Climate change increases risk of storm surges, according to MIT study

By Carolyn Y. Johnson, Globe Staff

Studies of climate change and its impact on coastal communities usually focus on rising sea level. Now, scientists from MIT and Princeton University have developed a method to examine how multiple effects of climate change – including the combination of sea-level rise and stronger hurricanes -- will affect storm surges that wash over sea walls and inundate communities, damaging buildings and infrastructure.

As a demonstration of the new technique, the scientists quantified how hurricane storm surges would affect New York City. They found that coupled with climate change, there would be a dramatic increase in the annual risk of so-called “100-year events” that have a 1 percent risk of occurring in any given year. As the climate changes, such powerful storms would have a 5 to 33 percent chance of happening in a given year in Manhattan, the scientists reported in an analysis published online today in the journal Nature Climate Change.

Kerry Emanuel, a professor of atmospheric sciences at MIT and an author of the paper, said that the method hasn’t been used to analyze Boston, but that because of Boston Harbor’s orientation and the characteristics of hurricanes that strike here, the city wasn’t particularly susceptible to hurricane storm surges. Narragansett Bay, on the other hand, is at greater risk.

“The technique could be applied anywhere,” Emanuel said. While it has become clear that climate change will have an impact on sea-level rise and hurricane intensity, Emanuel said that scientists have lacked tools to predict and quantify the combination of these effects.

The scientists used computer models, including four climate models and a hurricane model. They compared two time frames: storm activity and surges under present climate conditions from 1981 to 2000, and surges under the anticipated climate in 2081 to 2100.

The models predicted different rates of intense storms under the various climate scenarios, ranging from a 15 percent decrease in intense storms to a three-fold increase. Then, they used models to predict the storm surges expected in the various scenarios.

The scientists noted that even today, a “100-year storm” would cause a 6.5-foot storm surge, which would already rise above the sea wall protecting lower Manhattan. The sea level rise for New York City is predicted to be between 1.5 and 5 feet at the end of the century, and the researchers’ modeling predicted the increase in the storm surge level to be similar. Under the climate-change scenarios, the risk of such a “100-year storm” occurring or being exceeded would go from one percent a year to five percent a year or more.

“We lacked a good way of quantifying it, putting actual numbers on it ... ” Emanuel said. “This is a way of catching actual numbers, like how much would it increase; what’s the range of possible outcomes, and how do you factor in sea level rise.”