Dozens of cities along the US coastline are sinking at alarming rates, leaving them far more exposed to devastating flooding from sea level rise than previously thought, scientists reported Wednesday.
As oceans rise and the coasts sink, up to 343,000 acres of land will be exposed to destructive flooding by 2050, from hazards such as hurricanes, coastal storms and shoreline erosion, according to the study published in the journal Nature. In a worst-case scenario, roughly 1 in 50 people in the 32 cities analyzed could be exposed to flood threats.
According to the researchers, this is the first study to combine the increasing threat of sea level rise with high-resolution measurements of sinking areas to determine which coastal locations are most at-risk of inundation. “Every single result of this research is novel,” said Manoochehr Shirzaei, a geophysicist at Virginia Tech and co-author of the study.
The impact of sinking land has been overlooked, said Leonard Ohenhen, the lead author of the study and a doctoral researcher at Virginia Tech. “When you have these two different processes laid out — land sinking on the coast and sea rising on the ocean — you’re going to have a lot more areas that will be susceptible to flooding in the future,” he told CNN.
Cities on the East Coast where sinking land is exacerbating sea level rise include New York City and Atlantic City; Virginia Beach; Charleston, South Carolina; and Savannah, Georgia.
Many cities on the Eastern Seaboard – including those that are not sinking — are at higher risk of coastal flooding in part because of their lack of physical protection, the researchers reported.
Much of the Gulf Coast is sinking rapidly, the study shows, though the number of people exposed to the flooding risk is not as high as the more populous East Coast. As much as a third of sea level rise in this region over the next three decades could come from the sinking effect, the report found.
On the Gulf, southern Louisiana is a hot spot for sinking land, as is southeast Texas, including the areas around Galveston, Freeport and Corpus Christi.
Why are coastal cities sinking?
Groundwater extraction is one of the primary drivers of coastal subsidence. Cities and industries are pumping water from underground aquifers faster than it can be replenished, a situation exacerbated by climate change-fueled drought. Excessive pumping lowers the water table and causes the overlying land to sink.
The same thing happens when oil and gas are extracted from underground. On and offshore, the Gulf Coast is dotted with oil and gas facilities, which not only contribute to the climate crisis that is exacerbating sea level rise but are also one of the leading causes of land subsidence in the region.
Other causes include seismic activity and soil compaction, either naturally from the weight of accumulating sediments over time or from heavy buildings pressing down on the ground, causing land to steadily sink. This is a particular problem in areas where new coastal land has been created over the years by backfilling with sediment.
A study last year found New York City is sinking under the weight of its own buildings.
“What’s interesting to me is that now, flooding is a game of inches,” said Kristina Hill, associate professor of environmental planning and urban design at the University of California at Berkeley, who is not involved with the study. “Our actions are catching up to us,” she said, noting that cities need to be wary of land subsidence when planning protective structures like levees and sea walls.
Researchers also looked at which communities are most vulnerable to sinking land and rising seas and found people of color and low-income populations on the Gulf Coast are disproportionately affected by the risk.
Here, people identifying as Black or African American account for more than half of those who will be exposed by 2050, despite only representing about 29% of the region’s total population, according to the report.
“For communities like New Orleans and Port Arthur, you’ll also see that the median value of property value is generally lower,” Ohenhen said. “And what that speaks to is that you generally have more presence of people with lower income in these areas exposed by 2050.”
Cities need to account for land subsidence as they adapt to the climate crisis and protect their communities from the growing threat of sea level rise, according to researchers. Otherwise, not accounting for land subsidence could lead to “inaccurate projections” of potential exposure.
Additionally, researchers say most sea level rise studies make projections for the end of the century, which “is viewed as too far (away) to begin planning,” Shirzaei said.
It’s a matter of knowing the risk and being proactive, he said, rather than waiting for an extreme event to happen to make changes.
