Rising sea levels will cause surge of flooding under moon’s ‘wobble’

15 Jul 2021

Image: © Patricia/Stock.adobe.com

A leap in flood numbers predicted to begin in the mid-2030s could affect most US coastal cities almost daily and last over a month at a time.

A new NASA study has found that rising sea levels caused by the climate crisis will increase the incidence of high-tide floods on US coasts in the mid-2030s.

The study, led by a team of NASA researchers from the University of Hawaii, assessed all known causes for floods and found that the lunar cycle will be a factor in causing the predicted record-level floods.

This is because the increasing rate of global sea level rise will meet with a routine ‘wobble’ in the moon’s orbit. The change in gravitational pull from the moon in this phase will exacerbate the issue already caused by the climate crisis.

The moon’s orbital wobble was first detected in 1728 and is a regular occurrence in the moon’s 18.6 year cycle. We are about to enter into the second half of this cycle, where the moon’s gravitational pull will cause tides to be amplified. High tides will be higher and low tides will be lower.

NASA’s researchers predict that by the time the amplifying stage of the moon’s cycle rolls around again in the mid-2030s, global sea level rise will have continued for another decade. With higher seas under its influence, a surge in flooding is predicted.

The coast is not clear for US cities

While flooding during high tide is not uncommon on the US Atlantic coast, the study found that continuous rise in sea levels means that many more locations will now experience recurrent floods.

The higher sea levels in tandem with the lunar cycle will cause a leap in flood numbers on almost all US mainland coastlines, Hawaii and Guam.

Only far-northern coastlines, such as those in Alaska, will be spared for another decade or longer because this region’s land areas are rising as a result of long-term geological processes.

The study found that the floods may occur in clusters lasting a month or longer, depending on the positions of the moon, Earth and sun. Sometimes, coastal cities may even experience flooding almost daily.

NASA administrator Bill Nelson said that low-lying areas near sea level are increasingly at risk and suffering due to the increased flooding, and that it will only get worse.

“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,” he said.

NASA’s sea level change team, the group of researchers behind the study, is providing crucial information to help plan, protect and prevent damage to the environment and people’s livelihoods from flooding.

“It’s the accumulated effect over time that will have an impact,” said Phil Thompson, assistant professor at the University of Hawaii and lead author of the study.

He said that because high-tide floods involve a small amount of water compared to hurricane storm surges, there’s a tendency to view them as a less significant problem overall.

“But if it floods 10 or 15 times a month, a business can’t keep operating with its parking lot under water. People lose their jobs because they can’t get to work. Seeping cesspools become a public health issue,” Thompson added.

The researchers studied 89 locations across US coastal states and created a new statistical framework that mapped data taken from the National Oceanic and Atmospheric Administration (NOAA).

“From a planning perspective, it’s important to know when we’ll see an increase,” said Ben Hamlington, leader of NASA’s sea level change team and co-author of the study.

“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,” he said.

NOAA reported a total of more than 600 high-tide floods in the US in 2019.

The study was published in Nature Climate Change, a London-based monthly journal that publishes research on the nature, causes and impacts of climate change and its implications for the economy.

Vish Gain is a journalist with Silicon Republic