The study, published this week in the journal Nature Cities, provides the most precise mapping yet of vertical land movements, utilizing satellite data capable of detecting shifts down to the millimeter across 28-meter (90-foot) square grids. The researchers found that in 25 of the 28 cities, at least two-thirds of the land area is subsiding. An estimated 34 million people live in these affected zones.
Houston stands out as the fastest-sinking major city in the U.S., with over 40% of its area subsiding at more than 5 millimeters (about 1/5 inch) per year, and 12% dropping at twice that rate. Some localized areas in Houston are sinking as much as 5 centimeters (2 inches) annually. Two other Texas cities, Fort Worth and Dallas, follow closely, while other fast-sinking spots include parts of New York's LaGuardia Airport, and sections of Las Vegas, Washington, D.C., and San Francisco.
The study also analyzed county-level groundwater extraction data, finding that this practice accounts for 80% of observed subsidence. Groundwater removal from aquifers, typically made up of fine-grained sediments, leads to land compaction and surface sinkage as the empty spaces once filled with water collapse. In Texas, oil and gas extraction further compounds the problem.
Natural forces also contribute to land subsidence in some regions. For instance, the weight of the massive ice sheet that once covered much of North America around 20,000 years ago caused the surrounding land to bulge upwards. Now, as the land slowly returns to equilibrium, cities like New York, Indianapolis, Nashville, Philadelphia, Denver, Chicago, and Portland are subsiding at rates of 1 to 3 millimeters annually.
The study identified eight major cities-New York, Chicago, Los Angeles, Phoenix, Houston, Philadelphia, San Antonio, and Dallas-that together account for over 60% of the people living in subsiding areas. These cities have experienced more than 90 significant floods since 2000, likely exacerbated by the ongoing land depression.
Another critical finding highlights differential motion within urban areas. In some cities, adjacent neighborhoods are sinking at different rates, or even rising in some cases, leading to potentially hazardous tilting of buildings. For example, while overall land in cities like Jacksonville, Fla., Memphis, Tenn., and San Jose, Calif., is subsiding, some areas within these cities are experiencing uplift, possibly due to rapid aquifer recharge near rivers.
While only about 1% of the total land area in the 28 studied cities is at risk of differential motion, these zones often include dense urban cores, with approximately 29,000 buildings potentially affected. The most vulnerable cities in this regard are San Antonio, where one in 45 buildings faces a high risk, followed by Austin (1 in 71), Fort Worth (1 in 143), and Memphis (1 in 167).
The authors urge cities to use this precise new data to implement targeted mitigation strategies, including enhanced drainage, land raising, and green infrastructure like artificial wetlands to reduce flood risks. Retrofitting existing structures and adjusting building codes for areas at high risk of differential motion could also reduce future infrastructure damage.
"As opposed to just saying it's a problem, we can respond, address, mitigate, adapt," said lead author Leonard Ohenhen, a postdoctoral researcher at the Columbia Climate School's Lamont-Doherty Earth Observatory. "We have to move to solutions."
Research Report:Quantifying Land Subsidence Impacts in US Metropolises
Related Links
Columbia Climate School
Climate Science News - Modeling, Mitigation Adaptation
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