Mexico City – one of the largest metropolises globally and the home to over 21 million people – is facing a daunting challenge as it continues to sink into the ground at an alarming rate of 30 centimetres per year, according to a recent study published in Advancing Earth and Space Science.
This subsidence, which has persisted for over a century, has intensified in recent years, reaching a staggering half a metre annually.
The primary culprit behind this phenomenon is the extensive extraction of underground water, with 70 percent of the city’s drinking water sourced from aquifers located in a basin. The quest for water has inadvertently led to the city’s gradual descent into the ground.
The city’s history plays a significant role in this subsidence. Originally established on the Aztec city Tenochtitlán and Lake Texcoco, the Spanish arrival in the 16th century led to the destruction of protective walls that prevented flooding.
As the lake was drained, the city began sinking gradually over time.
In the 20th century, authorities witnessed a spike in subsidence from 9 to 29 centimetres in the 1950s, prompting measures such as a prohibition on drilling into the ground for water extraction.
However, in the last two decades, Mexico City has experienced a subsidence of 10 metres, averaging 50 centimetres per year.
Researchers employed interferometry and radar studies to analyse the situation, revealing that the damage is almost irreversible due to the weight of the city and its shallow foundations causing soil compaction.
According to the study, unless water levels rise significantly, the subsidence is likely to persist. The potential for an additional descent of 30 metres is a looming threat, contingent on the absence of a severe water crisis.
This concerning situation is exacerbated by the ongoing water crisis that residents have been grappling with since November 2023.
The heart of Mexico City is the most affected, with ancient constructions facing structural damage. The northwest area is comparatively less impacted, stressing the need for alternative water policies in the face of this crisis.
The study concludes that the socio-economic landscape of the Mexico City metropolitan area is greatly influenced by the consequences of land subsidence. The migration of low-quality water to the productive aquifer raises concerns about water quality, setting the stage for a potential water crisis with far-reaching implications for the region.
Manoochehr Shirzaei, a geophysicist at Virginia Tech and a coauthor of the new study, said: “One of the great challenges surrounding Mexico City’s subsidence is the availability of groundwater level data.”
UNAM geological engineer Darío Solano agreed. Although public authorities such as SACMEX and the National Water Commission (CONAGUA) have a history of opacity in publishing this type of data, he said, the information exists and can be accessed by direct request through online data transparency systems.
Continued research into Mexico City’s subsidence is important to keep attention on a problem that often remains neglected, Cabral said.
“All research that … indirectly puts the magnifying glass on this [subsidence] process and on the fact that we must do something to address it is very welcome,” Cabral said.
