USA: Rising seas, flooding coasts

Source(s): Climate Central

Key concepts

  • As sea levels rise, flooding is becoming more common along U.S. coasts, where about 30% of the population lives.
  • High tide flooding can occur in the absence of heavy rainfall or storms, and the effects can be disruptive, dangerous, and costly for coastal communities. 
  • The annual frequency of high tide flooding in the U.S. has more than doubled since 2000 — and is projected to more than triple again by 2050 as sea levels continue to rise. 
  • According to NOAA outlooks for 2023, the annual risk of high tide flooding is expected to peak during late September and October in many locations along the East and Gulf Coasts. 

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

Click the downloadable graphic: National Sea Level Rise and Coastal Flooding

Coastal communities face more floods

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., where 29% of the population lives in coastal counties. 

As global sea levels rise, water levels along the coast rise too. As daily tides cycle over higher baseline water levels, high tide lines migrate farther inland or upslope — regularly flooding coastal areas that previously would have flooded only during storms or extreme rainfall events. 

High tide flooding happens when water levels exceed 1-2 feet above the daily average high tide (the threshold for minor high tide flooding).

CM: Local Coastal Flooding 2023 (EN)

Click the downloadable graphic: Local Coastal Flooding

High tide flooding: disruptive, dangerous, and costly 

Such flooding can clog storm water drains, flood streets, inundate coastal infrastructure and ecosystems, and affect freshwater supplies. 

These impacts worsen during so-called king tides, the highest astronomical tides of the year. Flood risks compound if extreme high tides also overlap with heavy rains or storms. 

Earlier this year, NOAA released a new interactive Monthly High Tide Flooding Outlook that shows how likely high tide flooding is on each day of the year at 98 coastal U.S. locations. 

According to NOAA outlooks for 2023, the annual risk of high tide flooding is expected to peak during late September and October in many locations along the East and Gulf Coasts. 

CM: Local Sea Level Trends 2023 (EN)

Click the downloadable graphic: Local Sea Level Trends

Warming planet, rising seas, flooding coasts

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. 

Rising sea levels have contributed to the increased frequency of coastal flooding in the U.S. — especially in the last two decades.

More high tide flood days 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

The Northeast, Southeast, and Gulf Coasts have experienced the largest historical increase in high tide flooding. 

Last year, eight U.S. locations saw record or record-breaking numbers of high tide flood days, including in Florida, Puerto Rico, Virginia, Georgia, and Washington state. 

A strengthening El Niño could further boost coastal flooding during 2023-2024 along both the East and West Coasts due to regional effects on storms and sea level. 

Coastal flooding: not only a coastal issue

The latest science is clear: we can expect more coastal flooding far into the future, due to rising emissions causing rising sea levels

In the absence of measures to both rapidly curb emissions and reduce risk, coastal flood impacts are likely to become increasingly damaging and destructive. 

People, ecosystems, and infrastructure along the coast will be directly affected by flooded homes, streets, and businesses, erosion, stormwater overflows, and reduced water quality. 

But such impacts along U.S. coasts can have far-reaching effects. 

U.S. coasts are essential for trade and supply chains we all depend on. They’re home to large and growing populations. Recreation, tourism, and fisheries are all thriving coastal industries. And ecosystems such as wetlands provide coastal protection, wildlife habitat, and carbon storage. 

Thus, the entire country is directly or indirectly affected by the inundation of our coasts as sea levels continue to rise.

Reversing recent trends ultimately requires rapid and sustained emissions cuts. But even under low-emissions scenarios, sea levels will continue to rise. 

Ways that coastal communities can reduce risk and enhance resilience to future flooding include raising roads, stabilizing shorelines, relocating low-lying buildings, and restoring coastal ecosystems.

Local story angles

What’s the flooding outlook in your local area?

NOAA’s Annual and Monthly High Tide Flooding Outlooks show when and where high tide flooding is most likely in 98 coastal U.S. stations, to guide seasonal planning and preparedness. The Annual Outlook also provides local high tide flooding projections for 2050. Both outlooks are integrated into NOAA’s Coastal Inundation Dashboard which provides 48-hour forecasts and local images of recent floods. The National Weather Service provides real time coastal flood watches, warnings, and advisories

What’s at risk in your nearest coastal area?

Use NOAA’s Coastal County Snapshots to explore, visualize, and download data about flood hazards, sea level rise, and the marine and coastal economy in 850+ coastal counties across 37 coastal states and territories. Go deeper with NOAA’s Coastal Flood Exposure Mapper to locate people, infrastructure, and ecosystems exposed to flood hazards along U.S. coasts. Use Climate Central’s Risk Finder and Picturing Our Future tools to explore local risk and visualize how 190 landmark sites would be affected under different warming scenarios. 

How are sea levels and coastal floods changing in your area? 

The Interagency Sea Level Rise Scenario Tool from NASA and NOAA provides sea level rise projections for each decade through 2150 for: the entire U.S., major coastal regions, and individual tide gauge stations along the coast. Use The Climate Explorer, part of the U.S. Climate Resilience Toolkit, to chart past and future high tide flooding in your city. Climate Central’s Coastal Risk Screening Tool can be used to map areas at risk from sea level rise and coastal flooding under a range of warming scenarios. Use 

Contact experts

Kate Silverstein (she/her/hers)
NOAA National Ocean Service
Can connect to experts on: Sea level rise and coastal flooding
Contact: katherine.silverstein@noaa.gov, oceanservicepress@noaa.gov

For questions about Climate Central’s suite of sea level rise tools, please contact: Kelly Van Baalen, project manager, at kvanbaalen@climatecentral.org.

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