coastal cities

New Orleans is sinking

August 14, 2025 By EarthWise Leave a Comment

As climate change accelerates, rising sea levels are putting coastal communities at greater risk of flooding and storm surge. Driven by melting glaciers and warming oceans, global sea levels are rising at an increasing rate. For low-lying cities like New Orleans, even small increases can have serious consequences. And that risk is compounded by another factor: the land itself is sinking.

Much of New Orleans already sits at or below sea level, and parts of the city and its surrounding wetlands are gradually sinking. While most of the city remains stable, a new study by researchers from Tulane University suggests that sections of the region’s $15 billion post-Katrina flood protection system may require ongoing upgrades to keep pace with long-term subsidence.

The study, recently published in the journal Science Advances, used satellite data to track changes in ground elevation across Greater New Orleans between 2002-2020. The researchers found that some areas – including neighborhoods, wetlands, and even concrete floodwalls – are sinking by more than an inch each year. In some spots, the land is dropping by nearly two inches annually.

Alarmingly, some of the concrete floodwalls and levees built to protect the city after Hurricane Katrina are themselves sinking. In a few cases, they are losing elevation faster than sea levels are rising, reducing their capacity to block storm surges.

The study highlights how satellite monitoring can play a critical role in guiding infrastructure maintenance and urban planning – not just in New Orleans – but in vulnerable coastal cities around the world.

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Vertical land motion in Greater New Orleans: Insights into underlying drivers and impact to flood protection infrastructure

Photo, posted September 22, 2010, courtesy of U.S. Army Corps of Engineers via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Rising seas are destroying buildings

April 8, 2025 By EarthWise Leave a Comment

Alexandria is the second largest city in Egypt and is the largest city on the Mediterranean coast. Its history goes back over 2,300 years and it was once home to a lighthouse that was among the Seven Wonders of the Ancient World and a Great Library that was the largest in the ancient world. The modern city has more than 6 million residents but still has many historic buildings and ancient monuments. But perhaps not for long.

Rising seas and intensifying storms are taking a toll on the ancient port city. For centuries, Alexandria’s historic structures have endured earthquakes, storm surges, tsunamis, and more. They are truly marvels of resilient engineering. But now, climate change is undoing in decades what took millennia for humans to create.

Over the past two decades, the number of buildings collapsing in Alexandria has risen tenfold. Buildings are collapsing from the bottom up as a rising water table weakens soil and erodes foundations. Since 2001, Alexandria has seen 290 buildings collapse. Comparing present-day satellite imagery with decades-old maps, the authors of a study by the Technical University of Munich have tracked the retreat of Alexandria’s shorelines to determine where seas have intruded into groundwater. The authors say that more than 7,000 buildings in Alexandria are at risk. They call for building sand dunes and planting trees along the coast to block encroaching seawater.

The true cost of this gradual destruction goes far beyond bricks and mortar. This is the gradual disappearance of historic coastal cities. Alexandria is a warning for such cities around the world.

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In This Storied Egyptian City, Rising Seas are Causing Buildings to Crumble

Photo, posted September 11, 2012, courtesy of Sowr via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

New York Is Sinking | Earth Wise

June 29, 2023 By EarthWise Leave a Comment

The rising seas represent a threat to coastal cities across the globe. Increasing that threat is the fact that most global cities are slowly sinking as the earth beneath them settles and groundwater is removed. Another factor that has seldom been considered is that in major metropolises, the weight of large, concrete-and-steel skyscrapers may be hastening the sinking.

A new study by the U.S. Geological Survey published in the journal Earth’s Future estimated the weight of every building in New York City – 1.085 million of them – which they determined to add up to 1.68 trillion pounds – and estimated the downward force of those structures across the city.

The study found that buildings have a greater effect in areas that are rich in clay compared with those areas where sand or bedrock predominate. The softer the soil, the more compression there is from buildings. It wasn’t a mistake to build large buildings in New York, but it is important to understand that doing so pushes down the ground more and more.

