A study, led by the members of NASA Sea Level Change Science Team from the University of Hawaii, has predicted a decade of “dramatic increases” in flood numbers around the world, especially in the US, starting mid-2030s. The study, touted to be the first such, takes into account all known oceanic and astronomical causes for floods.

According to the study, every U.S. coast will experience rapidly increasing high-tide floods, when a lunar cycle will amplify rising sea levels caused by climate change. It showed that high tides will exceed known flooding thresholds around the country more often. Further, it claimed that floods will sometimes occur in clusters lasting a month or longer, depending on the positions of the Moon, Earth and the Sun.

“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,” the study noted.

According to NASA administrator Bill Nelson, 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. NASA’s Sea Level Change Team is providing crucial information so that we can plan, protect, and prevent damage to the environment and people’s livelihoods affected by flooding,” he said.

If one goes by the words of Phil Thompson, who is an assistant professor at the University of Hawaii and the lead author of the new study, it’s the accumulated effect over time that will have an impact. Thompson pointed out 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.”

MOON – WOBBLE EFFECT
Now, the question is: Why will cities on such widely separated coastlines begin to experience these higher rates of flooding at almost the same time?

According to the study, the main reason is a regular wobble in the Moon’s orbit that takes 18.6 years to complete. The study clarified that there was “nothing new or dangerous” about the wobble. It was first reported in 1728. What’s new is how one of the wobble’s effects on the Moon’s gravitational pull – the main cause of Earth’s tides – will combine with rising sea levels resulting from the planet’s warming.

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. In the other half of the cycle, tides are amplified: High tides get higher, and low tides get lower. Global sea level rise pushes high tides in only one direction – higher. 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, the study explained.

As per the study, the higher seas, amplified by the lunar cycle, will cause a leap in flood numbers on almost all U.S. mainland coastlines, Hawaii, and Guam. Only far northern coastlines, including Alaska’s, will be spared for another decade or longer because these land areas are rising due to long-term geological processes, it said.

The researchers uncovered these tipping points in flood numbers by studying 89 tide gauge locations in every coastal U.S. state and territory but Alaska. They created a new statistical framework that mapped NOAA’s widely used sea level rise scenarios and flooding thresholds, the number of times those thresholds have been exceeded annually, astronomical cycles, and statistical representations of other processes, such as El Niño events, that are known to affect tides. They projected results to 2080.