Flooding along U.S. coasts is expected to be a worse problem starting in the 2030s due to the combination of a “wobble” in the moon’s orbit and rising sea levels resulting from climate change, according to a new NASA study.


What You Need To Know

    • Flooding along U.S. coasts is expected to be a worse problem starting in the 2030s due to a “wobble” in the moon’s orbit and rising sea levels resulting from climate change, according to a new NASA study
    • The researchers have projected that there will be a decade in which the number of floods will dramatically increase, impacting almost all U.S. mainland coastlines, Hawaii and Guam
    • High-tide floods will occur more often and could sometimes happen in clusters lasting a month or longer, depending on the positions of the moon, Earth and sun, according to the study
  • High-tide floods involve less water than hurricane storm surges, but their accumulated effect over time could be a significant problem, said Phil Thompson, the study’s lead author

Researchers from NASA’s Sea Level Change Science Team at the University of Hawaii have projected that there will be a decade in which the number of floods will dramatically increase, impacting almost all U.S. mainland coastlines, Hawaii and Guam.

High-tide floods — already a headache for many low-lying communities along the East and Gulf coasts — will occur more often and could sometimes happen in clusters lasting a month or longer, depending on the positions of the moon, Earth and sun, according to the study, which NASA says is the first to take into account all known oceanic and astronomical causes for floods. According to the the National Oceanic and Atmospheric Administration, there were 600 high-tide floods in 2019.

“Low-lying areas near sea level are increasingly at risk and suffering due to the increased flooding, and it will only get worse,” NASA Administrator Bill Nelson said in a news release. “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.”

Nelson said NASA hopes the information will be used to “plan, protect, and prevent damage to the environment and people’s livelihoods.”

The moon’s wobble affects its gravitation pull, the main cause of the rise and fall of ocean tides on Earth. The wobble is a regular part of the moon’s 18.6-year orbit and is not dangerous on its own. But it is expected to worsen the challenges created by rising sea levels, according to the study, which was published in the journal Nature Climate Change.

During half of the moon’s orbit, tides are amplified — high tides are higher, low tides are lower — and for the other half, they are suppressed — high tides are lower than normal, but low tides are higher. The moon is currently in the tide-amplifying stage of its cycle, but sea levels are not yet high enough to regularly top flooding thresholds. That won’t be the case in the mid-2030s, the next time the tides are amplified, the scientists said.

High-tide floods involve less water than hurricane storm surges, but their accumulated effect over time could be a significant problem, said Phil Thompson, an assistant professor at the University of Hawaii and the study’s lead author.

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

Amsterdam, the Netherlands

1. Amsterdam, the Netherlands

There’s a reason they’re called the Low Countries. Amsterdam and the cities of Rotterdam and the Hague sit low, flat and close to the North Sea. The Dutch are famed for their flood defences, and looking at these sea-level projections, it seems the country’s system of dikes, dams, barriers, levees and floodgates will become even more essential in the years to come.

Basra, Iraq

Image: Climate Central

2. Basra, Iraq

Iraq’s main port city of Basra lies on the Shatt al-Arab, an enormous and wide river that feeds into the Persian Gulf. Due to its intricate network of canals and streams, as well as neighbouring marshland, Basra and its surrounding areas are especially vulnerable to a rise in sea levels. And as if that wasn’t worrying enough, Basra already suffers significantly from waterborne diseases – so increased flooding carries even more significant threats.

New Orleans, USA

Image: Climate Central

3. New Orleans, USA

See those sharp, thick grey borders on the above map around the centre of New Orleans? That’s the city’s system of levees that protects it from the swarm of red building up from Lake Maurepas in the north and from Lake Salvador and Little Lake in the south. Without those defences, New Orleans would be severely threatened by rising sea levels, but even with them, the damage looks catastrophic. The Biloxi and Jean Lafitte wildlife preserves look particularly vulnerable – on the map both appear almost totally submerged.

Venice, Italy

Image: Climate Central

4. Venice, Italy

In the very near future, Venice faces a twin threat: sea levels are rising and the city itself is sinking – by two millimetres every year. The Venetian capital has already been hit by servere flooding, and climate change is likely to increase the frequency of high tides that submerge it. Like New Orleans, Venice has a system of flood-defence systems in place, but as the crisis worsens, these will be more difficult (and expensive) to maintain.

Ho Chi Minh City, Vietnam

Image: Climate Central

5. Ho Chi Minh City, Vietnam

Climate Central’s map shows that the areas most at risk in Ho Chi Minh City are its eastern districts – particularly the flat, heavily built-up marshland of Thủ Thiêm. But it also looks like the city will be increasingly threatened along the Mekong Delta. While the centre of Ho Chi Minh City itself is unlikely to find itself underwater by 2030, it will almost certainly be more vulnerable to flooding and tropical storms.

Kolkata, India

Image: Climate Central

6. Kolkata, India

Much of west Bengal has thrived for centuries because of its fertile landscape, but as the map above shows, that has become great cause for concern in Kolkata and its surroundings. Like Ho Chi Minh City, the city could struggle during monsoon season as rainwater has less land to run off into. This map of the potential situation in 2100 is even more concerning.

Bangkok, Thailand

Image: Climate Central

7. Bangkok, Thailand

2020 study found that Bangkok could be the city that’s worst hit by global warming in the short term. The Thai capital sits just 1.5 metres above sea level and, like Venice, it’s sinking (only much, much faster – by about two to three centimetres a year). But Bangkok is also built on very dense clay soil, which makes it even more prone to flooding. By 2030, most of the coastal Tha Kham and Samut Prakan areas could be underwater, as could its main airport, Suvarnabhumi International.

Georgetown, Guyana

Image: Climate Central

8. Georgetown, Guyana

For centuries, Guyana’s capital Georgetown has relied on sea walls – or, more accurately, one gigantic, 280-mile long sea wall – for protection from storms. That’s because most of the coastline is between 0.5 and one metre below high tide. Some 90 percent of Guyana’s population lives on the coast, and as you can see, the country will need to substantially bolster its sea wall if Georgetown’s central areas are to avoid massive damage.

Savannah, USA

Image: Climate Central

9. Savannah, USA

The city of Savannah, Georgia sits in a hurricane hotspot, but even without extreme weather events, the historic city could see land swallowed up by the sea on all sides. The Savannah River in the north and Ogeechee River in the south could both spill out into the nearby marshland, meaning that when hurricanes and flash floods do hit the city (and by 2050 the city is predicted to experience once-per-century historical flood levels every year), the effects may be even more severe.

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