Sea level rise causing huge increases in “nuisance flooding”

A northeaster—a common type of storm on the East Coast—causes severe flooding in Virginia.

Virginia Sea Grant

The warming of the planet is driving ocean levels upward through two processes: the melting of land-based ice and the thermal expansion of the water in the oceans. Due to the vast energies involved, both of these processes are slow, so the ocean levels have only been creeping up a few millimeters a year. That slow pace makes it difficult for anyone to perceive the changes.

But it's clear that those changes are taking place. In the latest indication, the National Oceanic and Atmospheric Administration (NOAA) has compiled data on what it calls "nuisance floods," cases where coastal communities have to deal with flooding as a result of high tides or minor storms. Over the last 50 years, instances of these floods along the East Coast have gone up by anywhere from 300 to 900 percent.

On the rare occasions where sea level rise reaches the public's consciousness, it's typically as a result of a catastrophic event like Hurricane Sandy. Sea level rise does exacerbate these events, as the flooding reaches higher levels and extends over a wider area than it would have a century earlier. But the rarity and magnitude of catastrophes like these make it difficult for people to associate them with a gradual process. At the same time, the immediate effect of the process itself—high tides being about an inch higher every decade—is difficult for humans to perceive. As NOAA's new report puts it, "neither changes in tidal datum elevations nor rare-event probabilities are readily apparent to the casual observer."