 in the journal Nature Cities assesses the extent of this phenomenon. A team of researchers from Chinese universities carried out unprecedented mapping of land subsidence in 465 cities with more than a million inhabitants around the world, using satellite data collected between 2014 and 2023 which they analyzed by radar interferometry. This technique, called InSAR, makes it possible to measure ground movements over time by comparing satellite images taken on different dates. “By repeating the observations at the same…