Last updated November 28, 2017

Increased Coastal Flooding

Global sea level rise has elevated tidal systems, causing tides to reach higher and extend significantly further inland along low-lying coastlines.

 

Sea level rise and storm surge

Due to the melting of land ice and the expansion of sea water as it warms, global sea level has risen 8 inches since 1880.[1] 

While sea level rise may be modest relative to the total height of storm surge, disaster usually strikes when a threshold is crossed. Human infrastructure and natural systems have developed to cope with a range of historical extremes. New, more intense extremes can overwhelm and collapse existing human systems and structures.

When sea level rides on top of storm surge, it can be responsible for a disproportionate amount of damage. A small vertical increase in sea level can translate into a large increase in horizontal reach by storm surge depending upon local topography.

Sea level rise, combined with coastal storms, has increased the risk of erosion, storm-surge damage, and flooding for coastal communities, especially along the Gulf of Mexico, the Atlantic seaboard, and Alaska.[1]


Sea level rise and high tides

High tides are a problem even on storm free days—a phenomenon known as “nuisance flooding.”[2][3] Sea level rise boosts high tides so that they reach higher and extend further inland than in the past, increasing the risk of coastal flooding during high tide events.

In Florida alone, more than 30,000 people live on land for each vertical inch above the high tide line, averaged across the first six feet.[4] About 5 million people in the United States live less than 4 feet above high tide. Nearly half of them live in Florida.[5]


US trends

Since 1950, about two-thirds of the US coastal floods in 27 different locations were linked to human-made warming.[6]

NOAA water level gauges document an increasing frequency of tidal flooding around much of the US, which is driven primarily by local relative sea level rise.[7] 

Nuisance flooding has already increased 300 to 925 percent due to sea level rise to date.[8]