Charleston SC One Of US' Fastest-Sinking & Most Flood-Prone Cities; New Developments Continue Apace

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The increasing floods are prompting insurance companies to raise premiums and decline policy renewals, creating incentives for residents to leave their homes. In fact, zip codes in coastal South Carolina are among those with the highest insurance non-renewal rates, according to a Brookings Institution analysis. Charleston was built along the confluence of three rivers and the Atlantic Ocean, on marshland and mud flats. Flooding there was once far less frequent. But now, even an afternoon thunderstorm or an unusually high tide can overwhelm drainage systems and submerge streets. The sea level in Charleston rose about 13in over the past century, according to the National Oceanic and Atmospheric Administration, and by 2100 it’s expected to rise about 4ft more.

Charleston is also one of the most rapidly sinking cities in the United States, mainly because of groundwater pumping and the settling of natural sediments and filled marsh areas. That double threat – rising seas and sinking land – leaves the city increasingly exposed to flooding. According to Climate Central’s Coastal Risk Finder, more than 8,000 people and 4,700 homes in Charleston county will be at risk of annual flooding by 2050, even under moderate climate action scenarios. By 2100, more than 60,000 people could be affected. Rapid development, meanwhile, is paving over forests and wetlands that once soaked up stormwater. Every new subdivision and strip mall replaces absorbent ground with impervious surfaces – asphalt, rooftops, parking lots – that send rainwater rushing into neighborhoods such as Rosemont.

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Long Savannah is expected to bring up to 4,500 homes. It’s one of several massive projects rising across Charleston county, including Magnolia Landing and Cainhoy, 4,000- and 9,000-home developments. The developers of Long Savannah have received approval to fill and excavate wetlands, which environmentalists say are crucial to soaking up rain and keeping flooding in check. The developers of Long Savannah and Magnolia Landing did not respond to requests for comment. A spokesperson for Cainhoy noted that the project was on higher ground than other flood-prone areas, and that 3,500 acres of wetlands will be preserved.

In the Cainhoy case, a federal judge in 2022 dismissed flooding concerns, citing a US army corps of engineers report, which concluded the development has a “high percentage of wetlands and … numerous direct outfalls to tidal waters that will minimize the potential for heavy rains to overwhelm its infrastructure.” “Charleston has a history of building in repetitively flooded areas,” said Robby Maynor, a climate campaign associate with the Southern Environmental Law Center, which, along with other environmental groups, contested a decision by state environmental officials to allow new development on wetlands in the Long Savannah project. “We absolutely must stop building in low-lying and flood-prone areas to avoid making an already difficult situation even worse.”

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https://www.theguardian.com/environment/2025/sep/09/charleston-rising-seas