- In Charleston, high tide flood days are expected to increase.
- Scientists are trying to find out what causes the land sinking in the region.
- But they say rising sea levels remain a major concern.
Images of water flowing through the streets and up the sidewalks in Charleston, South Carolina, are becoming more and more common.
The city is no stranger to what is known as a flood of sunny days, which happens during high tides, even in the best weather, and is aggravated by rising sea levels.
But scientists are also looking to understand the role that subsidence, or sinking, can play.
Data from a NOAA meter in Charleston show that about 5 of the 30 centimeters of sea level rise there over the past 100 years can be attributed to subsidence. It is not clear why the earth is sinking.
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One theory: it has to do with soil compression caused by large buildings, highways and other growing developments.
“We had buildings on the peninsula. Now we are getting much larger buildings on the peninsula,” Norm Levine, director of the Lowcountry Hazards Center at the College of Charleston, told the Post and Courier. “If we get there now and measure things, we can start to understand susceptibility.”
The streets in some parts of Charleston are covered in water several times a year. This week, a combination of seasonal tidal kings, winds behind a cold front and Hurricane Teddy in the Atlantic led to major coastal floods in the city. A wave of 2.5 meters or more was measured three days in a row – something that has never happened before in records dating from 1934.
Extreme tides were seen in satellite images.
Twenty years ago, Charleston experienced two days of flooding a year, according to the NOAA high tide bulletin. That number reached a record high of 13 last year. In 2050, the city may have up to 90 days of flooding a year.
Subsidence is exacerbating rising sea levels in areas such as the Louisiana coast, where lands essential for protecting inland areas are disappearing.
While scientists are looking to find out more about subsidence in and around Charleston, they say this is not the main cause of flooding on sunny days.
“The rate of sea level rise is faster,” said Levine.
The forecast is that it will continue like this, with the sea level rise accelerating even more. But understanding subsidence can help with future planning and mitigation measures.
“Vertical land movement is big business, and we really don’t have a lot of control over regional differences,” Doug Marcy, a Charleston-based NOAA coastal risk specialist, told the Post and Courier.
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