28 Major U.S. Cities Are Sinking, Mostly Because of Groundwater Withdrawal, Study Finds

A new study has revealed that 28 of the most populated cities in the U.S. are sinking, which can increase flood risks and weaken infrastructure. Further, researchers determined that 80% of total sinkage could be attributed to groundwater withdrawal for human use.

According to the study, published in the journal Nature Cities, about 34 million people in the biggest cities in the U.S. are being impacted by sinkage, with at least 20% of all the urban areas studied showing signs of subsidence.

Eight cities in the U.S. make up 60% of the 34 million people living on subsiding land. According to the study, these cities also have sinkage of more than 3 millimeters per year and have collectively experienced more than 90 flooding events since 2000.

In 25 of the 28 cities in the study, at least two-thirds of the urban area is sinking. Houston is the most affected, with 42% of the city sinking by more than 5 millimeters per year and 12% of the city sinking by more than 10 millimeters per year. Some parts of the city are sinking by up to 5 centimeters, or around 2 inches, each year.

“As cities continue to grow, we will see more cities expand into subsiding regions,” Leonard Ohenhen, lead author of the study and a postdoctoral researcher at the Columbia Climate School, said in a statement. “Over time, this subsidence can produce stresses on infrastructure that will go past their safety limit.” 

While using groundwater is a major contributor to sinkage, the report noted that the weight of buildings and infrastructure and activities such as extracting oil and gas are also contributing to subsidence. In Texas, in particular, sinkage is affected by fossil fuel extraction.

Some cities, including Jacksonville, Florida; Memphis, Tennessee; and San Jose, California, are experiencing variations in sinking, or differential motion. These cities may have areas sinking at different paces or may have areas that are rising while other nearby areas sink. Rising land could be linked to recharging aquifers, the Columbia Climate School reported.

“Unlike flood-related subsidence hazards, where risks manifest only when high rates of subsidence lower the land elevation below a critical threshold, subsidence-induced infrastructure damage can occur even with minor changes in land motion,” the authors explained. “The latent nature of this risk means that infrastructure can be silently compromised over time, with damage only becoming evident when it is severe or potentially catastrophic. This risk is often exacerbated in rapidly expanding urban centers.”

Cities with the highest risk of infrastructure damage because of differential motion include three cities in Texas — San Antonio (1 in 45 buildings face high risk), Austin (1 in 71 buildings), and Fort Worth (1 in 143) — as well as Memphis, Tennessee (1 in 167).

Subsidence is a widespread problem that is also impacting rural areas and cities outside the U.S. As Grist reported, agricultural areas around the California Aqueduct sunk by around 8.5 meters (27.89 feet) from 1926 to 1970 because of excessive groundwater withdrawal. Drought events in the years following have led to additional water pumping that continued to contribute to sinkage in the region. Subsidence is most notable in Mexico City, where parts of the urban area are dropping as much as 20 inches per year, Grist reported.

The authors hope that their findings can help cities better respond and prepare for sinkage, such as by installing artificial wetlands and other drainage solutions and retrofitting infrastructure for higher resilience.

“As opposed to just saying it’s a problem, we can respond, address, mitigate, adapt,” Ohenhen said. “We have to move to solutions.”