A moon “wobble” is expected to bring a surge in extreme flooding in the 2030s, NASA scientists have warned.
Rising sea levels, caused by climate change, will be amplified by the moon’s orbit which has a natural “wobble” every 18.6 years and affects the Earth’s tides.
Such weather — also known as nuisance floods or sunny day floods — can also overwhelm drains, close roads and affect infrastructure.
Hawaii and Guam are also likely to suffer a leap in high-tide floods due to pressure from higher sea levels in 2023.
However, northern coastlines such Alaska’s will be spared for at least another decade thanks to rising land areas due to long-term geological processes.
“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.
“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.”
Phil Thompson, an assistant professor at the University of Hawaii and lead author of the study, said it’s “the accumulated effect over time that will have an impact”.
He explained how there is a tendency to view high-tide floods as a smaller problem overall because they involve less water compared to hurricane storm surges.
“But if it floods 10 or 15 times a month, a business can’t keep operating with its parking lot under water,” he added.
“People lose their jobs because they can’t get to work. Seeping cesspools become a public health issue.”
High-tide floods are already a familiar problem in many cities on the US Atlantic and Gulf coasts.
More than 600 such floods were reported in 2019 by the National Oceanic and Atmospheric Administration (NOAA).
Starting in the mid-2030s, however, the combination of rising sea levels and the lunar cycle will cause a dramatic increase in flood numbers across US coastal cities, the new study found.
Published by Nature Climate Change, NASA’s sea level change science team, it is the first to consider all known oceanic and astronomical causes for floods.
High tides will exceed known flooding thresholds around the country more often, researchers found.
The 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.
Ben Hamlington of NASA’s Jet Propulsion Laboratory in Southern California, a co-author of the paper, noted that the findings are a vital resource for coastal urban planners who may be focused on preparing for extreme events rather than more high-tide floods.
“From a planning perspective, it’s important to know when we’ll see an increase,” he said.
“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.”
A high-tide flood tool already exists on the NASA team’s sea level portal, a resource for decision-makers and the general public and it due to be updated following the findings.