Whether or not climate change leads to an increase in big hurricanes, one destructive effect of global warming is already at work in coastal Virginia — rising sea levels.

As sea levels go up, flooding from even low-level storms will become more destructive, scientists say.

“At times I think we get too locked in on the strongest storms, the Category 3, 4 and 5s,” said Marshall Shepherd, a University of Georgia atmospheric scientist. “But if you look at the last five or 10 years, even the weaker storms can create a lot more damage.”

Hurricane Isabel is a perfect example of this growing threat. To understand this, we need to look first at another storm.

The worst hurricane to hit southeastern Virginia in modern times was a 1933 storm whose center rolled northwest directly over Norfolk. It was a Category 1 hurricane, with winds reported at nearly 90 mph.

Called the Chesapeake-Potomac hurricane, the legendary storm pushed up record high tides along the west side of the Chesapeake Bay, “with damages the highest ever recorded from a storm surge,” according to the state Department of Emergency Management website. Eighteen people died.

Isabel in 2003, the center of which traveled northwest through central Virginia, weakened from a hurricane to a tropical storm about the time it hit the state, but it still caused $1.6 billion in damage, destroying homes, piers and other structures and contributing to more than 30 deaths in the state.

While less powerful overall than the ’33 hurricane, Isabel caused similar flooding because the sea level had risen 9 to 10 inches in the years between the two storms, scientists said.

That gave Isabel extra destructive power, enabling it to push its storm surge inland on higher waters.

As sea levels continue to rise, bad coastal flooding should get more common, said Larry P. Atkinson, an Old Dominion University oceanographer.

“What statistically happened every 100 years will happen every 80, then 50, then 20 and so on,” Atkinson said.

Sea-level rise is caused at least in part by global warming, because warm water expands. In Virginia, sea levels are rising faster than the global average because the land is sinking, primarily from natural causes.

For thousands of years, the sea level in Virginia went up about a foot a century. At least partly because of global warming, experts say, that rate increased during the 20th century, and waters are rising now at about a 2-feet-a-century clip. And some scientists say there’s evidence that sea levels will rise faster and faster in coming decades.

Celia and Jim Sease have a house along Mobjack Bay in low-lying Mathews County. Floodwaters from Isabel lapped at a door of their home, and the storm “pretty much destroyed” a nearby vacation rental house they owned at the time, flooding it with about 2 feet of water, Celia Sease said.

Sease said she can’t detect the rising sea level, but she has noticed an apparent increase in flooding in recent years. “I don’t know what the reason is. … It just seems like there’s a lot more flooding now from just normal rains.”

Flooding is indeed getting worse in coastal Virginia, said a January report from the Virginia Institute of Marine Science.

For example, a low-lying Norfolk neighborhood called the Hague, which flooded fewer than 25 hours a year in the late 1920s, flooded 200 to 300 hours a year in the mid- to late 2000s.

Also, people continue to build near Virginia’s coast, putting themselves and their property at risk.

Doug Dwoyer, a former NASA manager who lectures on climate change, said that coastal buildup means “economic damage from hurricanes will continue to increase even without increases in hurricane strength and/or frequency.”

Hurricane Isabel | 10 years later

Waterfront community rebuilds after Isabel

rspringston@timesdispatch.com

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