The study determined that New York is sinking by around 1 to 2 millimeters each year, although some areas are sinking much faster. The researchers say that cities must plan for future sinking, which will exacerbate the impact of rising seas. Sea levels are rising 1 to 2 millimeter each year, so the subsidence caused by the weight of buildings is equivalent to moving a year ahead in time with regard to rising ocean levels. This is not a cause for immediate panic, but it is important to understand that this ongoing process only increases the risk of inundation from flooding.

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New York City Sinking Under Weight of Skyscrapers

Photo, posted January 29, 2016, courtesy of Always Shooting via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Sinking Cities | Earth Wise

October 24, 2022 By EarthWise Leave a Comment

Sea levels across the globe are rising as a result of the changing climate. Two factors are largely responsible: the melting of ice sheets in the polar regions and the fact that as the oceans get warmer, the water in them expands.

Estimates are that by 2050, there will be over 800 million people living in 570 cities that will be at risk from rising sea levels. The rising waters can drown neighborhoods, put people’s lives at risk, and wreck entire economies. Unless global emissions can be reduced sufficiently, sea levels will continue to rise.

A new study, published in the journal Nature Sustainability by Nanyang Technical University in Singapore in collaboration with the University of New Mexico, ETH Zurich, and NASA’s Jet Propulsion Lab, has focused on yet another aspect of the threat to coastal cities. They have found that many densely populated coastal cities worldwide are even more vulnerable to sea level rise because much of their land is sinking.

The researchers processed satellite images of 48 cities from 2014 to 2020 using a system called Interferometric Synthetic Aperture Radar. They found that land subsidence varied on a neighborhood and even individual block level but across all the cities studied, there was a median sinking speed of 6/10” a year. Some places had land that is sinking at 1.7” per year. Meanwhile, the global mean sea-level rise is about .15” per year.

The increasing prevalence of industrial processes such as the extraction of groundwater, and oil and gas, along with the rapid construction of buildings and other urban infrastructure are leading to the sinking of the urban areas.

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Rapid land sinking leaves global cities vulnerable to rising seas

Photo, posted October 24, 2015, courtesy of Jeffrey via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Keeping Charleston Dry | Earth Wise

June 11, 2020 By EarthWise Leave a Comment

Charleston, South Carolina is visited by millions of tourists each year. The town is a glimpse into the past, showcasing antebellum mansions, row houses, historic African American churches and scenic harbor views from a Civil War-era promenade.

Charleston is also visited more and more by water from rising seas and increasingly powerful storms. The city is essentially drowning in slow motion and may soon face an existential threat to its survival.

Charleston has a harbor and three rivers and water from all these sources leaks in at every bend and curve, fills streets, disrupts businesses, and rushes into homes during storms. Million-dollar antebellum mansions, built on spongy marsh and old tidal creeks, flood repeatedly.

City officials have endorsed a plan by the U.S. Army Corps of Engineers to wall off the historic downtown with an 8-mile-long seawall that would cost nearly $2 billion. The proposed barricade is just one of many proposed projects to build seawalls, surge gates, levees, and other barriers to defend U.S. coastal cities in an era of rising seas and climate-fueled floods and storms. A proposed flood wall in Miami would cost federal taxpayers $8 billion.

Researchers generally agree that sea levels are likely to rise by at least 3 feet by the end of the century. Some experts believe the rise will be much greater. So, a key question is whether these barriers will actually keep out the water. Critics of many of the proposed solutions contend that they are doomed to fail.

Flooding has caused nearly $1 trillion worth of damage along the East and Gulf coasts over the past 40 years. And things are almost certain to get worse in Charleston and other coastal cities.

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Fortress Charleston: Will Walling Off the City Hold Back the Waters?

Photo, posted October 7, 2015, courtesy of Jeff Turner via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.