Moon’s ‘wobble’ could lead to higher flooding on coasts, NASA says

by Charles Hilu  | July 18, 2021 09:00 AM

People living in coastal areas may see record flooding caused by the moon in the next decade or so.

Astronomical cycles, coupled with rising sea levels from climate change, may cause a surge in coastal flooding beginning in the mid-2030s, according to a study from NASA released on July 7.

“Why will cities on such widely separated coastlines begin to experience these higher rates of flooding at almost the same time? The main reason is a regular wobble in the Moon’s orbit that takes 18.6 years to complete,” the agency said.


First recorded in 1728, the wobble has an impact on the severity of the ocean’s tides caused by the moon’s gravitational pull. The first portion of the cycle reverses the effects of tides, making high tides lower and low tides higher. The second portion amplifies the tidal effects, making high tides higher and low tides lower.

“The Moon is in the tide-amplifying part of its cycle now,” NASA said. “However, along most U.S. coastlines, sea levels have not risen so much that even with this lunar assist, high tides regularly top flooding thresholds. It will be a different story the next time the cycle comes around to amplify tides again, in the mid-2030s. Global sea level rise will have been at work for another decade.”

NASA scientists studied a total of 89 locations spread across every coastal state and territory, examining various flooding scenarios from NOAA’s sea-level database and correlating the data with lunar cycles. They can predict tide levels from states such as Virginia and California as far into the future as 2080.

The only coastlines that are not projected to see an increase in flooding are Alaska’s due to the rising of land areas in the state.

Coastal dwellers might see their cities flooded in monthlong clusters that yield a flood almost every day, the study found.

“From a planning perspective, it’s important to know when we’ll see an increase. Understanding that all your events are clustered in a particular month, or you might have more severe flooding in the second half of a year than the first — that’s useful information,” said Ben Hamlington, a co-author of the study who leads NASA’s Sea-Level Change Team.

The Gulf Coast coast and southern Atlantic coast saw serious increases in high tide flooding days in 2020. Most areas were hit with an increase of at least 300%, while others witnessed increases as high as 1,100%, according to data from NOAA.

Leave a Reply

Your email address will not be published.