chronicle of a collapse announced and recorded almost live by NASA
Mexico City faces one of the most complex geological challenges that exist and it is not earthquakes: it is subsidence accelerated by human activity. What’s that? The slow and progressive sinking of the soil. One of the causes is the extraction of too much water from the subsoil because that water partly holds the ground from within. If there is no water, the sediments are compacted by gravity and as a result, the surface sinks. Mexico City has been sinking for more than a century for this reason and the recent NISAR satellite mission, a collaboration between NASA and its Indian counterpart ISRO, has launched unprecedented surveillance that is already bearing fruit: the most detailed and recent cartography of this phenomenon in the Mexican capital to monitor its sinking almost in real time. It is more than a map: it is a survival tool for a city inhabited by more than 20 million people. Mexico City sinks. The first time subsidence was reported in Mexico was in 1925. The data from 1898 to 2005 show a constant subsidence throughout the period, with a maximum rate of 40 centimeters per year between 1998 and 2002. It is neither new nor something small and, furthermore, it is a cumulative and mostly irreversible process. So Mexico City is deforming. Sentinel-1 data they showed that the soil surface sinks at a rate of 35 cm per year within the city, while the peripheral areas suffer a slight rise of about two centimeters per year as an elastic response to this loss of water mass. The new NISAR data barely covers three months (from October 2025 to January 2026) and is as easy to read as it is alarming: the dark blue tone marks those areas that sink more than 2 centimeters per month due to subsidence. Map of the subsidence of Mexico City. POT Why is it important. The problem is one of public safety and economics. The Economist echoes from a Water Engineering and Management study that quantifies the structural damage derived from subsidence: about 67,926 million pesos per year (about 3,312 million euros) in pipes, breakdowns, building fractures, among others. It might seem that the fact of sinking itself is the worst, but what is truly destructive is the difference in speed between those areas that go down faster than others, which causes progressive damage to infrastructure while generating structural tensions. criticisms for infrastructure design. In addition to material damage, subsidence alters the seismic response of the soil, increases the risk of serious flooding by modifying the natural drainage of the basin and favors the migration of salts and contaminants into aquifers, which affects water quality. In short, it raises alarm bells about a future water crisis. Context. The origin of the problem is a combination of natural geological factors and historical urban planning decisions. Mexico City was built on the ancient bed of Lake Texcoco, drained by the Spanish conquistadors. When the lake was drained, the city was settled on its old bed, formed by lacustrine clays of volcanic and organic origin. Under natural conditions these clays supported the lake ecosystem without collapsing. However, the development of the city and water extraction has caused the balance to be broken: the silt is compacted and causes the soil to contract and sink. The urban growth of Mexico City prevents rain from recharging the aquifers because more and more soil is covered by impermeable surfaces such as asphalt. It is a vicious circle: there is less natural recharge of the aquifer, which forces more water to be pumped, compaction accelerates and aggravates the subsidence, damaging infrastructure. There is no turning back. When the effort of supporting the city on its shoulders exceeds the pre-consolidation stress (the resistance limit of the clay), the mineral sheets collapse and rearrange themselves definitively. It’s a path of no return: Even if water were stopped being extracted tomorrow, a good part of the accumulated sinking cannot be reversed. The city has literally lost meters of height that it will never recover. What can be controlled is the damage, which involves a change in water management where reducing dependence on aquifers is essential. Of course, it implies looking for other water resources such as transfers or recycling water, in addition to facilitating the penetration of water into the subsoil. These measures will not reverse the damage caused, but at least they would slow down the sinking and offer an alternative access to water for a megacity. The technology behind the map. The satellite NISAR It is the first to carry two synthetic aperture radar instruments at different wavelengths and is capable of monitoring the Earth’s land and ice surfaces twice every 12 days thanks to a huge 12-meter diameter antenna reflector. The technique used is called SAR interferometry (InSAR) and consists of comparing two radar images taken at different times: by measuring the phase changes of the signal, ground displacements of just millimeters can be detected. The great advantage of NISAR over its predecessors is its L band (wavelength of about 24 centimeters), which allows it to work even in terrain with dense vegetation or high humidity where other radars such as the Sentinel-1 lost quality. This tool turns NISAR into a global early warning system for cities facing similar risks. 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