As sea levels rise, B.C. coastal cities could face flooding from moon's 'wobble'

A lunar cycle that repeats only once every 18.6 years could combine with rising seas from climate change, and create further problems here on Earth.

What some are calling a"moon wobble" means B.C.'s coastal communities that arealready bracing for floodingfrom rising sea levelsmay also have to contend with an added phenomenon.

"Nothing about the moon is changing, this is a totally predictable effect," explainedJess McIver, an assistant professor of astronomy at UBC. "It's been wobbling in this way for millions and millions of years.

"Very, veryslowly the axis the moon is orbiting the Earth around is kind of shifting ... and the tides are going to respond."

The issue came to the fore after the release of a new NASA study, publishedin Nature Climate Changejournal earlier this month, called "Rapid increases and extreme months in projections of United States high-tide flooding."

Although the study only examines impacts on U.S. coastal communities, the same effects would apply to cities in B.C. as well as other coastal areas in Canada, explained McIver.She added that the effects of moon wobble would vary by location.

She said she hopes further studies can specifically examine how the phenomenon, known formally as a "precession effect" of the lunar cycle,could impact Canadian tides.

The effect will not become significant until the 2030s, according to NASA, butthat's exactly when rising sea levels are forecastto worsen.

Cities on B.C.'s coasthave already begun preparingfor rising sea levels, flooding and extreme tides, in addition to the other climate and weather extremes predicted by climate scientists.

And although they have long known oceans will likely encroach on some urban areas, the addition of the lunar "wobble" at almost exactly the same time could amplify the impact.

King tides flood West Van seawall

10 years ago

Duration 0:57

King tides are unusually strong and occur around the solstice

"We're going to have this overlap between this very predicted steady creep up in sea level," McIver said. "And when you combine that with this normal 19-year cadence, all of a sudden we're going to reach a point where we start seeing this flooding a lot more often."

The new study is yet another warning to low-lying cities such as Richmond, Delta, Victoria and many First Nations along the coast, saidKees Lokman, chair of landscape architecture at UBC.

Lokman is also principal investigator on a four-year research project, Living With Water, which is examining how cities and First Nations can adapt to climate change and flooding. The project is based out ofthe University of Victoria'sPacific Institute for Climate Solutions.

"If we don't really plan ahead, it will impact us pretty drastically, especially with these new findings," Lokman said. "Some of these rises to sea level might happen faster than we originally predicted or anticipated."

The City of Richmond is one municipality that has heavily invested in dikes and flood protections in its climate plan.

The city is built just one metre above sea level, and in 2019 was one of several B.C. municipalities to officially declare a climate emergency.

"A considerable amount of upgrades and improvements to the city's flood protection infrastructure have been completed and are planned for the short-, medium-, and long-term to address infrastructure age, growth and climate change," Richmond said on its website.

Theprovince's environment minister, in his most recent mandate letter, wastasked with creating "acoastal strategy to better protect coastal habitat" and protecting the coast's economy.

Lokman says mitigation of B.C.'s contributions to greenhouse gases should be a priority, but also how communities can adapt torising sea levels from climate change.

He sayseffects from the moon wobble could also help communities and policy makers address climate change.

"These events kind of give us a peek into the future of what normal sea level rise might look like," he said.

• Report:NASA study on extreme months and high-tide flooding (Nature Journal)