Abstract—earth and the moon to scale.(Credit: Bluedharma/Flickr Commons)

Recent floods around the world in Germany, China, India, Afghanistan and the US are causing scientists to debate the use of “once in a century” or “once in a millennium” terminology when referring to extreme flooding events.

In the coming decade, sea-level rise from climate change, combined with a lunar cycle that takes place every 18.6 years, could exacerbate coastal flooding. A report led by NASA’s Sea-level Change Science Team from the University of Hawai’i describes how the natural “wobble” in the moon’s orbit could worsen coastal flooding events, affecting business and urban development.

The report, entitled “Rapid increases and extreme months in projections of United States high-tide flooding,” describes how in the mid-2030s, US coastal regions could see an increase in high tide flooding. While the report focuses on how the US will be affected by the flooding, the lunar nodal cycle that causes the moon’s orbital “wobble” could exacerbate flooding incidences in coastal regions worldwide.

The moon’s “wobble” was first recorded in the 1700s and has been compared to the way a spinning coin undulates just before falling flat. Though the term “wobble” implies an irregular occurrence, the phenomenon takes place cyclically every 18.6 years.

During half of the cycle, Earth’s regular tides are reduced, with high tides lower than normal and low tides higher than normal. Despite flooding in many regions, the world is currently in a cycle of reduced tides.

The next lunar nodal cycle is expected to increase tides, though the extent will vary by region. Tides may increase by only a few inches, but those few inches could burden businesses and homeowners alike by flooding parking lots and backing up sewer systems.

According to Brian McNoldy, Senior Research Associate at the University of Miami, “During the most rapid downward phase of the lunar nodal cycle—like we’re in right now—we have a bit of a reprieve in the observed rate of sea-level rise, all other things being equal…

Once we reach the bottom of the cycle around 2025 and start the upward phase, the lunar nodal cycle contributes more and more to the perceived rate of sea-level rise. During those years, the rate of sea-level rise is effectively doubled in places like Miami.”

Incremental damage often causes governments to be complacent in their mitigation efforts. Even though the sea-level rise is imminent, more people are still moving to coastal cities instead of inland areas.

The University of Hawai’i, which collaborated on the project with NASA, published an article discussing the importance of making coastal communities more resilient to flooding while there is time. Instead of waiting to repair damage after it happens, experts implore lawmakers and city planners to act now when the moon’s cycle offers more favourable conditions.

Economic factors stand in the way of many coastal cities doing what needs to be done to prepare for sea-level rise.

Miami has seen regular flooding over the years and has released plans to elevate homes and roads, but economic factors make officials reluctant to dissuade businesses and residents from moving to the area. Poorer and less densely populated areas rarely generate enough tax revenue to fund flood mitigation projects, meaning that such projects may only happen in wealthier areas.

Climate change does not occur in a vacuum, but along with the earth’s natural cycles. Many of the major flood events of the past year—Henan Province, China; Utah, US; Rajasthan, India; Nuristan Province, Afghanistan—did not occur in coastal areas, lending proof to the fact that the current lunar nodal cycle is keeping tides lower. Coastal areas are still at the highest risk of damage due to climate change.

Sea-level rise combined with the lunar “wobble’s” tidal increases could make high tide flooding incidents 50 per cent more frequent in some regions. If governments overseeing coastal cities act decisively now, during the lull, and invest in mitigation projects, they may save lives.

Sarah Sakeena Marshall
Staff Writer, Grit Daily
Environmental Columnist, The Muslim News