News•October 10, 2016

Sandy's Surge Was Extreme. It Could Become Normal

The destructive force of storm surge was on clear display this weekend as Hurricane Matthew ripped across the Caribbean, Florida and the Carolinas. For some in New York, it may have brought back memories of Sandy, another destructive October storm that broke flood records and upended the metropolitan area.

Research published on Monday in the Proceedings of the National Academy of Sciences shows that the risk posed by future storms like Sandy is only going to increase due to climate change. The potential for stronger storms and rising seas mean Sandy-level flooding could could occur once every 23 years as opposed to once every 400.

Storm surge damage from Sandy on Staten Island.
Credit: Somayya Ali Ibrahim

The results are specific to New York, but the methods could be applied anywhere in the Atlantic hurricane basin to show the rising risks of catastrophic flooding as the world warms.

Sandy has become a touchpoint for climate adaptation efforts in New York. The October 2012 storm generated the highest storm tide ever recorded in New York, reaching to nearly 14 feet in height, about 9 feet of which was from storm surge.

Overall, the storm caused $19 billion in damage in the region (and $50 billion in total for the U.S.), killed dozens and even shut down the Statue of Liberty and Ellis Island for a year. Planning for future flood events like Sandy is crucial for protecting the 8 million people that call New York home.

“Following Hurricane Sandy, New York has been making plans on risk mitigation strategies and building coastal defenses,” Ning Lin, an engineer at Princeton who led the study, said. “These designs would be more effective and economic if based on state-of-the-art climate projections. Our study provides such projections.”

Sea level rise played a major role in driving Sandy’s surge. Oceans have risen about foot in New York Harbor since the start of the 20th century.

Past research has shown that sea level rise has helped increase the odds of waters overtopping Manhattan’s defenses from once in every 100 to 400 years in the 19th century to once in every four to five years.

The trend has accelerated and is expected to keep doing so. In the new study, researchers at Princeton and Rutgers estimated that New York is likely to see 20 to 40 inches of sea level rise by the end of the century. That alone will make the risk of a Sandy-level storm surge increase to once every 90 years. (It should be noted that the results don’t mean a surge like that will happen like clockwork, but rather reflect the odds of a storm surge like that occurring in a given year.)

Add in the prospect of more intense hurricanes and the risk of that level of storm surge could be as high once every 23 years, raising the spectre of a Sandy-level storm every generation. Lin said the models they used for hurricanes aren’t totally in agreement about overall storm frequency, though they show intensity is likely to increase.

The surge heights of the current 400-year storm will also increase dramatically. Factoring in both more intense storms and sea level rise, the study suggests that storm surge could reach higher than 14 feet alone, equalling the total storm tide of Sandy.

The results come with a caveat. Researchers used a middle of the road climate scenario where nations start to rein in carbon pollution. Lin said they chose the scenario because it “may be realistic given hopefully that efforts will be made under the Paris Agreement.”

So the results are a carrot (or perhaps a stick) to get the world to move quickly to cut it carbon pollution. Otherwise sea levels could rise much higher, increasing the risk of storm surge even more. The results also present actionable information for New York, which is spending nearly $20 billion on climate resiliency and sustainability.

“This study advances the knowledge of how the frequency of coastal flooding in the New York City metropolitan area has changed in the past and is projected to change in the future,” Dan Bader, a program manager at the Consortium for Climate Risk in the Urban Northeast, said. “It adds to the existing local science already in use for resiliency planning and will help further improve preparedness in the coming decades.”

New York is hardly the only place that will be forced to reckon with sea level rise and the attendant risks of storm surge flooding. Last winter, storms battered the Mid-Atlantic and Hurricane Matthew is fresh on people’s minds after setting a high water mark in coastal Georgia and battering communities along Florida’s eastern coast.

Lin said the techniques used in this study could be easily replicated in those areas or anywhere along the Eastern Seaboard. With sea level rise likely to impact communities up and down the coast, they’re likely to come in handy.