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Scientific American
08-05-2025
- Science
- Scientific American
The 28 Most Populous Cities in the U.S. Are All Sinking
All 28 of the most populous cities in the U.S. are sinking, worsening risks of flooding and damage to urban infrastructure, a new study finds. One of the main culprits is the extraction of groundwater to quench the thirst of growing populations and commerce. The research, published Thursday in Nature Cities, shows this subsidence is 'ubiquitous—people should be looking everywhere' for it, says Cornell University geophysicist Matt Pritchard, who was not involved with the study. People have long known that certain cities around the world are sinking, particularly coastal ones. In the U.S., New Orleans has been perhaps the most famous example. This subsidence can have both natural and humanmade causes, such as ground that continues to respond to the retreat of the ice sheets, dams that prevent sediment from replenishing river deltas and buildings that weigh a city down. On supporting science journalism If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today. A few detailed studies have been conducted on some particular cities, such as Miami, but otherwise data have come from sparse, on-the-ground measurements that don't reveal the nuance needed to properly gauge risks to infrastructure. To get granular data, the researchers behind the new study turned to interferometric synthetic aperture radar (InSAR) measurements taken from satellites. Study co-author Leonard Ohenhen, a postdoctoral researcher at Columbia University's Lamont-Doherty Earth Observatory, explains that InSAR is akin to bouncing a ball at a steady rate against a wall. If the wall moves away from you, the ball takes longer to bounce back. If the wall moves closer, the ball returns more quickly. Similarly, in the new research, the pulses sent out by the InSAR device were able to detect upward and downward deformations of Earth's surface down to the millimeter scale in grids made up of 28-meter squares. The team found that in all 28 cities examined in the study—which each have populations of more than 600,000—at least 20 percent of their area was sinking. In 25 of them, at least 65 percent was subsiding. Nine cities—New York City, Chicago, Houston, Dallas, Fort Worth, Columbus, Seattle, Denver and Detroit—had an area-weighted average rate of subsidence of more than two millimeters per year. Houston, Fort Worth and Dallas had the highest rates of any of the cities, with an average of more than 4 mm per year. In fact, more than 42 percent of Houston is sinking faster than 5 mm per year, and 12 percent is sinking by more than 10 mm per year. Those numbers may sound small, but measurements began around 2015, meaning 'it's been 10 years at that rate—and that starts to add up,' Pritchard says. Also, damage can occur even with small displacements. 'The value here is in detecting things before they get worse or at smaller more subtle scales,' he adds. This is particularly true when there are different rates of sinking across a city, or even areas where some ground is sinking and some is rising. The study showed how ground deformation varied across the cities—for example, the area around LaGuardia Airport is sinking much faster than most of the rest of New York City. These different rates can cause buildings to tilt and can lead to other infrastructure damage. 'We have buildings that collapse from this type of ground deformation,' Pritchard says, citing conditions that might have played a role in the 2021 collapse of a condominium in the Miami suburb of Surfside, Fla. Of the 5.6 million buildings in the cities examined in the study, about 29,000 are in areas of concern. That doesn't mean those buildings will necessarily be damaged; factors such as soil type, construction methods and building age can come into play. But it does show where a more detailed analysis should be done, Pritchard and Ohenhen say. Another subsidence-related concern is flooding. When you have areas of sinking in a city, it can create a 'subsidence bowl,' Ohenhen says. 'Where the land was flat, [water] could easily flow from one place to the other,' but now it gets trapped in that bowl instead. The reasons for the subsidence vary from city to city, and even within a city, but the team found that 80 percent of the sinking was associated with groundwater extraction. That points to the need to balance demand for water with maintaining aquifers to avoid collapse. Cities in drought-prone regions, such as Texas, should be particularly concerned because when drought sets in, 'you a have a really, really high probability' of further subsidence as aquifers become more depleted, Ohenhen says. Pritchard says the study shows that subsidence is a problem outside of previous poster cities such as New Orleans—and that 'we really we should be looking at this everywhere, not even just in large cities.'
