Where sinking US cities are pushing sea level rise into overdrive

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.

https://www.ocregister.com/2024/03/07/where-sinking-us-cities-are-pushing-
sea-level-rise-into-overdrive/