First published October 4, 2018.
Mexico City is sinking because it pumps huge amounts of water out of the aquifer beneath it, and the soft clay of the old lake bed it is built on compacts as that water is removed. In the fastest-sinking districts the ground has dropped by several tens of centimetres a year, and parts of the city have fallen roughly nine metres (about 30 feet) since the early 1900s.
One popular claim needs correcting straight away. Headlines that said the city was sinking "three feet each year" confused two different measurements: the reported fall of the water table underground and the sinking of the land surface. The ground is not dropping a metre a year across the city. The real rates are lower, vary a lot from place to place, and are still among the most extreme measured anywhere on Earth.
A city built on a drained lake
To understand the sinking, you have to start with the lake. When the Aztec capital Tenochtitlan was founded, it stood on an island in Lake Texcoco, part of a chain of lakes in a high basin ringed by mountains. The Aztecs built dikes to separate fresh water from salty water and to control floods.
After the Spanish conquest, colonial authorities began draining the lakes from the 17th century onward to stop the city from flooding. Drainage continued for centuries, and the city's deep drainage system finished off most of the remaining water in the 20th century. Today only a small fragment of Lake Texcoco survives, near Atenco in the State of Mexico.
What the lake left behind is a thick layer of soft, water-rich clay. Clay like this behaves a bit like a wet sponge: as long as its pores are full of water, it holds its shape. Pump the water out, and the clay slowly squeezes together. Unlike a sponge, it does not spring back.
How groundwater pumping makes the ground drop
Greater Mexico City is home to around 22 million people, according to the 2020 census, and a large share of their water comes from wells drilled into the aquifer under the valley. The rest is brought in from outside the basin, notably through the Cutzamala system, which has to lift water over the surrounding mountains at great cost.
Because more water has been taken out of the aquifer than rain and rivers put back, groundwater levels have fallen over many decades. As water pressure in the clay layers drops, the clay compacts and the land surface sinks with it. Engineers first documented the problem in 1925, according to NASA's Jet Propulsion Laboratory, and it has continued ever since.
Journalist Andrea Noel, speaking to producer Alan Sanchez in a video for the Fusion network, summed up the hard truth: "There's no fixing it. Once land is subsided, it's subsided." She is broadly right. Compacted clay cannot be pumped back up. What can be done is to slow or stop further sinking by taking less water out of the ground.
Julia's Mexico City
What the measurements actually show
Scientists track subsidence with satellite radar (a technique called InSAR) and precise GPS stations. Their results give a clearer and more varied picture than the viral headlines:
- Research at Florida International University, using Italian COSMO-SkyMed radar images, recorded subsidence of up to about 36 centimetres a year in parts of the city.
- NASA's JPL notes that in the 1990s and 2000s some parts of the metro area were sinking about 35 cm (14 inches) a year.
- Early measurements from the joint NASA and Indian NISAR radar satellite, launched in July 2025, showed some areas sinking by more than 2 cm a month between October 2025 and January 2026.
- Overall, parts of the city have dropped about nine metres since the early 1900s, and some estimates put current peak rates near 50 cm a year.
These numbers are dramatic, but they are a long way from a metre a year everywhere. The average hides the most important feature of the problem: some neighbourhoods are sinking quickly, while others, built on firmer ground at the edges of the old lake, barely move.
Why uneven sinking does the real damage
If a whole city sank smoothly and evenly, buildings would ride down together and the main risk would be flooding. The trouble in Mexico City is differential subsidence: neighbouring patches of ground sinking at different speeds.
That unevenness bends and cracks things. It tilts churches and old buildings, including the Metropolitan Cathedral, whose floor visibly slopes. It cracks roads and breaks water and sewer pipes, which then leak and waste even more water. It distorts the tracks of the Metro, raising maintenance costs and flood risks in underground and elevated sections.
One of the most famous illustrations is the Angel of Independence, the golden-winged column on Paseo de la Reforma completed in 1910. Its foundations rest on deep piles, so the monument stayed put while the street around it sank. Over the decades, 14 steps have had to be added to its base to reach it from the pavement.
A water crisis hiding in plain sight
The sinking city has a painful irony at its heart. Mexico City gets heavy summer rains, yet it struggles to supply water, partly because so much of its rainfall runs off paved surfaces into drains instead of soaking back into the aquifer. Leaky pipes, which subsidence makes worse, lose a significant share of the supply before it reaches taps.
Experts, including Noel in the original video, have long pointed to solutions such as rainwater harvesting, repairing leaks, recharging the aquifer with treated water and restoring wetlands. Some of these are already under way. Programmes that install rain-collection systems on homes, for example, have spread in recent years, though they remain small compared with the scale of the problem.
Common myths about the sinking city
- "The whole city sinks three feet a year." No. That figure referred to the reported fall in groundwater levels. Land subsidence is measured in centimetres a year, up to tens of centimetres in the worst spots.
- "It is caused mainly by earthquakes." Earthquakes are a serious danger in Mexico City, and the soft lake clay amplifies shaking, but the long-term sinking is driven by groundwater pumping.
- "The damage can be reversed." Compacted clay stays compacted. The realistic goal is to slow the sinking.
Not just Mexico City
Many large cities face the same pressure on their groundwater, including Jakarta, parts of California's Central Valley and cities in northern China. Early reports of this story credited a "NASA analysis" with finding that four billion people were at risk from falling water tables. That needs a small correction. The four-billion figure comes from a 2016 study in Science Advances by Mesfin Mekonnen and Arjen Hoekstra of the University of Twente, which found that about four billion people face severe water scarcity for at least one month a year.
NASA's contribution was different but just as worrying. A 2015 study led by the University of California, Irvine, using NASA's GRACE satellites, found that 21 of the world's 37 largest aquifers had passed sustainability tipping points between 2003 and 2013, meaning more water was being removed than replaced.
Mexico City is simply the place where the consequences are easiest to see, in tilted cathedrals, bent railway lines and a monument that keeps gaining steps. Watching it sink is a reminder that groundwater is not an endless reserve, and that the ground beneath a city depends on how carefully that water is used.
(The video originally embedded here is no longer available on YouTube.)
Sources: NASA/JPL: NISAR maps extreme subsidence in Mexico City; Florida International University: Mexico City subsidence research; Wikipedia: Mexico City; University of Twente: four billion people affected by severe water scarcity; NASA/JPL: a third of big groundwater basins in distress; original video by Fusion, reported by Andrea Noel and Alan Sanchez; photo: Julia's Mexico City.
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