The East Coast of the U.S. is experiencing "sunny day flooding" that scientists didn't expect for decades yet.
Sea levels are rising at a rate of about an inch per year (5 inches from 2011-15) in some areas along the East Coast, from North Carolina to Florida, according to one study — that's faster than researchers expected.
Residents of coastal communities most often feel the effects of sea level rise during tidal flooding.
Tidal flooding, also known as "sunny day flooding" is the temporary inundation of low-lying areas, such as roads, during high-tide events — especially during "king tides," the highest tides of the year.
King tides aren't caused by sea level rise in and of themselves, but because they are the annual peak tides, they demonstrate how sea level has already risen over the past 100 years.
Sea levels aren't rising equally "like water in a bathtub," according to a report from Yale Environment 360. "The oceans are more akin to a rubber kiddie pool where the water sloshes around unevenly, often considerably higher on one side than another."
More flooding, higher costs
Climate scientists view sea level rise as one of the most obvious signals of a warming planet. Sea water expands as it warms, and melting land-based ice sheets adds to rising water levels.
There are neighborhoods that now flood on sunny days, but didn’t years ago even during especially high tides, according to the National Oceanic and Atmospheric Administration.
And as sea levels continue to rise, the frequency, depth and extent of coastal flooding will continue to worsen, according to NOAA.
In 2016, Charleston saw 50 days of tidal flooding.
Fifty years ago? Just four days.
Flooding projections are set at about 25 percent above average for 2017-18 for areas including Wilmington, according to a recent NOAA report.
Wilmington had 84 days of high-tide flooding in 2016, according to NOAA.
"It is important for planning purposes that U.S. coastal cities become better informed about the extent that high-tide flooding is increasing and will likely increase in the coming decades," according to the February 2018 NOAA report.
Sea levels rise and waters inundate storm drains and wash over flood barricades — flooding buildings and streets.
While flooding impacts might be limited or not obvious in those area right now, stormwater systems are reported to be degraded, "increasing the risk of compound flooding during heavy rains," according to NOAA.
And coastal cities should be particularly concerned that the cost of dealing with an increase of many smaller floods will be greater than major, but much rarer, flood events, NOAA said.
NC towns underwater?
A 2017 report "When Rising Seas Hit Home: Hard Choices Ahead for Hundreds of U.S. Coastal Communities" analyzed three projected scenarios of when towns and cities along U.S. coasts can expect to see the ocean rise enough to disrupt daily life.
That report found that as many as 20 North Carolina communities could be submerged by sea water in the next 15 years.
The report was created by the Union of Concerned Scientists, a U.S. nonprofit science advocacy group founded in 1969 by faculty and students of the Massachusetts Institute of Technology.
The Union of Concerned Scientists report predicts that by 2035, 13 communities clustered mostly on the mainland side of Pamlico Sound will be “chronically inundated.” The study defines that as the point at which 10 percent of a community’s usable land floods at least 26 times a year.
By 2060, that number rises to 25 communities. By 2100, it says, people 49 communities may be forced to adapt to rising water or move out.
Familiar vacation spots on North Carolina’s Outer Banks would suffer, the report said. Nags Head would have 11 percent of its land area, and Hatteras 14 percent, chronically inundated by 2045 under the highest sea level rise scenario. By 2060, it predicts, flooded areas would grow to 19 percent of the land at Nags Head and 28 percent at Hatteras.
Projections of global sea level rise range widely, from as little as 2 feet to more than 6 feet by 2100.
The Intergovernmental Panel on Climate Change estimated in a 2013 report that sea level will rise between 10.2 inches and nearly 39 inches by 2100, depending in part on future greenhouse gas emission scenarios and the effect of greenhouse gas concentrations on global temperatures and thermal expansion.
Sea-level rise scenarios have prompted opposition from some economic development interests on North Carolina’s coast that say long-range forecasts could be wrong.
When a state science panel reported in 2010 that seas on the coastline could rise by as much as 39 inches over the next century, legislators passed a law forbidding communities from using the report to make new rules.
A new report in 2015 looked only 30 years to the future and forecast a rise of 2 to 10 inches, depending on location.
Satellites and tide gauges have been used to report sea level at regular intervals in North Carolina.
That data shows that the sea level has been gradually rising consistently along the North Carolina coast for the past 30 years or more since those gauges were installed, according to the N.C. Department of Environmental Quality.
Tide gauge measurements show that relative sea-level rise is higher in the northern coastal plain (north of Cape Lookout) than in the southern coastal plain, according to NCDEQ. This is at least partly because the northern coastal plain has a higher rate of caving in or sinking than the southern plain.
The NCDEQ said possible impacts of sea-level rise in the state include:
▪ Accelerated coastal erosion.
▪ Higher storm surge flooding and property damage.
▪ Contamination of drinking water with seawater.
▪ Increased likelihood of flooding during heavy rain.
▪ More frequent flooding and drainage issues.
▪ Saltwater intrusion and salinity changes.
▪ Changes in the availability and distribution of fish.
Possible causes of East Coast flooding
Scientists have isolated several factors that appear to make the U.S. southeastern coast a hot spot of sea level rise.
One is the role of the Gulf Stream, a warm and fast Atlantic Ocean current that runs from the Gulf of Mexico to the tip of Florida, and then follows the East Coast. The Gulf Stream influences the East Coast's climate.
An example of the Gulf Stream's affect on sea level rise can be seen in 2016's Hurricane Matthew, the first Category 5 Atlantic hurricane since 2007's Felix. Matthew caused massive flooding, power outages and millions in damage throughout North Carolina because of its relentless rain and high sea levels that blocked drainage in North Carolina and in Virginia.
Matthew slowed in the Gulf Stream, stalling out over parts of the Southeast — worsening its effects.
Scientists credit the rapidly rising sea levels from Cape Hatteras in North Carolina to Miami from 2011 to 2015 (as much as 5 inches in some areas) to El Niño and other weather phenomena, including wind patterns that lead to higher water on the Eastern seaboard.