The Land Beneath the Biggest U.S. Cities Is Sinking, Finds New Analysis of Satellite Data
The Land Beneath the Biggest U.S. Cities Is Sinking, Finds New Analysis of Satellite Data
Largely due to groundwater pumping and shifting of land after the last ice age, major urban areas are subsiding, which could destabilize buildings or worsen flooding
Houston is the fastest-sinking of the 28 most populated U.S. cities, according to a new study that examined the urban areas through satellite observations. The Texas city got most of its water from the ground in the 1950s to ’70s, which led to subsidence.
Art Wager via Getty Images
The 28 most populous cities in the United States are all sinking to some degree, according to a new study that highlights the vulnerability of the roads and buildings in metropolises like New York, Houston and Seattle.
In 25 of those 28 cities, at least two-thirds of the land area is sinking, per the research, and most of that subsidence is caused by pumping groundwater. The team’s findings were published in the journal Nature Cities last week.
“As cities continue to grow, we will see more cities expand into subsiding regions,” says Leonard Ohenhen, the study’s lead author and a researcher at Columbia University, in a statement. “Over time, this subsidence can produce stresses on infrastructure that will go past their safety limit.”
The researchers used satellite data collected between 2015 and 2021 to determine the rising and falling of land across major cities. “By comparing multiple images taken over time from the same area, we can detect tiny vertical movements of the ground, down to a few millimeters per year,” explains Manoochehr Shirzaei, a study co-author and geophysicist at Virginia Tech, to James Woodford at New Scientist. “It’s like taking a high-resolution time-lapse of Earth’s surface and watching how it rises or sinks over time.”
Across the country, 80 percent of the sinkage is associated with removing groundwater for drinking and agriculture—and the researchers don’t see the problem getting better in the near future.
“The usage of groundwater is not going to decline,” Ohenhen tells Kasha Patel and Naema Ahmed at the Washington Post. “In most places, you are not going to tell people to stop extracting groundwater, because that may be the only available resource for a particular region or city.”
Researchers pinpointed the rate of sinking across major U.S. cities. This map shows the level of vertical land motion in the nation's most populated urban areas.
Columbia Climate School
Houston is the fastest-sinking city the team studied, largely for that reason—in the 1950s to ’70s, nearly all of its water came from the ground, says Bob Wang, a geophysicist at the University of Houston, to the New York Times’ Mira Rojanasakul. And while mitigation efforts slowed subsidence in the city’s center, people continued to pump water from below as the urban area expanded. Now, 42 percent of Houston’s land area is sinking faster than five millimetersper year, and 12 percent of it is sinking faster than ten millimetersper year.
For other cities along the East Coast and Great Lakes area, such as New York, Philadelphia and Washington, D.C., the sinking primarily comes as the land slowly settles after the melting of glaciers from the last ice age. This phenomenon, which makes the ground rise in some areas and sink in others, is called glacial isostatic adjustment.
“During the last ice age, these areas were covered by massive ice sheets. The sheer weight of the ice pushed down on Earth’s crust, like sitting on a memory foam mattress,” explains Shirzaei to New Scientist.
When the ice melted, the pressure on the Earth’s surface was lifted, and the crust that was beneath it started to rise. But this rebound isn’t happening evenly across all regions, adds Shirzaei. In some areas, “the land is still sinking rather than rising, because they’re near the forebulge,” he says to New Scientist, “a zone that had been pushed up by the weight of the ice nearby and is now collapsing.”
Shifting land—especially if it happens unevenly—can lead to destabilized structures and flooding hazards. Because of those risks, the team hopes their study creates a push toward damage mitigation efforts, per the statement. In cities susceptible to tilting, that can look like retrofitting existing buildings, implementing new building codes and limiting construction in the most vulnerable areas. To help with flooding, municipalities can implement land raising, enhance their draining systems and build more green infrastructure, like artificial wetlands.
“Having detailed maps of ground movement as well as the information of what causes it can aid in designing policies,” says Pejman Tahmasebi, a subsidence researcher at the Colorado School of Mines who was not involved in the study, to the Washington Post.
“We should start talking about those solutions right now,” adds Ohenhen to the Washington Post. “This problem is always only going to increase as we progress into the future.”
