A new study on high tide flooding predicts that the mid-2030s could be catastrophically wet in U.S. coastal regions — and it could stay that way for an entire decade.
Led by members of the NASA Sea Level Change Team from the University of Hawaii, the study says that high tide flooding could happen more frequently on several U.S. coasts. Flooding at high tide, often called nuisance flooding, already occurs with regularity in many coastal communities as water routinely sloshes into streets, yards and businesses.
Two factors could converge to worsen flooding at high tide, the study says: rising sea levels fueled by climate change — and the moon.
The moon is about to "wobble"
The moon's orbit is due for its regular "wobble." That is entirely natural, NASA says, and it has been recorded as far back as 1728. Half of the moon's 18.6-year cycle creates lower high tides and higher low tides; the other creates higher high tides and even lower low tides.
But NASA says global sea level rise will likely push those high tides higher, and one of the study's co-authors, NASA Sea Level Change Team leader Ben Hamlington, said that because waters will be higher, this moon cycle could have a much more dramatic effect.
"We're getting closer and closer to the flooding thresholds or tipping point in these coastal locations," he said. "The same variability in the past that didn't cause flooding is now going to cause flooding."
High tides already exceed known flooding thresholds around the United States. The National Oceanic and Atmospheric Administration reported continued record-setting high tide, or sunny day, flooding in 2019. But the study shows that high tides will exceed flooding thresholds more often. Floods, the study predicts, could also start occurring in "clusters" that last a month or longer, depending on how the sun, moon and Earth are positioned, according to NASA.
"Low-lying areas near sea level are increasingly at risk and suffering due to the increased flooding, and it will only get worse," NASA Administrator Bill Nelson said. "The combination of the moon's gravitational pull, rising sea levels and climate change will continue to exacerbate coastal flooding on our coastlines and across the world."
Coastal cities have already started to act, but dramatic flooding is coming faster than many once thought
Hamlington said cities and urban planners along the coasts that are already familiar with high tide flooding have been acting to prevent future damage, but the study's assessment means higher hides and longer floods are coming faster than anticipated.
"A lot of the projections that we as scientists give to coastal planners are up to 2100, but the impacts that we're going to see because of how these different factors and processes are combining are much nearer term," he said. "We're going to see these big dramatic shifts in the next decade or two."
Josie Fischels is an intern on NPR's News Desk.
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