Yahoo
08-05-2025
- Science
- Yahoo
28 big American cities are sinking
It's not unknown that some major urban areas in the United States are sinking. And the problem could be even more widespread. A new analysis of the 28 most populated cities in the country found that all of them are sinking by roughly two to 10 millimeters (about 0.07 to 0.39 inches) per year. The major cause? Groundwater extraction as the demand for freshwater grows. The findings are detailed in a study published May 8 in the journal Nature Cities. While land sinking less than an inch per year might not seem like much on paper, small shifts in land can have big effects. Land shifts downward can impact the structural integrity of buildings, roads, bridges, and dams. A 2024 study found that regions of the Atlantic coast to be sinking by as much as five millimeters per year. This new study used satellite-based radar measurements to create high-res maps of subsidence–or sinking land– in these areas. They looked at the subsidence for the 28 most populated cities in the US–including New York, Dallas, and Seattle–which are home to 34 million people or roughly 12 percent of the US population. 'What makes this work especially powerful is the use of satellite radar (InSAR) to map subsidence in incredible detail,' study co-author and Virginia Tech geodesist/geophysicist Manoochehr Shirzaei tells Popular Science. 'Think of it like getting a CAT scan of the Earth's surface—except from space. This technology helps city planners and engineers pinpoint exactly where the ground is moving, which is essential for proactive maintenance, zoning, and flood risk planning.' In all of the cities studied, at least 20 percent of the urban area is sinking. In 25 out of the 28, at least 65 percent is sinking. New York, Chicago, Seattle, Denver, Columbus, Dallas, Forth Worth, and Houston are sinking at roughly two millimeters per year. Additionally, several cities in Texas showed some of the highest measured rates of subsidence at about 5 millimeters per year. Certain parts of Houston are seeing as much as 10 millimeters per year, according to the study. [ Related: NYC is sinking and climate change is only making it worse. ] 'A lot of small changes will build up over time, magnifying weak spots within urban systems and heighten flood risks,' Leonard Ohenhen, the study's lead author and a postdoctoral research scientist at Lamont-Doherty Earth Observatory at Columbia University, said in a statement. This evidence from Houston shows some differences in sinking rates between localized zones and areas right next door. This shows one of the more harmful and somewhat invisible effects of subsidence. With something like flood hazards, the risks are visible only when the land sinks below a specific threshold. However, inconsistent land motion–like what researchers observed in Houston–can crack and destabilize buildings, foundations, and infrastructure. When the team assessed how infrastructure risks increase when subsidence rates vary, they found that New York, Las Vegas, and Washington, DC. also had high rates of variance. The slow nature also means that its infrastructure quality can be quietly compromised over time, according to Shirzaei. 'Several telltale signs of land subsidence are visible to the naked eye and may indicate early stages of ground sinking or differential settlement,' he says. 'In urban areas, these signs often appear gradually but can become serious if left unaddressed, especially in cities built on soft soils or where groundwater is heavily extracted.' Shirzaei says that some of these telltale signs include: Cracks in buildings, especially around doors, windows, and foundations, uneven or sloping floors inside homes or buildings. Misaligned doors and windows that no longer close properly. Warped roads or buckling pavements, often misattributed to poor construction. Tilting utility poles or fences, which can be an indicator of shifting ground. Increased local flooding, especially during normal rain events, as land sinks and alters drainage patterns. Continued urban sprawl and population growth only increases the demand for freshwater. If water is taken out of an underground aquifer faster than it can be replenished, the aquifer itself can crumble and compact in the ground. 'One of the key takeaways from our study is that land subsidence is not just a coastal problem or something happening far away—it's occurring in many of America's cities and affecting millions of people,' Shirzai says. 'More than 34 million urban residents live on sinking ground, and over 29,000 buildings are in high-risk zones. Subsidence often occurs slowly—millimeters per year—but its effects accumulate and can silently undermine infrastructure like roads, bridges, and homes.' The compounding effects of shifts in weather patterns with continued urban population and socioeconomic growth are also possibly accelerating the rate of land sink. Previously stable urban areas could be transformed into vulnerable zones for flooding, infrastructure failure, and long-term land degradation. Based on the data from this study, the team suggests that cities integrate land subsidence monitoring into urban planning policies to keep risks from getting worse. They also recommend targeted strategies including managing groundwater to reduce excessive withdrawals and long-term monitoring to facilitate early action. 'There's a hopeful message: subsidence is a solvable problem,' says Shirzaei. 'Much of it is caused by human actions, especially overuse of groundwater. With better monitoring, smarter urban development, and policies that address water use and infrastructure resilience, we can slow or even stop the sinking—and protect our cities for future generations.'
