From: ClickGreen staff, ClickGreen, More from this Affiliate
Published April 23, 2014 03:05 PM

Odds of storm waters flooding Manhattan up 20-fold, new study finds

Maximum water levels in New York harbor during major storms have risen by nearly two and a half feet since the mid-1800s, making the chances of water overtopping the Manhattan seawall now at least 20 times greater than they were 170 years ago, according to a new study.

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Whereas sea-level rise, which is occurring globally, has raised water levels along New York harbor by nearly a foot and a half since the mid-19th century, the research shows that the maximum height of the city's "once-in-10-years" storm tide has grown additionally by almost a foot in that same period.

The newly recognized storm-tide increase means that New York is at risk of more frequent and extensive flooding than was expected due to sea-level rise alone, said Stefan Talke, an assistant professor of civil and environmental engineering at Portland State University in Portland, Oregon.

He is lead author of the new study accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union. The research also confirms that the New York harbor storm tide produced by Hurricane Sandy was the largest since at least 1821.

Tide gauge data analyzed in the study show that a major, "10-year" storm hitting New York City today causes bigger storm tides and potentially more damage than the identical storm would have in the mid-1800s.

Specifically, Talke explained, there's a 10 percent chance today that, in any given year, a storm tide in New York harbor will reach a maximum height of nearly two meters (about six and a half feet), the so-called "10-year storm." In the mid-19th century, however, that maximum height was about 1.7 meters (about 5.6 feet), or nearly a foot lower than it is today, according to tide gauge data going back to 1844, he noted.

"What we are finding is that the 10-year storm tide of your great-, great-grandparents is not the same as the 10-year storm tide of today," Talke said.

To get the data used in the study, Talke and a graduate student photographed hundreds of pages of handwritten hourly and daily tide gauge data going back to 1844 that is stored at the US National Archives in College Park, Md.

Talke and his students entered the data into spreadsheets and adjusted the data where points were erroneous or missing, including using newspaper accounts of big storms to fill in some of the holes.

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