Mexico City Sinking Tracked by NASA Radar

The roots of the problem stretch back centuries. Built on an ancient lake bed, much of Mexico City rests on soft, clay-like soil that compacts whenever water is pumped from the aquifer below. According to Marin Govorčin, a scientist at NASA's Jet Propulsion Laboratory, the city extracts groundwater far faster than rainfall can replenish it, and roughly half of the capital's water still comes from this shrinking underground reservoir. Formal records of subsidence date from 1925, but historical estimates suggest the rate climbed from about two inches a year in the late nineteenth century to eighteen inches by 1950. Today scientists say the water table is dropping by roughly forty centimetres annually, accelerating the descent.

The consequences are visible across the city: leaning churches, warped pavements, cracked drainage pipes and damage to the underground metro. The Metropolitan Cathedral leans noticeably, and at the Angel of Independence its base has been raised by fourteen extra steps since 1910 as the surrounding ground has dropped. Engineers warn that ageing pipes now leak about forty per cent of the city's drinking water, deepening a looming shortage. The NISAR team hopes future imagery will allow building-by-building risk assessments. Stopping the sinking, however, would mean halting groundwater extraction and leaving residents without taps. As one local engineer joked, if the city cannot drink water, perhaps it must drink tequila instead.