During summer of 2017, the tide reached historic highs again and again in Honolulu, higher than at any time during the 112-year record retention period. Philip Thompson, director of the Sea Level Center at the University of Hawaii, wanted to know why. “Where did it come from?” He asked. “How often is this going to happen? Is this our window to the future? “
What Thompson and a group of researchers discovered that the future has arrived. The summer of 17 was a glimpse of the aquatic reality to come in Honolulu and other coastal communities. The study, published in June in Natural climate change, found that higher and more frequent tides will reach an inflection point in the 2030s, especially along the west coast and on islands like Hawaii’s, which has been called “untimely flooding” common.
“Many areas along the East Coast are already experiencing recurring impacts,” says Thompson. “In the mid-2030s, these other areas will catch up quickly. So it’s a transition from a regional problem on the east coast to a national problem, where the majority of the country’s coasts are regularly affected by flooding at high tide. “
What regularity? The study, which included researchers from NASA and the National Oceanic and Atmospheric Administration, shows that flooding from sunny days will cluster in the fall, creating a nightmare for cities and businesses. Streets will be impassable, cars will be damaged in parking lots and storm water systems will be strained. Additionally, tidal flooding also taints local waterways with pollutants including petroleum, gasoline, trace metals and nitrogen, causing algae blooms that create oxygen-depleted dead zones.
Thompson notes that high tide flooding is subtle, damaging a community with a thousand blackouts or, in this case, dozens of days a year where getting to work or shopping for groceries becomes a problem, if not impossible. “If it happens 10 or 15 times a month, it becomes a problem,” he adds. “A business can’t keep operating with its parking lot underwater. People lose their jobs because they can’t get to work. These impacts can really add up quickly.”
The study adds to growing research into the variables that lead to increasingly high tides. Like sea level rise, flooding at high tide varies from place to place. Some of the factors that increase flooding caused by sunny days include local land subsidence, the effects of El Niño, the slowing of the Gulf Stream along the Atlantic coast, water temperature and ocean eddies.
While the role of the so-called “wobble” of the moon in harmful flooding has grabbed the headlines, this is nothing new and the label is misleading. The moon is don’t waver; its angle to the earth’s equator changes very slightly as it orbit, which was first reported in 1728. The cycle lasts 18.6 years. Half of this time it suppresses the tides, and during the other half it amplifies them. The effect is especially strong in places that have a single high tide or a dominant high tide for a single day, such as much of the west coast.
While the angle of the moon is now amplifying the tides, sea level rise has not been large enough in some places to exceed flood thresholds. That will change over the next cycle in the 2030s, the study concludes. These higher sea levels coupled with another lunar cycle will lead to a nationwide surge in high tide flooding, starting with what Thompson and the researchers call “a year of inflection.”
These years will differ from place to place due to local variables. This means that La Jolla will probably have 15 flood days at high tide in 2023, 16 days in 2033 and 65 days in 2043. In Honolulu, they predict two flood days in 2033 and 65 days in 2043. In St. Petersburg , in Florida, the jump goes from seven days in 2023 to 13 days in 2033 and then to 80 days in 2043.