The incidence of major floods in the Big Apple has tripled since 1800, and it could more than quadruple over the next century.
By Nathan Collins
Taxis sit in a flooded lot after Hurricane Sandy hits. (Photo: Michael Bocchieri/Getty Images)
When Hurricane Sandy reached the Mid-Atlantic four years ago, it brought with it some of the most severe flooding the region has ever seen. It also took a financial toll, with damages totaling more than $71 billion—second only to Hurricane Katrina among damage in the United States. And here comes more bad news: Researchers report that New York City is likely to get hit by many more floods on par with Sandy in the future.
“[T]he frequency of Hurricane Sandy-like extreme flood events has increased significantly over the past two centuries and is very likely to increase more sharply over the 21st century, due to the compound effects of sea level rise and storm climatology change,” Ning Lin, an assistant professor of civil and environmental engineering at Princeton University, and her colleagues write today in Proceedings of the National Academy of Sciences.
Estimating the future of flooding is not an easy task, in part because so many factors go into determining the severity of any given flood. To start off, the researchers used sea-level data measured at the Battery in New York City and other locations along the Mid-Atlantic coast. They combined this data with a model of hurricane size, intensity, and trajectory; and a model of storm surges based on data from the National Centers for Environmental Prediction.
Flooding on par with Hurricane Sandy could hit New York as often as once every 23 years.
Based on that analysis, the team estimates that, given sea levels in the year 1800, Sandy-level surges—about 10 feet above ordinary sea level—would have occurred on average once every 1,200 years. By 2000, average sea level rose enough to make that number once every 400 years; by 2100, the authors project sea levels will make Sandy-like storms 90-year events.
Those projections, however, only take into account projected sea level rises, and ignore the potential effects of climate change on hurricanes and their relationship to storm surges. Using four standard global climate models, the researchers estimate that flooding on par with Hurricane Sandy could hit New York as often as once every 23 years.
There are some important limitations to the study, the authors point out. Notably, global climate models are not designed to provide precise estimates of the weather in any given location or in any given year, so there are substantial uncertainties when it comes to predicting hurricanes and sea level rise in New York City. Indeed, the four climate models’ predictions ranged from 23 years to 130 years, and more needs to be done to improve those predictions.
But, despite those caveats, the “results of this analysis demonstrate how dramatically the frequency and magnitude of NYC’s extreme floods may increase over time, due to the compound effects of sea level rise and storm climatology change,” the authors write.
