When Hurricane Sandy sent water crashing over the seawall at Battery Park in lower Manhattan in October 2012, water flooded the 9/11 memorial and the subway. This storm surge set a new and dangerous trend. Although Sandy’s storm tide was unprecedented, it is unlikely it will stay that way.
Sea level rise and a newly discovered increase in the height of storm tides in New York Harbor mean that the odds of the Manhattan seawall being overtopped are on the rise. Using recently rediscovered archival measurements of tide height, Talke et al. found that the odds of the seawall’s 1.75-meter height being breached in a given year were just 1% in the mid-19th century. Today, those same odds stand at 20% to 25%.
Tide gauges have been continuously recording the sea level in New York Harbor since 1844, but until recently, many of these records were largely inaccessible. As part of previous work, the authors rediscovered and digitized these 19th century data from paper logs that had been housed in the U.S. National Archives. Using this extended observational record, the authors calculated trends in storm tides and storm surge.
Since 1856, the average sea level in New York Harbor has increased by 0.44 meters, previous research has shown. Building on that discovery, the authors found that there has been an additional increase of 0.28 meters in the 10-year storm tide height. The increases in sea level height and storm tide height combine so that 3 of the top 9 recorded water levels in New York Harbor have occurred since 2010 and 8 of the top 20 have occurred since 1990. These changes have had a huge effect on the ability of the seawall to keep Manhattan dry.
As the authors note, the cause of the increasing storm tides remains unknown: it could stem from the destruction of wetlands and dredging of waterways or from shifting storm tracks and increasing strength due to climate change. (Geophysical Research Letters, doi:10.1002/2014GL059574, 2014)
—Colin Schultz, Writer
Citation: Schultz, C. (2014), Flood risk from storm surge is increasing in New York, Eos, 95, doi:10.1029/2014EO021399.