Extreme Weather Toolkit: Coastal Flooding

CM: National Sea Level Rise and Coastal Flooding 2023 (EN)

The frequency of coastal floods has risen sharply in recent decades. Rising sea levels due to human-caused warming will continue to increase both tidal flooding and flooding from extreme weather events in the years ahead.

The oceans absorb 90% of the extra heat caused by carbon pollution. As oceans heat up, the volume of seawater expands — causing sea levels to rise. Melting glaciers and ice sheets also contribute to rising sea levels. 

Global mean sea level rose 7.8 inches from 1901 to 2018, according to the latest IPCC reports. Sea levels have been rising faster since the late 1960s, and human activities are the primary cause

Sea level rise is accelerating along U.S. coasts. According to NOAA, sea levels along U.S. coasts are expected to rise as much over the next 30 years (10-12 inches, on average) as they did over the last 100 years. 

As sea levels rise, flooding is becoming more common along U.S. coasts, where 29% of the population lives.

In our warming climate, it no longer takes a strong storm to flood streets, homes, businesses, and ecosystems along the coast.  High tide flooding — also called nuisance flooding or sunny day flooding — is becoming more common in the U.S.

The annual frequency of U.S. high tide flooding has more than doubled since 2000. Flood frequency is projected to more than triple again by 2050 (relative to 2020) to reach a national average of 45 to 85 flood days per year.

Updated: April 2024