Yahoo
05-05-2025
- Science
- Yahoo
13 coastal cities in the US that are slowly sinking
Cities all over the world, including on the US East and Gulf Coasts, are sinking. This phenomenon, called subsidence, can make extreme flooding worse and damage infrastructure. From New York to Houston, these 13 cities are losing height each year. Cities are sinking across the US, some at a few fractions of a millimeter each year, while others lose up to six millimeters a year. This phenomenon, called subsidence, is a "slow-moving yet widespread hazard," said Manoochehr Shirzaei, a geophysicist at Virginia Tech who co-authored a study published in Nature in March that measured subsidence in 32 coastal cities in the US. Sinking can come from the sheer weight of skyscrapers and infrastructure, or from people drawing water from underground. Some of it is leftover from the last Ice Age. Coastal cities worldwide are already prone to catastrophic flooding as sea levels rise because of the climate crisis. Factor in sinking, and the world's vulnerability to future coastal flooding triples, according to a 2019 study. In the US, sea-level rise combined with subsidence could expose $109 billion of coastal property to high-tide flooding by 2050, according to Shirzaei's calculations. The good news is that there are relatively inexpensive solutions to subsidence, Shirzaei told Business Insider in an email. "The key takeaway is that we still have sufficient time to manage this hazard," he said. Here are the biggest cities that are sinking the most, according to his new study, in geographical order starting from the northern East Coast. Boston, Massachusetts Shirzaei and his co-authors have found that there's a lot of variation in subsidence throughout Boston. When sinking occurs at different rates like that, it can put extra strain on infrastructure. For example, some areas of Boston are sinking about 1 millimeter per year, give or take. Others sink nearly 4 millimeters a year — which translates to almost 4 centimeters per decade. New York City The Big Apple is losing about 1.5 millimeters of height each year. All three airports in the NYC area are sinking, too, according to a study Shirzaei co-authored in 2024. JFK is sinking about 1.7 mm per year, LaGuardia at 1.5 mm per year, and Newark's airport is clocking 1.4 mm per year. LaGuardia, for one, has already installed water pumps, berms, flood walls, and flood doors. Previous estimates had Laguardia flooding monthly by 2050 and fully underwater by 2100 — and that's without subsidence. Jersey City, New Jersey Just across the Hudson River, Jersey City is matching NYC's pace of about 1.5 millimeters per year. To measure sinking at such a granular level, Shirzaei and his co-authors mapped ground deformations using a satellite-based radar technique called InSAR (short for Interferometric Synthetic Aperture Radar). Atlantic City, New Jersey A little further south, Atlantic City has its neighbors beat with a subsidence of about 2.8 millimeters per year. A portion of the East Coast's subsidence is a leftover reaction from the disappearance of the Laurentide ice sheet, which covered much of North America during the last Ice Age. The ice sheet's bulk caused the exposed land around its edges to bulge upward — and the mid-Atlantic region is still settling down from the ice sheet's retreat. Virginia Beach, Virginia Virginia Beach, Virginia, is sinking 2.2 millimeters per year. Meanwhile, sea level rise has become a growing concern for locals. In 2021, residents voted in favor of a $568 million program to build infrastructure that guards against rising sea level, according to PBS news. Charleston, South Carolina Charleston is the most populous city in South Carolina and its downtown sits on a peninsula flanked by the Ashley River and Cooper River. The city overall is sinking at a median rate of 2.2 millimeters per year, though in some areas its more dramatic at a rate of 6 millimeters per year. Savannah, Georgia Savannah is losing almost 2 millimeters per year, though some areas are sinking as much as 5 millimeters per year. Over 13,000 properties in Savannah are at risk of flooding over the next 30 years, according to the climate risk analysis group First Street. That's over 23% of all homes in the city. Miami Last year, a study found that luxury high-rises were slowly sinking on the barrier islands surrounding Miami, possibly due to vibration from nearby construction. Shirzaei found the mainland is sinking, too, by about half a millimeter each year. Mobile, Alabama Mobile is losing 1.87 millimeters per year. The Gulf Coast city experiences some of the highest volume of rain in the US, according to the city's official website, and encourages all residents to have disaster survival kits, including canned foods and flashlights, on hand in the event of a flooding emergency. Biloxi, Mississippi Biloxi has the most