The survey reveals that all of the largest cities in the United States have sunk. Groundwater pumping is the main cause of most

A new study of 28 most populous US cities finds that everything is sinking to some degree. The city contains much of the interior, not just the coastal ones where relative sea levels are of concern. Furthermore, using new granular data, this study found that some cities were sinking at different speeds in different locations, or sinking at one location and rising elsewhere, potentially introducing stress that could affect buildings and other infrastructure.

The authors state that large-scale ongoing groundwater extraction is the most common cause of movement on these lands, but other units work in several locations.

This study has been published in the journal Nature Cities.

“As cities continue to grow, we will see more cities expand into calming regions,” said Leonard Ohenhen, a postdoctoral researcher at Lamont-Doherty Earth Observatory at the Columbia School of Climate. “Over time, this subsidence can cause stress on infrastructure that exceeds safety limits.”

Fast-sinking coastal metropolitan cities such as Jakarta, Venice and New Orleans have already attracted great attention, with several recent studies showing that many places have subsided along the US East Coast and elsewhere. However, most studies rely on relatively sparse data spread over a wide area to draw a wide picture.

Looking at all US cities with populations over 600,000, the new study uses recent satellite data to map land movements perpendicular to millimeters of a grid of just 28 meters (approximately 90 feet) squares. The authors found that in 25 of the 28 cities more than two-thirds of their area have sunk. Overall, around 34 million people live in affected areas.

The fastest city is Houston, with over 40% of its area exceeding 5 millimeters (about 1/5 inch) a year, with 12% sinking at twice that rate.

Some local spots fall to 5 cm (2 inches) a year. Two other Texas cities, Fort Worth and Dallas, aren’t too late. Localized fast zones elsewhere include areas around Lagardia Airport in New York, as well as parts of Las Vegas, Washington, DC and San Francisco.

In addition to measuring changes in surface release, the researchers analyzed county-level groundwater withdrawal of the affected area. Correlating this with land movement, they determined that groundwater removal for human use was the cause of 80% of the overall sink.

Generally, this occurs when water is drawn from an aquifer made up of fine grain sediments. Unless the aquifer is replenished, the pore space previously occupied by water will eventually collapse, leading to compression below, allowing it to sink onto the surface. In Texas, the issue is exacerbated by oil and gas pumping, the paper says.

Researchers say the continued population growth and water usage combined with climate-induced drought in some regions is likely to exacerbate settlement in the future.

In some areas, the forces of nature are at work. In particular, the weight of the towering ice sheet, which occupied most of North America’s interior until about 20,000 years ago, inflated the land along the edge upwards.

Even today, as the ice has passed, some of these bulges still subside at a rate of 1-3 millimeters each year. The cities affected include New York, Indianapolis, Nashville, Philadelphia, Denver, Chicago and Portland.

Even the vast weight of a building may be at the expense of it. A 2023 survey found that over one million New York buildings are pushing hard on the planet, contributing to the ongoing subsidence of the city.

A more recent separate study found that some buildings in the Miami area have been partially sunk due to underground disruption caused by the construction of new buildings nearby.

A new study found that eight cities (New York, Chicago, Los Angeles, Phoenix, Houston, Philadelphia, San Antonio and Dallas) account for more than 60% of people living on the sinking land. In particular, these eight cities have seen more than 90 serious floods since 2000, perhaps driven in part by lowering the topography.

Another important finding: in some cities, adjacent areas sink at different speeds, or even sinking while others rise. Upward movements possibly caused by rapid charging of aquifers near rivers or other sources. (The uplifts in certain regions are actually more than a supplement to the overall sink of the three cities: Jacksonville, Florida, Memphis, Tennessee, and San Jose, California)

As the authors point out, when the entire urban area is up and down evenly at the same speed, differential movement is an issue, as it minimizes the risk of stress on building foundations and other infrastructures. However, if the structure is exposed to an array of uneven vertical motion, it can experience dangerous slopes.

“Unlike flood-related subsidence risks, risks only appear when a high percentage of subsidence falls below the significant threshold for land rise, but even slight changes in land movement can cause subsidence-induced infrastructure damage,” the author writes.

The study found that only about 1% of the total land area of ​​28 cities are within zones where differential movements can affect buildings, roads, rails and other structures. However, these regions tend to be in the dense urban cores, and currently contain around 29,000 buildings.

The most dangerous city in this respect is San Antonio, and researchers say one of the 45 buildings is affected by a high risk. Austin (1/71); Fort Worth (143) and Memphis (167).

The results of the individual structures of these regions are unknown. Perhaps more detailed research is needed, Ohenhen said.

Previous studies of 225 US buildings collapse between 1989 and 2000 found that only 2% were directly attributable to subsidence. However, the factors behind 30% have been designated as unknown, suggesting that subsidence may have played a greater role, according to a new study.

This paper concludes that cities should use this new information to focus on solutions. They say in many places, floods can mitigate flooding, strengthen drainage systems and reduce them with green infrastructure such as artificial wetlands.

Cities that are susceptible to slope risk can focus on remodeling existing structures, integrating land movements into building standards, and limiting new buildings in most threatened areas.

“In contrast to saying that’s the problem, we can respond, deal with it, mitigate and adapt,” Ohenhen said. “You need to move to the solution.”

The study was co-authored by researchers at Virginia Tech, an applied science research institute at UC Berkeley, Texas A&M University, University of Colorado Boulder, Brown University, United Nations University, and University of California, Berkeley.