Almost all U.S. mainland coastlines in addition to Hawaii and Guam could see record high-tide flooding in the 2030s thanks to what is known as moon wobble.
Moon wobbles aren’t new, according to NASA. They are a cyclical shift in the moon’s orbit every 18.6 years and they’ve been recorded since 1728.
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The wobble affects the Moon’s gravitational pull and can either suppress or amplify ocean tides on Earth.
“In half of the Moon’s 18.6-year cycle, Earth’s regular daily tides are suppressed: High tides are lower than normal, and low tides are higher than normal,” according to NASA.
We are currently in the tide amplifying phase of the moon, but it’s the combination of the moon’s cycle paired with rising sea levels that is expected to increase the frequency of high-tide flooding, also known as sunny day flooding, during the moon’s next tide-amplifying cycle.
The NASA Sea Level Change Science Team from the University of Hawaii published a study in the Nature Climate Change journal that explains in greater detail why they expect to see a rapid increase in high-tide flooding in the coming years.
“Around the mid-2030s, locations along the Pacific and Gulf of Mexico coastlines will experience rapid increases in high-tide flooding frequency,” the study says.
The Gulf of Mexico coastlines were specifically mentioned as an area of concern because they are “more vulnerable to sea-level rise due to relatively narrow sea-level distributions.”
National Oceanic and Atmospheric Administration data was used to calculate the sea-level rise scenario.
“The mid-2030s marks the onset of an expected transition in high-tide flooding from a regional issue to a national issue with a majority of US coastlines being affected,” according to the study.
An article posted July 7 from the NASA Jet Propulsion Laboratory (JPL) states that “every U.S. coast will experience rapidly increasing high-tide floods when a lunar cycle will amplify rising sea levels caused by climate change.”
“The floods will sometimes occur in clusters lasting a month or longer, depending on the positions of the Moon, Earth, and the Sun,” according to the JPL article.
“Low-lying areas near sea level are increasingly at risk and suffering due to the increased flooding, and it will only get worse,” said NASA Administrator Bill Nelson.
Compared to hurricane storm surges, high-tide floods only involve a small amount of water.
“But if it floods 10 or 15 times a month, a business can’t keep operating with its parking lot underwater. People lose their jobs because they can’t get to work. Seeping cesspools become a public health issue,” said Assistant Professor at the University of Hawaii Phil Thompson. He is the lead author of the study.
Flood numbers from 89 tide gauge locations in every coastal U.S. state and territory but Alaska were studied by researchers who discovered the mid-2030s flooding projection.