The nation’s largest cities, including San Francisco, are sinking, according to a new study that calls the downward spiraling a widespread and “slow-moving hazard,” threatening thousands of buildings and millions of people.

The 28 cities studied, each with populations of 600,000 or more, averaged just a few millimeters of vertical movement annually. Still, this small amount of sinking adds up over time. In parts of some cities, the movement is as much as 2 inches a year.

Known technically as land subsidence, the phenomenon can cause roads, bridges, utilities, dams and building foundations to buckle and increase the likelihood of flooding. Often it is the result of groundwater pumping.

“Land subsidence matters,” said study lead author Leonard Ohenhen, a postdoctoral researcher at the Columbia Climate School’s Lamont-Doherty Earth Observatory.

About 80% of the land subsidence in the cities studied by Ohenhen and his colleagues is believed to be caused by over-extraction of groundwater. When water is drawn out of the ground it creates empty space, upon which the land above can collapse. This is common in the San Joaquin Valley, where growers have long overburdened aquifers to irrigate thirsty crops. It has also contributed to subsidence in some urban areas, including San Jose and San Diego.

But there are other causes, too. In San Francisco, where groundwater pumping is not an issue, the compaction of filled-in land at such places as Treasure Island, the city’s eastern bayshore and San Francisco International Airport is causing the land to sink.

Some San Francisco compaction sites are experiencing as much as 5 millimeters of annual subsidence, or about a fifth of an inch a year, according to the study. As a whole, the city averaged just under 1 millimeter of sinking.

“Over time, this subsidence can produce stresses on infrastructure that will go past their safety limit,” Ohenhen said. “It’s not to say that all the buildings are going to collapse. It’s to show that if these rates continue over the next 10, 20 or 30 years, these areas are going to be affected.”


The study was published Thursday in the scientific journal Nature Cities.

While the rates of subsidence vary considerably across the country, even within each city, two-thirds or more of the land in 25 of the 28 big cities studied is sinking, according to the paper. This area is home to 34 million people and 29,000 buildings deemed to be at significant risk of damage.

In the other cities, at least 20% of the land is subsiding.

San Diego has the greatest rate of subsidence among California’s four cities with populations above 600,000, according to the study. The city, on whole, is dropping a little more than 1 millimeter annually. Los Angeles is slipping just under 1 millimeter each year while San Jose averaged no annual subsidence.

San Jose was among a handful of cities where uplift in some areas offset sinking in others. The study did not identify what was causing the ground to rise but it suggested that one driver could be the recharging of groundwater by swollen rivers and creeks.

The nation’s fastest-sinking city is Houston, according to the study, with an average of 5 millimeters of annual subsidence. Two other Texas cities, Fort Worth and Dallas, were close behind. The authors speculate that pumping oil and gas from the ground, with the same effect as groundwater extraction, contributed to the state’s high rates of subsidence.

The authors of the study included researchers from Virginia Tech, the Netherlands Organisation for Applied Scientific Research, UC Berkeley, Texas A&M University, University of Colorado Boulder, Brown University and United Nations University. (Source: The San Francisco Chronicle)

Story Date: May 11, 2025