Mexico City is sinking at an alarming rate, with some areas subsiding by more than 2cm a month, according to data from a powerful new NASA radar system. The phenomenon, which has been ongoing for over a century, is causing historic buildings to tilt, roads to warp, and underground infrastructure to crack.
The Nisar satellite, a joint mission between NASA and the Indian Space Research Organisation, can detect minute changes in Earth's surface even through thick vegetation or cloud cover. It has provided the most detailed view yet of the sinking, revealing how it spreads across different types of land in the metropolis of about 22 million people.
Scientists say the subsidence is primarily caused by the over-extraction of groundwater from the aquifer beneath the city. Mexico City was built on an ancient lake bed, and as water is pumped out, the soft clay-like soil compacts under the weight of the city. The aquifer still supplies about half of the capital's water, but the water table is shrinking by about 40cm a year.
This creates a vicious cycle: as the city sinks, ageing water pipes crack and leak, causing an estimated 40% of water to be lost. Combined with low rainfall due to climate change, the situation is worsening. The Angel of Independence monument, completed in 1910, has had 14 steps added to its base as the land around it has sunk.
Beyond Mexico City, the Nisar system can monitor volcanoes, earthquakes, landslides, and climate change impacts. Experts say it will open up new possibilities for studying Earth's surface changes globally.
