NASA Radar Tracks Mexico City Sinking

The problem has deep historical roots. Mexico City was built on an old lake bed, so the ground is soft clay that shrinks when water is pumped from the aquifer underneath. Marin Govorčin, a scientist at NASA's Jet Propulsion Laboratory, says the city takes groundwater far faster than rain can refill it. Today, about half of the capital's water still comes from this shrinking underground reservoir, and the water table is falling by roughly forty centimetres each year. Records of the sinking go back to 1925, when the rate was already alarming.

The damage is visible across the city. Churches lean, pavements crack and the underground metro suffers regular problems. The Metropolitan Cathedral tilts to one side, while the Angel of Independence has had fourteen extra steps added to its base since 1910 as the ground around it has fallen. Engineers warn that ageing pipes lose about forty per cent of the city's drinking water through leaks. The NISAR team plans to map risk building by building, but stopping the sinking would mean cutting off water to millions.