by A number of coastal cities across the United States are “sinking” into the ground, according to new research, which could make problems related to sea level rise worse in the near future.
Much of the land in 32 coastal US cities could be at risk of flooding by 2050 due to subsidence, the gradual loss of land area or sinking, according to a paper published Wednesday in Nature.
The ongoing land loss will affect most coastal cities, said Leonard Ohenhen, Ph.D. candidate at Virginia Tech University specializing in coastal vulnerability and large-scale land subsidence, ABC News said.
Major cities surrounded by water — such as Boston, New Orleans and San Francisco — will be among the regions most likely to flood in the near future due to land elevation changes combined with sea level rise — about 4 millimeters per year, it is said. Ohenhen, who wrote the paper.
As many as 273,000 people and 171,000 properties could be affected in coastal regions across the US, according to the paper’s findings.
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The study found that coastal areas with higher elevation levels and lower subsidence rates, such as the Pacific Coast, have an overall lower flood threat.
For example, many parts of San Francisco’s hilly terrain won’t be a flood concern, but San Francisco International Airport and other parts of the city are on reclaimed land that drains into the surrounding bay, said Manoochehr Shirzaei, director of the Virginia Earth Observatory. Tech and Innovation Lab, said ABC News.
Conversely, areas with low elevation levels and higher subsidence rates, such as New Orleans and other areas along the Gulf Coast, were found to have a higher flood risk.
New Orleans, for example, is built on low-lying land within the sediments of the Mississippi River, causing the entire city to submerge at a rapid rate, said Shirzaei, who oversaw the research.
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Several surveyed locations on the Gulf Coast show significant levels of submergence — at rates equal to or greater than the current rate of global sea-level rise, Ohenhen said.
Biloxi, Mississippi, for example, is sinking about 5 millimeters a year, Ohenhen said.
The main driver of subsidence is groundwater extraction and sediment compaction, Shirzaei said.
Coastal subsidence is often underrepresented in flood models, the authors said. Inundation in coastal regions due to sea level rise may actually be worse than previously thought given how quickly the land is sinking, according to the study.
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However, land subsidence will be a key player in increasing flood hazards in the next three decades, Shirzaei said.
“What happens on the ground really affects us,” Ohenhen said. “And so if land is sinking on one side and you see it rising on the other side, you’re going to have areas that would be submerged in the future.”
Nearly 40% of the US population lives near the coast, according to the National Oceanic and Atmospheric Administration.
The sinking is expected to cause structural damage to most existing properties, Ohenhen said, adding that the paper does not even address the worst-case scenario in many regions.
“As climate change continues to worsen, we will see even worse consequences in most coastal cities,” he said.
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People living in coastal regions are already experiencing significant changes, Ohenhen said. In addition, the authors will particularly address disadvantaged communities, many of whom are already disproportionately struggling with the inequities of climate change, caused by subsidence and sea-level rise, the authors said.
Parts of low-lying Florida, such as Miami, are already dealing with “sunny day flooding” that occurs as a result of high tides. Miami showed the largest share of exposure to flooding, with up to 122,000 people and up to 81,000 properties potentially at risk of flooding by 2050, according to the paper.
Local management policies will need to be implemented to strengthen coastal infrastructure, as current hazard mitigation efforts are “inadequate,” the researchers said. Solutions include installing seawalls, raising existing properties above flood level and replenishing groundwater supplies, experts said.
“Land subsidence can be mitigated fairly quickly using engineering and nature-based solutions that we already have in our toolbox,” Shirzaei said.
US coastal cities are sinking as sea levels continue to rise, new research shows first on abcnews.go.com
