Walking into the Zocalo, Mexico City’s vast central square, visitors often feel a subtle and uneasy sense of imbalance: at one end of the square, the majestic Capital Cathedral tilts to one side; the connected church, known as the Metropolitan Temple, tilts in the opposite direction, and the National Palace next to it also appears slightly out of alignment. These "tottering" historical buildings are the most intuitive sign that land subsidence has been accelerating for more than a century: Mexico City is slowly sinking at an alarming rate.
Now, the subsidence process of this megacity is being "tracked" in real time by an unprecedentedly powerful space radar system. This satellite named "Nisar" can penetrate thick clouds and even dense vegetation, capture extremely small deformation changes on the surface, and convert the subtle weekly fluctuations of the ground into high-precision image data. Malin Govolchin, a scientist at NASA's Jet Propulsion Laboratory who participated in the project, said that Nisar has pushed ground radar imaging capabilities to a new level. Almost any change, big or small, will be recorded week by week, which is unique among all existing imaging missions.
This is not the first time humans have observed the sinking of Mexico City from space, but the density of information brought by Nisar is unprecedented. Compared with previous space sensors, this system not only outlines the extension of the subsidence zone more clearly, but also finely depicts the subsidence differences in different landform types. Areas on the edge of cities with complex topography that were difficult to monitor in the past are now included in systematic observations, providing researchers with a more comprehensive risk picture.
Dario Solano-Rojas, an engineer at the National Autonomous University of Mexico, pointed out that this application in Mexico City is just the tip of Nisar's potential. In his view, the same technology can also be used to monitor various geological disasters such as volcanic activity, earthquake deformation, and landslides, providing a new perspective for risk warning in related areas. NASA also emphasized that Nisar has great potential in monitoring the climate crisis, including tracking glacier slippage, observing coastal floods, monitoring forest changes and agricultural productivity, and assessing soil moisture.
Judging from the latest images, the subsidence rate in some areas of Mexico City is so fast that it has ranked among the top in the world. Results from Nisar's joint mission with the Indian Space Research Organization showed that ground subsidence has exceeded 2 centimeters per month in parts of the capital, including the main airport. In the subsidence map drawn from data from October 2025 to January 2026, many areas are marked in dark blue, indicating that the monthly settlement exceeds this warning threshold.
The "Angel of Independence" monument on Reform Avenue in the city center is one of the most tangible evidences of this slow decline. This 36-meter-high monument, built in 1910 to commemorate the centenary of Mexico’s independence, has had to be repeatedly “raised” due to the continued sinking of the surrounding ground. So far, 14 steps have been added. Nowadays, when people look up at this angel statue, the steps under their feet are also silently recording the time scale of the city's "sinking into the center of the earth".
But subsidence has caused not only a dislocation of the landscape, but also a systemic impact on a megacity with a population of about 22 million. From visible building tilts and road undulations to damage to subway systems, the impact of subsidence on urban infrastructure is everywhere. Efraín Obando Shirley, an engineer at the National Autonomous University of Mexico, bluntly said that this process has affected almost all the city's basic systems: street pavements, drinking water distribution pipe networks, tap water supplies, and drainage pipelines have all been damaged to varying degrees.
The existence of subsidence in Mexico City is not a new discovery. This phenomenon was documented as early as 1925. However, its roots go back much further: centuries of over-extraction of groundwater resources. The city and surrounding areas are built on an ancient lake basin, with a soft, clay-like underground soil. When the amount of water pumped from the aquifer below far exceeds natural recharge, the overlying soft soil gradually compacts, and the entire city slowly sinks. Govolchin explained that the current subsidence in Mexico City is mainly caused by this severely imbalanced water pumping process. The aquifer is continuously compressed under the weight of the city, and natural precipitation is far from enough to restore the water volume.
Even today, this underground aquifer supplies about half of the capital’s water. As pumping intensity has continued to rise over the years, the aquifer has shrunk more and more significantly, and the groundwater level is currently falling by about 40 centimeters per year. What's more serious is that a vicious cycle has been formed between this subsidence and water supply: the city continues to "collapse", aging pipelines buried underground are pulled and broken, and a large number of water transmission and drainage pipe networks leak, causing about 40% of the capital's water supply to be lost during the transportation process. If coupled with continued low rainfall caused by the climate crisis, experts warn that Mexico City is accelerating towards some kind of "catastrophic" scenario - large areas of the city may face a moment when the taps collectively run dry.
Faced with the gradually accelerating sinking, practical countermeasures are still limited. Apart from salvage projects such as reinforcing foundations and adding supports to monuments, overall management measures have not really been carried out. Experts expect that the high-resolution subsidence images provided by Nisar will bring this issue to a higher level of attention, thereby promoting stronger public policy discussions and infrastructure investment. However, truly preventing urban sinking itself will be far more difficult than mapping the risks.
"To stop the city from sinking, we have to stop pumping groundwater." Shirley said frankly, "But once we stop pumping, what water should we drink?" Among locals, a slightly self-deprecating but helpless joke is widely circulated: If you can't even drink water, you have to drink tequila instead.