Mexico City is subsiding at one of the fastest rates in the world, with some areas — including its main airport — sinking by more than 2cm a month, according to new data gathered by NISAR, a joint NASA–Indian Space Research Organisation radar satellite capable of detecting minute surface changes week by week. The city of roughly 22 million people was built on a drained ancient lake bed, and centuries of groundwater extraction have caused the soft clay soil beneath it to compact, warping roads, cracking metro infrastructure, and tilting landmark buildings such as the Metropolitan Cathedral on the central Zócalo plaza. Engineers warn of a compounding crisis: subsiding ground breaks ageing water pipes, causing an estimated 40% of the city's water supply to leak away, while the aquifer — which still provides about half the capital's water — is shrinking by around 40cm per year, leaving officials with little viable alternative to the very pumping that is accelerating the collapse.