drastic subsidence of all the US cities Shirzaei's team assessed. On the whole, Biloxi is sinking about 5.6 millimeters per year, with a lot of variation. Some parts of the city may be sinking as much as 10 millimeters per year. New Orleans New Orleans is losing 1.3 millimeters per year. First Street reports that 99.6% of all properties in the city are at risk of flooding in the next 30 years. Houston and Galveston, Texas Shirzaei found that Galveston, Texas, is sinking more than 4 millimeters a year, but inland parts of Houston have also been sinking for decades due to groundwater extraction. Corpus Christi, Texas Corpus Christi is sinking almost 3 millimeters per year. Some researchers think local oil and gas drilling has contributed to subsidence, reported local ABC outlet KIIV "Extraction, generally, we believe it initiates and activates movement around faults and those could initiate land subsidence in some areas," Mohamed Ahmed, a geophysics professor at Texas A&M-Corpus Christi, told the outlet. What about the West Coast? Shirzaei's team didn't find much subsidence in California's coastal cities, although the state's inland Central Valley is sinking due to groundwater extraction. As for Oregon and Washington, the researchers simply don't have good enough data yet to say what's happening to the ground there. Read the original article on Business Insider
Business Insider
05-05-2025
- Science
- Business Insider
13 coastal cities in the US that are slowly sinking
Boston, Massachusetts Shirzaei and his co-authors have found that there's a lot of variation in subsidence throughout Boston. When sinking occurs at different rates like that, it can put extra strain on infrastructure. For example, some areas of Boston are sinking about 1 millimeter per year, give or take. Others sink nearly 4 millimeters a year — which translates to almost 4 centimeters per decade. New York City The Big Apple is losing about 1.5 millimeters of height each year. All three airports in the NYC area are sinking, too, according to a study Shirzaei co-authored in 2024. JFK is sinking about 1.7 mm per year, LaGuardia at 1.5 mm per year, and Newark's airport is clocking 1.4 mm per year. LaGuardia, for one, has already installed water pumps, berms, flood walls, and flood doors. Previous estimates had Laguardia flooding monthly by 2050 and fully underwater by 2100 — and that's without subsidence. Jersey City, New Jersey Just across the Hudson River, Jersey City is matching NYC's pace of about 1.5 millimeters per year. To measure sinking at such a granular level, Shirzaei and his co-authors mapped ground deformations using a satellite-based radar technique called InSAR (short for Interferometric Synthetic Aperture Radar). Atlantic City, New Jersey A little further south, Atlantic City has its neighbors beat with a subsidence of about 2.8 millimeters per year. A portion of the East Coast's subsidence is a leftover reaction from the disappearance of the Laurentide ice sheet, which covered much of North America during the last Ice Age. The ice sheet's bulk caused the exposed land around its edges to bulge upward — and the mid-Atlantic region is still settling down from the ice sheet's retreat. Virginia Beach, Virginia Virginia Beach, Virginia, is sinking 2.2 millimeters per year. Meanwhile, sea level rise has become a growing concern for locals. In 2021, residents voted in favor of a $568 million program to build infrastructure that guards against rising sea level, according to PBS news. Charleston, South Carolina Charleston is the most populous city in South Carolina and its downtown sits on a peninsula flanked by the Ashley River and Cooper River. The city overall is sinking at a median rate of 2.2 millimeters per year, though in some areas its more dramatic at a rate of 6 millimeters per year. Savannah, Georgia Savannah is losing almost 2 millimeters per year, though some areas are sinking as much as 5 millimeters per year. Over 13,000 properties in Savannah are at risk of flooding over the next 30 years, according to the climate risk analysis group First Street. That's over 23% of all homes in the city. Miami Last year, a study found that luxury high-rises were slowly sinking on the barrier islands surrounding Miami, possibly due to vibration from nearby construction. Shirzaei found the mainland is sinking, too, by about half a millimeter each year. Mobile, Alabama Mobile is losing 1.87 millimeters per year. The Gulf Coast city experiences some of the highest volume of rain in the US, according to the city's official website, and encourages all residents to have disaster survival kits, including canned foods and flashlights, on hand in the event of a flooding emergency. Biloxi, Mississippi Biloxi has the most drastic subsidence of all the US cities Shirzaei's team assessed. On the whole, Biloxi is sinking about 5.6 millimeters per year, with a lot