Despite tranquil weather to start this week, flooding has affected coastal communities in the United States from the Florida Keys to Maine. Long stretches of shoreline along the East Coast were inundated, water levels running a foot or more above normal. The swollen sea temporarily claimed streets, parking lots and public parks, and even seeped into homes, reminiscent of a storm surge.
But there was no storm to be found. In fact, many places enjoyed pleasant weather and sunshine. Yet coastal flood advisories plastered the coast, forcing road closures and flooding properties.
The culprit? King tides. A name informally attached to extra-high tides spurred by astronomical alignments, king tides often reach their peak in the fall. Decades ago, their impact was minimal. But added to the background of climate-driven sea-level rise, nowadays they are routinely problematic.
I think of this like a stacking of phenomena, said William Sweet, an oceanographer with NOAA specializing in sea-level rise and flooding issues. We didn’t flood 30 or 40 years ago, but since then sea levels have been a half-foot to a foot higher.
The rise in water has left thousands of homes and businesses vulnerable to sunny-day flooding, disrupting daily life and undermining property values in some areas.
As greenhouse gases resulting from human activity continue to accumulate in the atmosphere and warm the climate, sea-level rise and coastal inundation will only continue to grow with time, even on sunny days.
October is typically the worst month for king tide flooding, with some of the highest water levels of the year.
King tides are the highest tides that occur and are easily predictable based on the orbits of the sun and the moon. Both celestial bodies exert a gravitational pull on the oceans, helping generate tides. The closer either body, the greater the tide.
King tides are a natural phenomenon, but added to the background of rising seas, their impact and disruptive potential is growing exponentially. In Miami, for example, a roughly six-inch increase in sea level since 1996 has led to a twelvefold spike in action-tier flooding.