Mexico City Keeps SinkingBy Rodrigo Brugada | Wed, 05/19/2021 - 19:33
Mexico City is sinking as a result of a geological phenomenon called groundwater-related subsidence, which usually happens when the land begins to compact because too much water is drawn from the underground. The sinking, which is likely to affect most of the Mexico City Metropolitan Area, is unequal and putting the area’s infrastructure under different stresses.
According to UNAM's Geophysics Institute, sinking in parts of the city exceed 370 mm/year, causing structural harm to homes and urban infrastructure. Eos states that vast portions of the ground beneath the city are steadily compacting after being drained of water a long time ago. Eos argues that the ground will continue to compact for about 150 years, adding up to 30 meters of subsidence to the damage caused during the 20th century.
Mexico City's case, unlike subsidence in many other cities of the world, does not seem only to reflect local groundwater pumping rates. Instead, it reflects the steady compacting of the ancient lake bed on which the city was built. The origins of the problem lie in Mexico City's bad foundation. While the Aztec people built their capital city of Tenochtitlan on an island in Lake Texcoco in the Valley of Mexico, a basin surrounded by mountains, the Spanish arrival marked the start of many attempts to desiccate the valley. And while the Aztec people had managed the land and the lake sustainably, the Spanish attempts at modifying the environment started a chain reaction that still affects us to this day.
During the Conquista, the Spanish began draining the lake and erecting buildings on its top. This water extraction drove groundwater deeper and the clay-rich lake bed became the surface on which to build. Its very fine mineral grains have since been steadily repacking themselves more tightly, causing the ground to shrink and subside. And because the city was built on deposits of variable size, it subsides unevenly. This is further discussed in a paper published by the Journal of Geophysical Research.
Two authors of this paper discussed this issue with Wired. They stated that while halting groundwater extraction can stop the sinking, because of how this phenomenon works parts of Mexico City kept on sinking even after water extraction there has ceased. This would mean that any lost elevation is lost forever and the capacity of the aquifer to store water is severely diminished, adding to a pressing problem regarding water scarcity and hydric stress.
This phenomenon follows and adds to several crises for Mexico City's population, composed of over 9.2 million people. The problem is also likely to affect the almost 22 million people living in the Mexico City Metropolitan Area. This sinking and its social effects are also unequal. If the whole city sank uniformly, it would undoubtedly be a problem. Still, because some areas are sinking faster than others, the two zones' infrastructure is sinking unequally and causing structural damage that threatens to put all structures under different stresses. The zones most at risk are the periphery of the city, which are also the most vulnerable areas in other regards, as shown by the National Risk Atlas. Mexico City is a metropolis of hundreds of square kilometers of roads, buildings and infrastructure under perpetual strain. No matter the efforts to bring maintenance, things will keep on breaking if the underlying issue is not addressed. And while the government might be able to spend money to palliate this crisis, most homeowners cannot.