PNAS Study: Expect 500-Year Floods In NYC Every Five Years; Oh, And Elevate Everything 3 Feet

Climate change is dramatically increasing the risk of severe flooding from hurricanes in New York City, to the extent that what was a once-in-500-years flood when the city was founded could be expected every five years within a couple of decades. Throughout the century, of course, the risk of flooding increases as sea levels are expected to continue to rise.

These are the findings of a study published today that modeled how climate change may affect flooding from tropical cyclones in the city. The increased risk, the authors found, was largely due to sea level rise. While storms are expected to grow stronger as the planet warms, models project that they'll turn farther out to sea, with fewer making direct hits on New York. However, when sea level rise is added into the picture, "it becomes clear that flood heights will become much worse in the future," said Andra J. Garner, a postdoctoral researcher at Rutgers University and the lead author of the study.

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To put that in perspective, New York City's subway system starts to flood at about 10.5 feet above the average low water mark, as the city saw during Hurricane Sandy five years ago, and Kennedy Airport is only about 14 feet above sea level. "If we want to plan for future risk, we don't want to ignore potential worst case scenarios," Garner said.

In May, the city published guidelines for builders and engineers recommending that they add 16 inches to whatever current code requires for elevating structures that are expected to last until 2040, and 3 feet to anything expected to be around through 2100. That falls in the lower half of the range projected by the new study. By the end of the century, it says, the flooding from a once-in-500-years storm could be anywhere from about 2 feet to 5.6 feet higher than today.

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https://insideclimatenews.org/news/23102017/nyc-sea-level-storm-surge-climate-change-building-codes-sandy