NASA: Moon ‘wobble’ will cause surge in coastal flooding in the 2030s

In the 2030s, flooding will increase on U.S. coasts, including along the California coastline, because of high tides triggered by a shift in the moon’s orbit and rising sea levels, NASA warns in a new study.

The study, published in the journal Nature Climate Change, is the first to consider how all known oceanic and astronomical factors will affect floods in the future, according to NASA. It predicts that U.S. mainland coastlines, Hawaii and Guam will see a surge in the number of floods in the mid-2030s.

The majority of the California coastline will experience three to four times more minor high-tide flooding throughout the decade, according to the study.

Based on models that take into account sea levels, tides and several other factors, the study forecasts when regions will begin to see a shift in flood frequency from one decade to another.

Based on intermediate sea level projections from the National Oceanic and Atmospheric Association, San Francisco and Humboldt counties will begin seeing increased flooding by 2037, according to study co-author Ben Hamlington of NASA’s Jet Propulsion Laboratory in Pasadena.

But nearby in Alameda, that transition won’t take place until 2051 because of a difference in factors such as sea level rise and flooding thresholds, he said.

The cause of increased high-tide flooding is that rising sea levels will coincide with something called a “wobble” in the moon’s orbit. The lunar cycle, which takes 18.6 years to complete, affects the strength of Earth’s daily tides.

For half of the cycle, low tides are higher than they typically are, and high tides are lower than usual. But during the other half of the cycle, low tides will decrease as high tides increase.

“Global sea level rise pushes high tides in only one direction – higher,” NASA explained in a statement. “So half of the 18.6-year lunar cycle counteracts the effect of sea level rise on high tides, and the other half increases the effect.”

In the 2030s, the lunar cycle will be in the phase that increases high tides. The study predicts that will cause more frequent flooding on the East and West Coasts, sometimes in clusters that could last more than a month.

“When the Moon and Earth line up in specific ways with each other and the Sun, the resulting gravitational pull and the ocean’s corresponding response may leave city dwellers coping with floods every day or two,” NASA added.

Regions of the East Coast that already are experiencing high-tide flooding will see the problem worsen, Hamlington said. Although flooding on the Pacific coastline currently is rare, the study predicts a dramatic increase in high-tide flooding.

“It’s almost going to be different perception of problem, but you’re going to see a pretty dramatic shift (on the West Coast), whereas on the East Coast people are dealing with this problem already,” he said.

The amount of flooding on the coasts won’t be as severe as during a hurricane, but it will have an effect on public health and the economy, Phil Thompson, an assistant professor at the University of Hawaii and the lead author of the study, told NASA.

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

The authors of the study hope that the information can be used to mitigate environmental and economic damage caused by increased flooding.

“When you start to get the pieces together, the impacts we’ll see is much more near term than in the distant future,” Hamlington said.