of variation. Some parts of the city may be sinking as much as 10 millimeters per year. New Orleans New Orleans is losing 1.3 millimeters per year. First Street reports that 99.6% of all properties in the city are at risk of flooding in the next 30 years. Houston and Galveston, Texas Shirzaei found that Galveston, Texas, is sinking more than 4 millimeters a year, but inland parts of Houston have also been sinking for decades due to groundwater extraction. Corpus Christi, Texas Corpus Christi is sinking almost 3 millimeters per year. Some researchers think local oil and gas drilling has contributed to subsidence, reported local ABC outlet KIIV "Extraction, generally, we believe it initiates and activates movement around faults and those could initiate land subsidence in some areas," Mohamed Ahmed, a geophysics professor at Texas A&M-Corpus Christi, told the outlet. What about the West Coast? Shirzaei's team didn't find much subsidence in California's coastal cities, although the state's inland Central Valley is sinking due to groundwater extraction. As for Oregon and Washington, the researchers simply don't have good enough data yet to say what's happening to the ground there.
Forbes
16-04-2025
- Science
- Forbes
New Zealand's Major Cities Are Sinking
Global mean sea level has risen about 21-24 centimeters (8-9 inches) since 1880. Staggeringly, somewhere around 10 cm of that rise has happened in the past 30 years, and the rate at which sea levels are rising is accelerating – it was ~2.1 mm/year in 1993, and now it's ~4.5 mm/year. For coastal populations, of which there are a lot – close to 1 billion people (or ~12.5% of the world's population) live within 10 km of a coastline – sea level rise isn't some far off threat. Its impacts are already being felt. Storm surges during Hurricane Helene brought devastation to coastal communities across the Southeast US in 2024. Cities including NYC, and Panjin in China are increasingly experiencing floods at high tide, even in times of good weather. No coastal city is immune to the impacts of sea-level rise. And as a new study from a group of New Zealand researchers shows, human activity is exacerbating the risk. Their analysis found that in many NZ cities, shorelines are steadily subsiding or sinking, which means that rising seas will affect them sooner. Global sea level rise is largely driven by two factors, that in turn are a result of our warming climate. The first (and largest) contributor is the melting of ice sheets and glaciers, particularly in the polar regions. The Greenland ice sheet alone is estimated to be shedding about 270 billion tons of ice per year. The second driver is the thermal expansion of the ocean. Water, like all liquids, expand when they're heated. And more than 90% of the heat trapped in our atmosphere – thanks to an accumulation of greenhouse gases – is eventually absorbed by our oceans. A warmer ocean takes up more space than a cooler one, and so we're seeing higher sea levels. This effect is estimated to cause roughly one-third of the global sea-level rise observed by satellites since 2004. However, there are other causes that are far more localized. The land itself may be sinking (or lifting), either as a result of tectonic activity, or of human activity – namely, groundwater extraction, dredging, and land reclamation. These activities can 'potentially double or triple the effects of sea-level rise in certain places,' writes Dr Jesse Kearse, a Postdoctoral Researcher at Kyoto University. Here in Aotearoa NZ, the effects of these land changes on urban areas have been examined in detail for the first time. The results paint a rather worrying picture for our coastal infrastructure. Kearse is the lead author of this new paper, and an expert on measuring vertical land motion using a satellite-based mapping technique called InSAR (Interferometric Synthetic Aperture Radar). 'InSAR allows us to map ground deformation using radar images of the earth's surface,' he explains, speaking over Zoom from Japan. 'It's an active source imaging system – it's not about passively collecting reflected light like you do for optical images. The radar signal is beamed down from a satellite, it hits the surface and reflects back.' The radar satellite used by Kearse and his colleagues is called Sentinel-1. For the past decade, it has been continuously collecting radar imagery of our planet, and making it available via the European Space Agency's database. It's been used to monitor everything from marine winds to soil moisture, and for emergency responses. Unlike optical satellites, SAR can see through clouds and operate both day and night. Captured within a radar image are two pieces of information: amplitude and phase. You can think of the amplitude as the strength of the return signal – it is influenced by the physical properties of the surface. But if you're interested in