Why "Nuisance" Flooding Is the New Normal

Our warming planet's higher sea levels mean a rarity is now common.

As of Thursday, New Orleans has flooded ahead of a possible hurricane, while Pennsylvania, New Jersey, and Washington, D.C. all brace for flash flooding. These floods are linked to storm surges exacerbated by high tides — but these floods are happening in areas that, on other days, experts now say will flood with or without a storm.

According to a new report from the National Oceanic and Atmospheric Administration (NOAA), frequent flooding is the new normal for many coastal cities. This report specifically deals with high-tide flooding, a phenomenon that is increasingly common and dangerous. In the 1950s it would take a large storm like a hurricane to cause high tide flooding. Now, flooding can merely be caused by a high tide — which happens twice a day.

The NOAA report shows that in 2018 the national annual frequency of high tide flooding reached five days. This number, the national average of all the places they examined, tied the historical record that was set in 2015. Flood days broke records in the Northeast US and in the Eastern Gulf of Mexico, due to a combination of sea-level rise, hurricane seasons, and an active nor’easter.

Furthermore, more than 42 coastal locations across the United States are experiencing annual rates of high-tide flooding that are rapidly increasing, while 12 locations broke records in 2018. These locations include Washington, D.C., Wilmington, North Carolina, and Apalachicola, Florida.

coastal flooding
Coastal flooding the in Outer Banks, a group of islands off the coast of North Carolina. 

The Cause of High-Tide Flooding and Its Effects

High-tide flooding is increasing due to climate change-driven sea level rise and land sinking, combined with the loss of natural coastal barriers. How much a city floods is in part related to how much the city is prepared for the water — if the local elevation and the high tide line are close to the same in elevation, flooding will be more frequent.

As sea levels rise, more and more communities on the US coastline are experiencing water levels they previously did not need to prepare for. According to NOAA, any acceleration in sea level rise that is predicted this century will further increase the intensity of high-tide flooding impacts and reduce the time between flood events.

“Flooding that decades ago usually happened only during a powerful or localized storm can now happen when a steady breeze or a change in coastal current overlaps with a high tide,” the report states.

NOAA also notes that high-tide flood events, made worse by rising sea levels, are contributing to “over-wash and beach erosion, overwhelming storm/waste/freshwater systems, disrupting harbor operations, closing roadways, and degrading subsurface infrastructure and property values.”

For example, in 2018, high-tide flood events salted the farmlands of coastal Delaware and Maryland, degraded septic system functionality in South Florida, and flooded the roadways of the East Coast.

This video shows projected high flood days for 2018, 2019, 2030, and 2050.

Flooding in the Future

Data suggests that the problems the coasts are seeing will soon become chronic, rather than sporadic. NOAA predicts that from May 2019 to April 2020, national high-tide flooding will occur about twice as often as it did in 2000. Sea level rise will drive this increase, as well as the annual El Niño conditions that are predicted to persist through 2019.

That doubling represents what is expected to happen to the United States as a whole. Importantly, some specific regions are expected to see an even larger jump from what was seen in 2000. The report states that the Northeast Atlantic could see a 140 percent increase, the Southeast could see a 190 percent increase, and the Western Gulf of Mexico could see a 130 percent increase.

Some of these 2019 increases are already visible. For example, Boston saw 19 days of flooding between May 2018 and April 2019, a more than 200 percent increase from what was seen in 2000.

When the NOAA scientists analyzed models that went deeper into the future, long-term projections showed that by 2030 there’s expected to be a national frequency of 7 to 15 days of high-tide flooding. By 2040, that number is expected to jump from 25 to 75 days.

In 2018, the national annual frequency was five days — and still caused damage. High-tide flooding was called “nuisance flooding” in the past. Now, that occasional nuisance is more of a destructive tradition.