Hurricane Sandy

What Happened When 549 Imaginary Storms Hit New York

Damage following Hurricane Sandy, in Queens, New York, on Oct. 31, 2012

Photograph by Spencer Platt/Getty Images

Damage following Hurricane Sandy, in Queens, New York, on Oct. 31, 2012

How much would it cost to protect New York City from the next superstorm Sandy? To find out, researchers from the U.S. and Netherlands bashed the city with 549 simulations of storm surges, ranging from bad to “extremely low probability” (i.e., really bad). Then the researchers did a benefit-cost analysis of different defenses, including erecting massive surge barriers in lower New York Bay and the Long Island Sound.

The result? Surge barriers do have a positive payoff despite their enormous expense. But the more cost-effective option is to skip the barriers, allowing the floodwaters to surge into the city while protecting “critical infrastructure” near sea level, such as airports. The researchers also put forward the idea of paying for the fix with a “resilience fee” on visitors to New York.

sciencemag.orgThe study, published in the May 2 issue of Science, is by Jeroen Aerts of VU University in Amsterdam and Erwann Michel-Kerjan of the University of Pennsylvania’s Wharton School, along with co-authors from VU University, Massachusetts Institute of Technology, and Princeton University.

This first map shows the most extreme surge-barrier option. One stretches from Sandy Hook, N.J., northeast to the tip of the Rockaways in New York City, while the shorter one closes off the East River from waters rushing down the Long Island Sound. These barriers would be down most of the time to allow for ship traffic but would be put in place to combat surges. To make sure the floods don’t just go around the barriers, there would have to be levees erected on both sides. Essentially walling off all of the city would minimize the need for local protection of infrastructure. It’s cheaper to erect just these two outer walls than to have three or four barriers that are closer to the city. This option would cost somewhere between $11 billion and $15 billion, and a middle-range climate scenario would have benefits 2.24 times as high as costs, the study estimates.

sciencemag.orgThe second map shows a solution that the study concludes has a slightly higher payoff, with a cost of $10 billion to $12 billion and benefits 2.45 times as high as costs. In this “hybrid” plan, no surge barriers are at the outer limits of the city. Instead, building codes are tougher for low-lying parts of New York and New Jersey, together with protection of critical infrastructure, such as the airports, some levees, and what the authors call “moderate enhancement protection” along parts of the Manhattan and Brooklyn waterfronts.

Then comes the question of how to pay for all this. The study says that since New York City’s continued good health benefits the rest of the world, a case can be made for tapping the state and federal governments as well as domestic and foreign tourists: “For instance, with more than 50 million tourists visiting the city every year, a simple $10 resilience fee—equivalent to the maximum September 11 airline security fee [that] anyone traveling in the United States is now paying for a roundtrip ticket—could help.”

Coy is Bloomberg Businessweek's economics editor. His Twitter handle is @petercoy.

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