So-called king tides — the highest of high tides — are especially high (and low) tides that occur at least twice a year, when the gravitational forces of the sun, the moon, and Earth’s rotation align perfectly to maximize the tidal “bulge” of Earth’s oceans. The most extreme king tides, like those expected this week, are viewed as a preview of what might become the “new normal” as sea levels continue to rise. As such, they offer an opportunity to describe and analyze the impacts and possible responses to the vulnerabilities that appear inevitable.
In Alexandria, Va., high tide will peak around 3.6 feet on Wednesday and Thursday, which is around the maximum high tide ever recorded at the location. This does not include effects from wind, which tend to increase or decrease tide levels, depending on direction.
As early as Sunday, the afternoon’s high tide along the Potomac had already washed over the road leading to Haines Point, putting a hard stop on my bike ride amongst many bewildered bikers, pedestrians, and drivers staring at the unexpected road block. I’ve also heard anecdotal reports from the Maine coast, where residents said they had never seen the tides rise so high.
While king tides are as natural and predictable as the moon rise, they enter murky water when they are superimposed on rising sea levels due to the warming of oceans and runoff from melting glaciers. As terrible as the devastation was during Superstorm Sandy, and significant losses to a lesser degree by Hurricane Irene as well as major winter coastal storms, it’s not hard to imagine how much worse it could be in a future where extreme high tides become the norm.
Sea levels are rising and will continue to rise with increasingly consequential impacts on societal norms and infrastructure along low-lying coastal regions, especially large cities. In the Miami region, for example, Capital Weather Gang tropical expert Brian McNoldy describes how sea level has risen 4.5 inches between 1996 and 2013. “The mean sea level has risen noticeably in the Miami and Miami Beach areas just in the past decade,” McNoldy writes. “Flooding events are getting more frequent, and some areas flood during particularly high tides now: no rain or storm surge necessary.”
More alarmingly, McNoldy finds in just the past five years, the average increase in the height of high tide has accelerated from 0.19 inches to 0.67 inches per year. This has resulted in an increased frequency of flooding not only along Florida’s southeastern coastal beach fronts, but has caused widespread flooding over areas further inland, especially during high tides. Importantly, the incidences of flooding mostly occur independently of, for example, storm surge associated with tropical storms, cool season coastal (extratropical) storms, and/or excessive rainfall.
While the D.C. area is looking at a future with more frequent flood events, possibly even 400 per year, Miami is on the front lines of dealing with the consequences of sea level rise right now. With huge financial assets and large population at risk, the region is facing the daunting challenge of mitigating what the future might bring. In advance of this week’s king tides, independent counties in southeast Florida have been exemplary in working cooperatively to install some (though not nearly enough) water pumps to reduce flooding and minimize brackish water from entering the aquifer that provides around 90 percent of Florida’s drinking water.
Miami is looking to younger generations to become familiar with and spread the word about issues concerning sea level rise. Fifty Florida International University college students and 20 Maritime and Science Technology Academy high school students are conducting hands-on experiments in the south beach area of Miami to measure the salinity, water quality, and depth of the flood water expected at high tides.
The Miami region’s efforts can serve as a model for other locations to identify the challenges of and deal with the threat of rising sea levels, and “do so together,” rather than as independent regional programs which overlap common specific challenges. Of course, that is if and only if they become concerned enough to act at all before it’s too late.