Master Sgt. Mark C. Olsen/U.S. Air Force/New Jersey National Guard/Wikimedia Commons

New York City area could soon see massive floods every 5 years

This year’s Atlantic hurricane season was off the charts by nearly every measure, and new climate modeling suggests that New York City may be headed for weather that could make superstorm Sandy look routine. Flooding from hurricanes will intensify with sea level rise, and what was—in preindustrial times—a once-in-500-years flood may occur once every 5 years by 2030 scientists report today in the Proceedings of the National Academy of Sciences. The researchers used sediment cores from along the New Jersey shore to reconstruct flood events from 850 C.E. to modern times. Until 1800, flooding of 2.25 meters above sea level, slightly below Sandy’s 2.8-meter surge, took place on average once every 500 years. From 1970 to 2005, floods of that height had a probability of occurring once every 25 years. To project that trend forward, the team then used models recently developed to analyze Antarctic ice sheet collapse, plus large global data sets to tailor specific Atlantic tropical cyclone data and create “synthetic” storms to simulate future weather patterns. When combined with projected sea level rise, flooding of 2.25 meters—enough to do tens of billions of dollars of damage—could take place every 5 years from 2030 to 2045. And the definition of a once-in-500-years event will change as well, reaching as high as 5.1 meters by the end of this century and as high as 15.4 meters by the year 2300—enough to cover most of LaGuardia airport and all of Liberty Island. Of course, those numbers are the product of many assumptions, including partial collapse of the Antarctic ice sheet, and they are less reliable the further out they go. But if there’s any good news, it’s that the new study also indicates that future climate dynamics may drive Atlantic hurricanes farther offshore, potentially preventing the deadly compounding of sea level rise with storm surge increases, and possibly sparing New York City fewer Sandy-style direct hits.