NISAR Satellite Detects Mexico City Subsidence Rates of Up to Half Inch Per Month

She noted that things once learned only by walking everywhere are now captured by this tool, adding that technology is here to help researchers who have spent decades studying the city on foot.

Mexico City's sinking has been documented for more than a century. Engineer Roberto Gayol reported the first finding in 1925, pointing to a large canal and tunnel built to drain water as a potential cause. By the late 1800s, the city was sinking roughly two inches per year, according to a 1995 report by the National Academies of Sciences, Engineering, and Medicine.

The rate accelerated in the 1950s to 18 inches per year, the same report found. Scientists now attribute the subsidence primarily to decades of draining the ancient lakebed aquifer the city was built on. As water is pumped out, the ground above compacts and stays that way, like wet clay squeezed flat and hardened in place.

Not every part of the city sinks at the same rate. Bekaert explained that the compaction causes the ground surface to sink unevenly, with different parts moving at different rates. Parts of Mexico City have lost as much as 30 feet of elevation over the last century, researchers say, while the worst-hit areas have sunk as much as 127 feet.

In a June 15, 2016, file photo, people walked past a slightly tilted historic building in downtown Mexico City, illustrating how the city, built on a drained lake bed, has seen many structures tilt from uneven sinking into soft earth over decades or centuries.

Carreón-Freyre highlighted the urgency of such monitoring beyond Mexico City, citing sinkings in the Philippines at 30 centimeters per year combined with sea level rise. She said what she saw there was really terrible because the two phenomena work together in a very bad way for the population.

Bekaert expressed broader interest in mapping ground motion across coastal zones, where a large proportion of the world's population lives and understanding surface change is particularly important. Scientists say NISAR can now continuously monitor sinking cities anywhere on Earth.