Most populous U.S. metros face subsidence problem

The country’s 28 most populous metros are slowly sinking, according to a study published in the journal Nature Cities.

The land beneath these cities is subsiding, mostly because people are using too much groundwater causing aquifers to collapse. That effect is compounded by the weight of a metropolis, which compacts the underlying soil.

Researchers used satellites to measure how the elevation is changing in cities and found that in every one of them, at least 20% of the urban area is sinking. In 25 cities, at least two-thirds of the area is subsiding, with rates up to 0.4 of an inch each year.

Differential subsidence can be a serious problem for buildings. Where one end of a building sinks a quarter of an inch a year, and the other end sinks, say one-third of an inch, the differential will destabilize the building’s foundation over time.

“The solution to subsidence is to put water back in the ground, what scientists call managed aquifer recharge, which can reinflate the land,” notes a Grist report.