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#land #beneath #biggest #cities #sinking
The Land Beneath the Biggest U.S. Cities Is Sinking, Finds New Analysis of Satellite Data
The Land Beneath the Biggest U.S. Cities Is Sinking, Finds New Analysis of Satellite Data
Largely due to groundwater pumping and shifting of land after the last ice age, major urban areas are subsiding, which could destabilize buildings or worsen flooding
Houston is the fastest-sinking of the 28 most populated U.S. cities, according to a new study that examined the urban areas through satellite observations. The Texas city got most of its water from the ground in the 1950s to ’70s, which led to subsidence.
Art Wager via Getty Images
The 28 most populous cities in the United States are all sinking to some degree, according to a new study that highlights the vulnerability of the roads and buildings in metropolises like New York, Houston and Seattle.
In 25 of those 28 cities, at least two-thirds of the land area is sinking, per the research, and most of that subsidence is caused by pumping groundwater. The team’s findings were published in the journal Nature Cities last week.
“As cities continue to grow, we will see more cities expand into subsiding regions,” says Leonard Ohenhen, the study’s lead author and a researcher at Columbia University, in a statement. “Over time, this subsidence can produce stresses on infrastructure that will go past their safety limit.”
The researchers used satellite data collected between 2015 and 2021 to determine the rising and falling of land across major cities. “By comparing multiple images taken over time from the same area, we can detect tiny vertical movements of the ground, down to a few millimeters per year,” explains Manoochehr Shirzaei, a study co-author and geophysicist at Virginia Tech, to James Woodford at New Scientist. “It’s like taking a high-resolution time-lapse of Earth’s surface and watching how it rises or sinks over time.”
Across the country, 80 percent of the sinkage is associated with removing groundwater for drinking and agriculture—and the researchers don’t see the problem getting better in the near future.
“The usage of groundwater is not going to decline,” Ohenhen tells Kasha Patel and Naema Ahmed at the Washington Post. “In most places, you are not going to tell people to stop extracting groundwater, because that may be the only available resource for a particular region or city.”
Researchers pinpointed the rate of sinking across major U.S. cities. This map shows the level of vertical land motion in the nation's most populated urban areas.
Columbia Climate School
Houston is the fastest-sinking city the team studied, largely for that reason—in the 1950s to ’70s, nearly all of its water came from the ground, says Bob Wang, a geophysicist at the University of Houston, to the New York Times’ Mira Rojanasakul. And while mitigation efforts slowed subsidence in the city’s center, people continued to pump water from below as the urban area expanded. Now, 42 percent of Houston’s land area is sinking faster than five millimetersper year, and 12 percent of it is sinking faster than ten millimetersper year.
For other cities along the East Coast and Great Lakes area, such as New York, Philadelphia and Washington, D.C., the sinking primarily comes as the land slowly settles after the melting of glaciers from the last ice age. This phenomenon, which makes the ground rise in some areas and sink in others, is called glacial isostatic adjustment.
“During the last ice age, these areas were covered by massive ice sheets. The sheer weight of the ice pushed down on Earth’s crust, like sitting on a memory foam mattress,” explains Shirzaei to New Scientist.
When the ice melted, the pressure on the Earth’s surface was lifted, and the crust that was beneath it started to rise. But this rebound isn’t happening evenly across all regions, adds Shirzaei. In some areas, “the land is still sinking rather than rising, because they’re near the forebulge,” he says to New Scientist, “a zone that had been pushed up by the weight of the ice nearby and is now collapsing.”
Shifting land—especially if it happens unevenly—can lead to destabilized structures and flooding hazards. Because of those risks, the team hopes their study creates a push toward damage mitigation efforts, per the statement. In cities susceptible to tilting, that can look like retrofitting existing buildings, implementing new building codes and limiting construction in the most vulnerable areas. To help with flooding, municipalities can implement land raising, enhance their draining systems and build more green infrastructure, like artificial wetlands.
“Having detailed maps of ground movement as well as the information of what causes it can aid in designing policies,” says Pejman Tahmasebi, a subsidence researcher at the Colorado School of Mines who was not involved in the study, to the Washington Post.
“We should start talking about those solutions right now,” adds Ohenhen to the Washington Post. “This problem is always only going to increase as we progress into the future.”
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#land #beneath #biggest #cities #sinking
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