For the fifth year in a row, Norfolk takes the top spot for sea-level rise on the East Coast
The city of Norfolk holds onto its mantle among East Coast cities most threatened by sea level rise, according to a new study.
In March, the Virginia Institute of Marine Science at William & Mary released its latest Sea-Level Report Cards. According to VIMS, Norfolk has a rise rate of 5.38 millimeters (.212 inches) per year, making it the highest rate on the East Coast for a fifth year in a row. The report looked at areas across the country, including the West, Alaska and Gulf Coast, and forecasts sea levels up to the year 2050 based on an annual analysis of tide-gauge records for 32 localities along the U.S. coastlines.
Molly Mitchell, research assistant professor for VIMS, said Norfolk is seeing more flooding than decades ago. Though the city is sinking, Mitchell said, it is at a slower rate than locales along the Gulf Coast. Grand Isle, Louisiana, has the highest rate, topping out at more than 8 millimeters (.315 inches) per year.
Sandy Hook, New Jersey, took second place on the East Coast and had a rise rate of 4.47 millimeters (.176 inches), followed by Savannah, Georgia. Mitchell said over the past five years, the Carolinas have seen a more significant acceleration in rise rates, though they’re still behind Norfolk overall.
“It’s important as we look in the future, to know that if something like absolutely cannot get wet, we need to build in a little margin of safety for it over the sea-level rise curves, because we know there are years where it’ll run high and above those curves,” she said.
Most global climate models predict a rise in absolute sea level — an increase in seawater mass because of melting land ice or an increase in volume due to thermal expansion. VIMS’s report cards forecast changes in relative sea level — the height of water relative to the land surface on which people live.
“In areas like Norfolk, land subsidence due to groundwater withdrawal and other factors magnifies the rise in absolute sea level, compounding the frequency and severity of coastal flooding,” the report reads.
The report also includes extremes to represent highs and lows in predictions. Mitchell said this portion of the report shows good and bad years.
“We project that mean sea level in Norfolk will rise 1.5 feet by 2050. But what planners and property owners really care about are the likely extremes,” the report reads. “The bottom line: the safest planning level for 2050 is a 2.1-foot rise in sea level—not the 1-foot rise projected from a linear extrapolation.”
Mitchell said the in short term, there will be years where the levels are higher than others, and some where they may be lower, so including extremes in the report allows for local leaders, planners and homeowners to see the upper end of predictions. According to the graph, by July 2030, the upper prediction for Norfolk would be about 1.31 feet, and the lower prediction would be about 0.4 feet.
“Those bounds are showing us, in the future, that the amount of variability we expect on a monthly and inter-annual basis. So we can see where we think our mean sea level will be,” Mitchell said. “But we can also see in our worst-case year, the flooding is going to be at (a 2.1-foot rise by 2050). So it also gives us that ability to look at it and say, ‘Okay, so in a really bad year, how much more flooding do we expect to see?’”
