Floods that were as intense as Hurricane Sandy in the New York City area are at least three to as much as seventeen times more likely to occur over the next century, according to new research just published in the journal Proceedings of the National Academy of Sciences.

Hurricane Sandy bearing down on the Middle Atlantic coast in 2012.

The research team with members from Rutgers University, Princeton University and the Woods Hole Oceanographic Institution used a combination of historical records such as tidal gauge and geological data from the New York City area along with computer model projections to reach their conclusion.

The primary reason for this predicted increase in flood risk is due to the projected acceleration of sea level rise through the end of the century.

Key excerpts from the News at Princeton.... and Rutgers Today.

“The grand answer is that things are going to get worse by 2100,” says Benjamin Horton, who is professor of Marine and Coastal Sciences in the School of Environmental and Biological Sciences. “If nothing changes with hurricanes, sea-level rise alone will increase the frequency of Sandy-like events by 2100.”

The researchers noted that every Sandy-sized storm surge doesn't necessarily equate to flooding like that seen during Sandy, which also happened to hit during a particularly high astronomical tide (the tide due to the gravitational pull of Earth’s moon). The summation of the storm surge and the astronomical tide is called the “storm tide," the total height of the floodwaters. A hurricane that produced the same size storm surge as Sandy, but that peaked during a low astronomical tide, might not cause the same catastrophic flooding. “The effect of astronomical tide will be accounted for in the future,” said Ning Lin, the lead author of the paper and a Princeton assistant professor of civil and environmental engineering “but the tide component doesn’t change with the climate and so the increasing trend of flood frequency will be similar.”

There is still much debate about whether hurricanes are becoming more frequent and intense. "But even if storms occur at the same frequency and strength, our estimates suggest the frequency of surge floods will significantly increase based on rising sea level,” said Lin.

“We ask, ‘What is likely?’ and ‘What are the extremes?’" said Robert Kopp of Rutgers University. "We take into account factors that cause local sea level to vary from global sea level. And we’ve shown, through geological investigations, that our projections are consistent with the assumption that temperature and sea level will be related in the future as they have been over the past two thousand years.”

Projections are not predictions and, Horton says, the spread between what “likely” and “extreme” is an indication of the complexity of future projection. “Things are only going to get worse by 2100,” Horton says. “It’s just a question of how much worse it will get. There is no happy scenario.”

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