New York City is likely to experience more flooding in the future, according to a forthcoming study of storm tide data. Climate change is at least partly to blame for the problem, as it makes New York more flood prone, with serious floods likely to happen every four or five years now.
The new study of flood risk in the city predicted that water would come over the seawall every four or five years, in contract to the 100-400 year time-frame estimated in the mid-19th century. The city is 20 times more likely to flood than it was 170 years ago. Sea level has risen since then, and storms have become more common.
Researchers at Portland State University and Stevens Institute of Technology looked at storm tides affecting the city. A storm tide is the amount that water levels rise during a storm, including both the storm surge and the effect of tides. Any storm over the ocean near New York City can tend to push water toward the city.
New York City could see more scenarios similar to the aftermath of Hurricane Sandy, where the storm tide peaked at 14.06 feet, enough to flood Battery Park. This was the highest storm tide recorded since 1821.
While much of the city is protected by a seawall, that protection is going to prove increasingly inadequate. Lower Manhattan has a 1.75 meter (5.74 feet) seawall, dating back to the middle of the 19th century. When built the seawall was able to protect the area from most storm surges, including so-called 10-year storms where the storm surge could reach top five feet. These events, driven in part by climate change, suggest that New York will be more prone to flooding.
A “ten-year storm” has a 10 percent chance per year of happening. Could hit the city with a two-meter storm surge, where 10 year storms in the middle of the 19th century only reached about 1.7 meters. The 10-year storm of long ago is not the same as a 10-year storm today, according to Stefan Talke of Portland State University, lead author of the study.
Talke and his fellow researchers studied tide gauge information taken from notes dating back to 1844. The researchers noted that three of the nine highest water levels happened since 2010. Eight of the 20 highest water levels have occurred since 1990. Storm tides have been a major contributor to this trend, the authors found. The storm tides have increased about a foot since tide tracking began in 1844.
Climate change and the associated changes in the climate are to blame, at least in part. The North Atlantic Oscillator, an ocean current that influences winter weather in Europe, Greenland, northeastern North America and North Africa has also contributed through variations in the strength of the current.
Climate scientist Radley Hurton of the Northeast Climate Science Center and NASA’s Goddard Institute for Space Studies said that the study highlights the fact that rising sea levels have increased the frequency and intensity of coastal flooding and suggest that storms may have gotten stronger. He did add that it is not clear how storms will be influenced by climate change.
Talke said that local factors like deepening of the shipping lanes around New York harbor could also be affecting storm tides. The channel between Sandy Hook, NJ and Raritan Bay was 24 feet deep in the 1800s, but was dredged out to accommodate huge new cruise ships and container ships. New York City has also lost 85 percent of the wetlands that would have blunted the impact of a storm surge.
New York is not the only city that climate change will make more flood-prone. The forthcoming study merely quantifies the risk to one of the North America’s largest city.
By Chester Davis