Stonington — A panel of experts on climate science and adaption to the rise of sea levels painted a grim picture for people living along the shoreline or rivers Wednesday night, warning those who live in or near flood zones that flooding in their house and on roads is a matter of "when," not "if."

The three experts spoke at the La Grua Center Wednesday night at an event titled "Coastal Resiliency: Now More Than Ever," outlining Connecticut's risk of damage from more extreme and frequent hurricanes and storms. It was co-sponsored by Mystic Aquarium.  

"The potential for a major hurricane basically destroying the tree canopy and the infrastructure is very, very real," said David Vallee, a hydrologist with the National Weather Service’s Northeast River Forecast Center.

"For those of you who lived here through (Hurricane) Irene, you may recall power was out in parts of eastern Connecticut and Rhode Island for more than seven days," Vallee said.

The damage from that hurricane, which only hit Connecticut as a tropical storm, destroyed homes and left half the state without power. But, Vallee said, Irene pales in comparison to a truly vicious hurricane, which Connecticut has not seen since Hurricane Carol smashed into the shoreline in 1954.

Efforts to elevate homes above predicted flooding levels have still proved more popular than abandoning buildings at high risk of flooding, said Juliana Barrett, a scientist at the University of Connecticut Sea Grant College Program and the Department of Extension.

"People arent quite ready to talk about retreat from the shoreline, and so we're elevating," she said.

And for those in a state-mandated hurricane evacuation zone, Vallee said, even elevated houses won't necessarily protect homeowners.

"If the roads are flooded, having a house above the water line won't make much difference," Vallee said. "Your evacuation zone isn't necessarily about your property getting wet — it accounts for roads getting washed out or flooded."

Vallee spoke after Jim O’Donnell, the executive director of the Connecticut Institute for Resilience and Climate Adaptation (CIRCA), showed a nearly full audience graphs showing the uncertain future of rising water levels.

"There's things we know, and there's things were not sure about," O'Donnell said.

But to be safe, he recommended that government officials in Connecticut plan for the high end of the possible impact of rising carbon dioxide levels in the Earth's atmosphere.

"Start planning for sea levels by 2050 that's 50 centimeters higher than it is now," he said.

That possibility is not just bad because more storms with wind could knock down trees and power lines, Vallee said, but also because storms in New England tend to move slowly and dump a lot of rain, causing flooding up and down waterways that run inland from the coast.

"It's not just about the warming climate," Vallee said. "It's the warming climate and the atmosphere producing more high-level precipitation events."

Barrett, whose work at UConn focuses on climate adaptation and resilience, detailed efforts to reverse erosion on Connecticut beaches that has resulted from storms and higher tides, incuding work at Dodge Paddock and Beal Preserve, a tract of land on the other side of Stonington Borough, a few hundred yards from the La Grua Center.

But much of New England's infrastructure — like sewer systems, water reservoirs and roads, weren't built for the amount of rain that multiple storms resembling Hurricane Carol could soon be inflicting on Connecticut.

"The infrastructure was designed for the way it rained in the 1950s," Vallee said. "They simply haven't been designed for the amount of water that Mother Nature is dropping on us."

m.shanahan@theday.com