Read the original story in The Oregonian here.
Imagine a camera set up on 42nd Street in Manhattan from 1852 through today—a camera that snapped a photograph every hour of every day for 152 years and the amazing changes it would show.
That's tantamount to what Stefan Talke, an assistant professor of civil and environmental engineering at Portland State University, discovered when he started researching tides and storm-tides for Astoria.
That research led him to tides and storm-tides data for New York Harbor and a new study authored by Talke, his colleague David Jay, and Philip Orton of the Stevens Institute of Technology, called "Increasing Storm Tides in New York Harbor, 1844-2013," accepted for publication in the American Geophysical Union's journal, "Geophysical Research Letters."
What the study found is that the storm tide created by Hurricane Sandy was the largest since 1821, and that New York is "at risk of more frequent and extensive flooding than was expected due to sea-level rise alone," Talke said.
Talke and his colleagues also found that the risk for water overtopping the Manhattan seawall is now 20 times greater than it was 170 years ago due to a 2.5 feet rise in water levels during major storms.
How did a study of Astoria tides lead to ground-breaking research on tides and storm tides in New York City?
In 2010, Talke contacted officials at the National Oceanic and Atmospheric Administration (NOAA) and told them he was looking for historic tide and storm tide data for Astoria. NOAA told him what they told other researchers before him: they did not have such data.
But Talke kept at it. He flew to D.C. and showed up at NOAA's doorstep: "I'm here, he said, and I'm looking for old tide data from Astoria."
Finally, an old-timer at the agency found some boxes in a storage room that contained Astoria data from 1853 to 1876. During his research, Talke discovered dozens of binders that cataloged all the data that the National Ocean Service (a division of NOAA) had ever collected, including additional tide data from the 1800s from all over the United States.
With the help of archivists, Talke found that these records had recently been moved from a federal archive to the U.S. National Archives.
"I needed tide data, and I needed old tide data,'' Talke explained. "I found out that there was a lot of 20th century data missing. Then I found hints of an even earlier generation of data."
During a trip to New York in August 2012, co-author Philip Orton of the Stevens Institute of Technology got wind of what Talke was researching and asked him to look for any New York Harbor tide and storm-tide data and take some pictures of those, too.
Talke was floored by what he found.
"There were hundreds of station years of data that for all intent and purposes were forgotten," Talke said.
Two months later, Hurricane Sandy smashed into the East Coast, flooding lower sections of the city and overtopping the seawalls of New York Harbor. Suddenly, the value of the data became that much more important, he said.
Graduate student Patrick Lau was dispatched to the archives where he looked through the boxes from New York and New Jersey and took thousands of photographs. Back at PSU, a team of undergraduate and graduate students entered approximately 500,000 data points into spread sheets, nearly doubling the amount of available tide and storm-tide data for New York Harbor going back 170 years.
Up to that point, the data set available only went back to the 1920s—too short a time period to show long-term climate trends and fluctuations.
The earliest tide data was collected each day in the mid-19th Century by an observer who went out and read the water levels off a simple tide gauge, a staff in the mud very much like a yard stick.
In 1852, an automatic tide gauge was installed. A float in the automatic gauge was connected to a pencil, which moved up on down on a scroll of paper that unscrolled using a clock mechanism.
"As the paper moved you got a continuous trace of the tides," Talke said. "It is as if you had a camera on a street corner in New York and you took a picture every hour for the last 150 years. It nearly doubled the available amount of tide data."
The study found that a major 10-year storm would cause much more damage now than it would have in the mid-1800s. A 10-year storm tide today would reach a height of 6.5 feet above sea level, about a foot higher than it would have reached in 1844.
The study also found that in the 19th century, storm-tides were only expected to overtop the seawall once every 100 to 400 years. Now that figure is closer to once every 4 to 5 years.
"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 told the AGU.
Talke attributes part of the dramatic shift to rising sea levels caused by local land subsidence and global warming. On top of that, storm surge and storm tides are getting larger, possibly due to increasing storm strength.
Other causes might be connected to more localized reasons such as the dredging of nearby shipping channels and the loss of wetlands, which changes the way storm surge flows into the harbor.
In addition to finding a long-term trend, the study found that the North Atlantic Oscillation, an irregular fluctuation of atmospheric pressure over the North Atlantic Ocean, affects storm tide heights. Those pressure fluctuations strongly influence winter weather in the Northeastern U.S., as well as Greenland, Europe, North Africa and northern Asia.
Having access to the data from a relatively long time span should help scientists and city officials make better predictions about the impact of future storms and how to mitigate the potential damage.
"If it turns out to be a local reason, as has been suggested in some cases, there could be local solutions as well," Talke told the AGU. "In some cases, we may be able to turn back the clock on that a bit."