measuring ground deformation, phase is the useful part. Radar waves have a specific wavelength, 'around five centimeters' in the case of Sentinel-1, so the distance from the satellite to the ground and back again can be expressed in terms of that wavelength (distance = some number of full wavelengths plus some fraction of a wavelength). When you compare two images of the same area taken on different dates, anywhere that you find extra or fewer fractions of a wavelength (i.e. a change in phase) will likely be a spot where the ground has changed its vertical position between those images – it may have subsided or lifted, relative to the ground around it. Phase differences can be measured with very high accuracy. To turn those relative measurements of vertical motion into true or absolute measurements, you need to use a reference – ideally sensors on the ground within the same area that can also measure small ground movements. New Zealand already has a network of suitable sensors. Called GeoNet, it acts as a geological hazard monitoring system, and it continuously collects ground deformation data from its GNSS stations around the country. The combination of high-resolution InSAR data and GeoNet's GNSS data allowed Kearse and his colleagues to measure vertical land movement between 2018 and 2021 at major urban coastal strips around the country; namely, Auckland, Tauranga, Wellington, Christchurch, and Dunedin. Together, these areas are home to the majority of the population. 'One of our main conclusions was that the coastal strip is going down consistently in all of these cities, and it's happening at a rate of a few millimeters each year,' Kearse says. In terms of numbers, they found that 77% of NZ's urban coastlines are subsiding at rates of 0.5 mm/yr or more. Some of the fastest subsidence rates – more than 3.0 mm/yr – were measured in the coastal suburbs of Christchurch. They also identified highly-localized hotspots, with subsidence rates exceeding 15 mm/yr in some cases. 'These human-modified parts of the coastline are going down at locally much faster rates than the rest of the coast, which in turn is going down faster than the inland areas,' he says. While the researchers didn't delve into the cause of these subsidence hotspots in this paper, Kearse has noticed a pattern. 'There's a lot of reclaimed land in New Zealand cities – some of it you cannot detect, and some stands out really clearly in the images. I'm not an engineer, but the methodology or the engineering approach that was used to reclaim the land seems to have a significant effect on its current stability.' In the interview, he gives the example of Wellington Airport whose construction required the movement of 'three million cubic meters of earth and rock', as well as significant land reclamation. 'That was a huge engineering effort. A lot of research, a lot of care and attention was paid to that construction,' says Kearse, 'and it remains very stable. But then you have areas like Naval Point [in Christchurch] Many of the subsiding areas are home to heavy industries, ports and other critical infrastructure like wastewater treatment plants. When asked how worried the public should be about this in the coming decades, Kearse says, 'I think that's a bit outside of my expertise, but my personal opinion is that there are still a lot of unanswered questions in terms of what's actually going on. Are these subsidence rates going to persist for decades to centuries? It's not clear.' Something that complicates the picture is the fact that New Zealand is one of the most seismically-active areas on the planet. It straddles the boundary of two tectonic plates – the Pacific plate and the Australian plate. At the bottom of the South Island (Te Waipounamu), the Australian Plate dives, or subducts, below the Pacific plate. Just off the east coast of the North Island (Te Ika-a-Māui), the situation is reversed – there, the Pacific plate plunges below the Australian one. Wellington's location along the plate boundary means that it can experience large, sudden quakes as well as 'slow-slip events', where faults can move over a period of weeks or months. This complexity is 'really problematic for trying to understand long-term vertical land motion in the capital city,' says Kearse 'In inter-slow-slip time periods, the whole subduction system pulls Wellington down by about 3 mm a year. And then for a few months that will rebound and it might regain 50 or 60% of that accumulated subsidence. And then the cycle will repeat again.' Kearse says that he found no evidence of land subsidence accelerating in recent years – 'in most cases, it was either pretty steady or even decelerating' – but he reemphasized the paper's conclusions, saying 'Vertical land motion has to be considered in any assessment of sea level rise, and in any future development plans for those vulnerable urban areas.'
