Sandy’s Effects on NYC Predicted by Two Recent Studies

E. B. White wrote, “It is a miracle that New York works at all. By rights New York should have destroyed itself long ago, from panic or fire or rioting or failure of some vital supply line in its circulatory system.” On Monday, Hurricane Sandy managed to cut off many of New York’s supply lines in ways they’ve never been tested before. The city lost power, water, and lives. But it was not only White’s fears, but also the predictions of scientists that were realized. Two separate papers, published earlier this year and last, predicted what would happen to New York City if it were struck by a severe storm.

In 2011, a state agency assembled a massive report on climate change in New York. In it, Klaus H. Jacob, a climate scientist at Columbia University’s Lamont-Doherty Earth Observatory, conducted a case study (PDF) on the impact of a 100-year flood on New York City’s transportation system. A 100-year flood is a flood whose severity, on average, is seen only once every hundred years (or has a 1 percent chance of occurring in any given year), which the study equates with a category 1 to 2 hurricane. Jacob looked at three scenarios: a 100-year flood alone, one combined with a 2-foot sea level rise, and another with a 4-foot sea level rise as a result of climate change.

Virtually all the subway lines in lower Manhattan and the tunnels under the East River would be flooded under the worst-case scenario, which indeed closely mimicked reality. (Jacob, 2011)

Jacob identified the areas that would be flooded under each scenario. Using a base flood elevation map of the city as well as known elevations of transportation structures, he found that low-lying streets, subways, and tunnels in the Battery, Jamaica Bay, the Rockaways and other neighborhoods near the city’s shoreline would be particularly vulnerable to flooding. Indeed, those areas were among those that suffered most from Hurricane Sandy. In fact, a record 14 feet, or 4.25 meters, of water swept over the Battery on Monday, matching the case study’s worst-case scenario. Jacob also predicted that the total economic and physical damages for NYC would be $58 billion, $70 billion, and $84 billion in order of worsening scenario. One current estimate stands at $20 billion in losses for the entire Northeast and Mid-Atlantic due to Sandy, so Jacob’s estimates seem to have overshot it. One thing is for sure though. Investing in infrastructure that protect the city from future storms can save money in the long run. As Jacob told New York Magazine, “For every dollar that you spend today, you probably save $4 of not incurred costs later.”

Just months after Jacob’s case study, Ning Lin, a climate scientist at MIT, and colleagues used computer models to predict the impact of a hurricane on New York City. Published in Nature Climate Change in February this year, the study used four climate models to simulate 10,000 synthetic storms, half under the current climate and half under projected warming conditions. The researchers programmed the storm to be within a 200-km radius from the Battery and to gust at wind speeds greater than 20 m/s, or 45 mph (Hurricane Sandy exceeded the models, with 60 mph recorded at Central Park). They found that in the worst-case scenarios, a hurricane would cause a storm surge as high as 4.57 m to 4.75 m at the Battery, which came fairly close to the 4.25 m caused by Sandy.

Two worst-case scenarios estimate surge height at the Battery to range from 4.75 m (left) to 4.57 m (right), coming fairly close to the 4.25 m record surge caused by Hurricane Sandy. (Lin, et al. 2012)

The researchers also found that climate change will only increase the risk of storm surges for the city. Based on historical data on NY-region storms, they predicted that a 1 m rise in sea level in the future will increase the likelihood of a 100-year surge flood occurring as frequently as every 3-20 years and a 500-year flood every 25-240 years by the end of the century. Of course, predicting something as unpredictable as a hurricane is extremely difficult. But the fact that the climate models closely mirrored Hurricane Sandy makes the need to prepare for future severe weather all the more urgent.