Space – NOAA projections and a NASA study show Charleston is in for more tidal flooding | News
Charleston had a record-breaking amount of significant tidal flooding from May 2020 to April 2021, according to officials with the National Oceanic and Atmospheric Administration.
NOAA recorded 14 days of high-tide flooding at its Charleston Harbor gauge in that period. For the next year, it predicts less, between five and nine days of disruptive flooding.
NOAA’s flooding thresholds are higher than those used by the National Weather Service to warn about potential tidal flooding in Charleston, and are meant to capture more-disruptive events. But both measures have logged record-breaking high tides in recent years.
At the same time, a new study led by scientists at NOAA, the University of Hawaii and the National Aeronautics and Space Administration showed that Charleston will hit an inflection point in 2025, ushering in a decade of even more tidal events because of the compounding effects of sea-level rise on top of the quirks of the moon’s orbit around the Earth.
On a call with reporters on July 14, NOAA oceanographer William Sweet said that the Southeastern United States, in particular, has consistently outstripped tidal flooding projections of late. In 2019, for example, persistently swollen oceans swamped the coast from Florida through the mid-Atlantic. Charleston’s flooding tally from 2020 to 2021 was also double what federal scientists had forecast the year before.
It’s still unclear if these wetter-than-expected periods are an anomaly or if the trend of sea rise, driven by a warming planet, is simply faster than anticipated, Sweet said.
Climate change, or the rise of average temperatures over land and water, makes the ocean rise in two ways. Melting ice adds more water to oceans, and hotter water expands, taking up more space. It’s that second factor that seems to be contributing in part to the anomalous flooding in the Southeast, Sweet said, as coastal waters from the surface to their depths consistently warm up in the region.
Scientists may have to push their predictions even higher in the future if the trend holds. But a reduction in the causes of heating — planet-insulating gases that come mostly from burning fossil fuels — could turn the tide.
The trend is “conditional upon human responses, largely, and that we can’t predict,” Sweet said.
At the same time, this trend is on a collision course with long-documented nuances in the lunar orbit, according to a study published in the journal Nature Climate Change last month.
A slow-motion “wobble” in the moon’s orientation toward Earth has long been known to affect tidal cycles, said Ben Hamlington, an author of the paper and leader of NASA’s sea-level change team. In one part of this 18.6-year cycle, high tides push higher and low tides drop further; in the other phase, the differences between the two extremes flatten out.
Analysis of that well-known pattern and the general rate of sea-level rise showed that most coastal communities around the United States will start seeing an even more active phase of flooding in the mid-2030s, according to the paper. Sweet was also a collaborator on the research.
But in Charleston, that point actually comes earlier, in 2025. After that year, the Holy City will see 36 more days of significant tidal flooding in a year, on average, than the decade before — an almost threefold increase.
Hamlington cautioned that the inflection point is a gradual one, and that the increased flooding will ramp up over the next 10 years. But it’s one of many indicators that tidal flooding is bound to become more severe.
“We’ve had nodal (lunar) cycle shifts in the past that didn’t cause a huge amount of flooding,” he said. “It’s how these things stack up and combine.”
Reach Chloe Johnson at 843-735-9985. Follow her on Twitter @_ChloeAJ.