Many US Cities Are Sinking. But In Texas, It’s Worse

Cities across the US are sinking,and the problem is most pronounced in Texas, according to a new study.

The research, which examined 28 cities and was published in science journal Nature on Thursday, found all of them were affected by subsidence, a geological phenomenon that increases their exposure to disasters like floods and earthquakes. Urban centers in Texas are among those sinking the most and have some of the largest numbers of buildings facing potential dangers, according to the report.

“We didn’t really expect to see so much” in Texas, said Manoochehr Shirzaei, a professor of remote sensing and environmental security at Virginia Tech and coauthor of the study.

The researchers had previously studied subsidence in coastal areas, where it’s most expected, but expanded their lens inland for the latest study.

While subsidence has natural drivers, humans contribute to it by pumping water from the ground. That drains layers of porous water-bearing rock, which can then no longer hold weight and becomes compact under pressure. Think of how your finger sinks when you place it atop a wrung-out kitchen sponge, except in this case it’s land or even a building that’s settling deeper into the ground.

Oil and gas extractionhas a similar effect, and is likely an additional factor in Texas, according to Shirzaei. Houston, which has the highest rate of subsidence, is sinking at more than 5 millimeters a year on average. The area’s natural geology is likely also playing a role.

While subsidence varies within cities, at least a fifth of each city studied was affected, and that share rose to at least 65% for most of them.

Sinking buildings

The researchers also looked at the threat subsidence poses to buildings, since receding land can wreck their foundations. While most buildings face relatively low risks, more than 29,000 buildings across the 28 cities were classified as high or very high risk. Four of five of the cities with the most risky buildings were in Texas.

The researchers calculated subsidence rates using radar satellites, which emit a signal that bounces back after hitting the ground, allowing them to measure distances over time.

Cities can address subsidence, including by restoring water back into the ground, a strategy known as managed aquifer recharge. Some places, like Orange County in California and areas across Australia, are already doing it. Cities can also increase the elevation of buildings. An extreme example of this can be seen at the Kansai International Airport in Osaka, Japan, which due to sinking sits on adjustable hydraulic jacks.