GOWANUS, BROOKLYN—Superstorm Sandy's surge halted a little more than a block from my home, mirroring almost precisely the border of two different nearby flood zones on New York City's evacuation map. Homes, stores and warehouses closer to the Gowanus Canal at the westernmost end of Long Island—one of the most polluted sites in the U.S. as a result of an industrial legacy paired with sewage overflows in heavy rains, qualifying its bottom muck, waters and adjacent land for Superfund designation—saw basements and lower floors turned into stinking pools. The foul waters remained trapped by sandbags and other would-be antiflood precautions even the day after.
Throughout the New York metropolitan region and farther south in New Jersey, Sandy's hurricane-force winds brought down trees and power lines, causing an estimated $20 billion or more in damage. But the more than 74-mile-per-hour winds’ most enduring impact may have been from the massive swell of water they pushed atop land, obliterating beaches, drowning boardwalks, filling subway tunnels, destroying electrical infrastructure and wrecking lives.
Although it may be hard to believe, the event could have been even more damaging. "This was not the worst case," says storm surge specialist Jamie Rhome of the National Hurricane Center (NHC) at the U.S. National Oceanic and Atmospheric Administration. "A worst case would have been a stronger storm with the exact same track" that also came ashore at the same time as high tide. "That would have produced even more flooding," he adds.
Yet, Superstorm Sandy's massive flooding is already unprecedented in recent decades. According to experts, however, it is only going to become more likely in coming decades, thanks to a combination of local geography, vulnerable coastal development and already-happening sea-level rise as a result of climate change. In the future, it will not take a frankenstorm like Sandy to inundate the region. Given that reality, the best defense may be to accept the inevitability of flooding and prepare infrastructure to withstand it, as is common in other regions more historically prone to storm surge flooding.
Not the first flood
The New York metropolitan area has, of course, suffered damaging storm surges throughout its history, although most were not as severe. For example, in 1960 Hurricane Donna stormed up the entire Eastern seaboard as a Category 2 tropical cyclone, boasting winds above 105 mph. Even though Donna had mitigating factors—it arrived at low tide and that storm (like last year’s Category 1 Hurricane Irene) traveled parallel to the coast rather than striking it head on—those winds pushed enough seawater into New York Harbor to cause a storm surge of more than six feet that similarly inundated parts of Manhattan.
In contrast, Sandy's larger surge is a result of the post-tropical cyclone's track, which saw the superstorm turn in to and then smash the coast of New Jersey, pushing a punishing wall of water in front of it into the Garden State’s coast as well as north into New York Harbor.
How do winds create a storm surge? In a tropical cyclone, air pressure is highest at the edges and low at the center. The air flows, at speeds above 74 mph, to fill that low-pressure area. In addition, the low pressure itself helps raise the sea's level beneath it, heightening the surge where the center of the storm makes landfall. Wave action itself can also enhance the effect, adding even more height to a storm surge as the waves pile into shore one on top of the next.