500 Year Floods Now Coming To New York Every 24 Years

500 Year Floods Now Coming To New York Every 24 Years

Bad news for New Yorkers: The inundation of Hurricane Sandy might have been billed as a 3,000 year flood, but according to new research, the recurrence interval for Sandy-sized flood events has shrunk. By a factor of 23.

We already knew that New York City was on the front lines of sea level rise, but research published this week in the Proceedings of the National Academies of Science finds that the Big Apple has also become a lot more susceptible to inundation from massive storms. Historic records of flooding in New York only date back to the mid-19th century, but by examining the distribution of microfossils called foraminifera in nearby salt marshes, researchers were able to reconstruct the history of tropical cyclones and flood events all the way back to 850 AD.

Their findings? Modern times are getting weird. Focusing on the neighbourhood in Lower Manhattan known as the Battery, the researchers found that while a Sandy-sized storm — which produced 9.2 feet (2.81 meters) of surge — used to be a 3,000 year event, a flood of its magnitude could now occur every 130 years. 500 year floods, which cause 7.4 feet (2.25 meters) of storm surge, are now predicted to smack Manhattan ever 24 years. New Yorkers can thank a combination of sea level rise and more extreme storm events for their flood-filled future.

What’s the city to do about this sorry forecast? First off, New York needs to start investing in storm-proof infrastructure, whether that means higher seawalls, sturdier building foundations or new outflows for waterlogged streets. Second, its 8 million-ish voters could, you know, start using their political weight to help elect candidates who actually want to tackle climate change — which is, of course, the undisputed root of the problem.

If they don’t like either of those options? Buy a kayak.

[Read the full scientific paper at PNAS h/t New Scientist]

Top image: Sea water floods the Ground Zero construction site, Monday, Oct. 29, in Manhattan, via John Minchillo / AP