According to a study published in the journal Nature City, the largest cities in the United States are slowly sinking, not just cities near the ocean. The satellite-based study shows that all 28 U.S. cities have incubation periods of more than 600,000 people, making infrastructure increasingly risky in rapidly developing urban areas.
The researchers used satellite data to study vertical land movements in large American cities and found that they all sunk to some extent. Groundwater extraction appears to be the most common culprit, with its impact on land movements directly affecting the infrastructure of the most populous communities in the country.
“As cities continue to grow, we will see more cities expand into lurking areas,” Leonard Ohenhen, a postdoctoral researcher at the Columbia Climate School of Lamont-Doherty Earth Observatory, said in a university statement. “As time goes by, this settlement creates pressure on the infrastructure, which will exceed its security limits.”
Ohenhen and his colleagues used recent satellite data to map vertical land movements in the most populous cities in the United States and analyzed them in a system’s 90-square-foot (28-square-meter) grid. Although many people hear that large coastal cities such as New Orleans are sinking, the study shows that even inland municipalities, including Denver, Oklahoma and Fort Worth, can give up.
Overall, the results show that 25 of the 28 cities analyzed were sinking at least two-thirds of the land. Houston is the fastest sinking metropolis, with over 40% of its land land dropping more than 0.20 inches (5 mm) while 12% dropping 12%. Cities including New York, Las Vegas, Washington, D.C. and San Francisco also have relatively small but quick-linked areas.
This helps with different movements: the areas sink at different speeds, or some areas gradually decrease, while others increase. This unbalanced movement can harm the infrastructure by causing the building to tilt.
While only about 1% of recorded areas are experiencing a strong enough differential action to impact infrastructure, these areas tend to be the most urbanized, with about 29,000 buildings. According to the study, 45 buildings in San Antonio are at high risk, and 71 buildings in Austin are also at high risk, with 143 in Fort Worth and 167 in Memphis. More detailed research is needed to assess the specific risks of individual buildings, Ohhenhen said in the statement.
“The risk is manifested only when the high settlement rate drops to the height of land below the critical threshold, and subordinate-induced infrastructure damage occurs even with smaller changes in land movement.” However, sunken land is often more susceptible to flooding.
By analyzing groundwater extraction together with vertical land movement, the researchers determined that this activity was the reason for 80% of the literature accumulation. That’s because when humans take water out of the aquifer (the porous rock layer that holds groundwater), the pores collapse, lowering the surface above it. The researchers believe that this phenomenon will only worsen in some areas due to factors such as population growth (meaning increased water demand) and climate-driven drought.
But there are other forces that are working. Some sinking areas are still recovering from the uplifts caused by long-term ice age glaciers within North America. The huge weight of buildings can also affect land movement in some cities (New York cough).
Ultimately, the researchers hope their research will stimulate the impetus for mitigation efforts, which may include raising land, building renovations and renewal construction regulations.
“With just saying that this is a question we can answer, solve, mitigate, adapt,” Ohhenhen concluded. “We have to turn to solutions.”
