Coastal flood exposure is already measurable in recurring high-tide flooding, the people and property located near current sea levels, and the thresholds at which roads and communities experience disruption. The scale is also changing: NOAA projects a national median of 7–12 high-tide flood days for May 2026–April 2027, while the Fifth National Climate Assessment projects about 11 inches of contiguous U.S. coastal sea-level rise between 2020 and 2050.
Contents
- Observed U.S. high-tide flooding
- Regional and local exposure
- People, property, and coastal economies
- Infrastructure thresholds and flood indicators
- Sea-level rise and future exposure
- Storm-driven and compound flooding
Observed U.S. high-tide flooding
High-tide flood counts describe threshold exceedances recorded at water-level stations. They are not interchangeable with storm-surge inundation or permanent sea-level inundation. NOAA reports these observations and outlooks by meteorological year, running from May through April.
For the 2025–2026 meteorological year, 42% of NOAA stations observed flooding within the predicted range. Another 36.5% recorded fewer flood days than predicted, while 21.5% recorded more. The same year, Apra Harbor, Guam, recorded a station-record 77 high-tide flood days.
The national record in this set also shows variation between years. The national annual high-tide flood frequency averaged 4 days in 2022, compared with an average of 5 days in 2018. The 2023–2024 meteorological year produced a national average of 7–8 high-tide flood days. NOAA predicted 4–8 national days for May 2024–April 2025, followed by the higher 7–12-day national median outlook for May 2026–April 2027.
These figures come from NOAA’s Annual High Tide Flooding Outlook and its High Tide Flooding indicator. A forecast is an estimate for a defined future period; it should be read separately from the observed station counts.
Regional and local exposure
National medians can conceal large differences between coastlines. During May 2025–April 2026, the Northeast had a regional median of 2 high-tide flood days. Boston recorded 6 days, the Northeast’s highest station count in the reported comparison.
The Mid-Atlantic had a regional median of 9 days. Two Virginia stations were higher: Windmill Point recorded 18 days and Sewells Point recorded 17. The Southeast had a regional median of nearly 7 days, while Duck, North Carolina, recorded 19 days.
The Eastern Gulf had a regional median of 0 days in the same meteorological year. Bay Waveland, Mississippi, nevertheless recorded 6 days, the highest station count reported for that region.
| Region or station | High-tide flood days | Measurement period |
|---|---|---|
| Northeast regional median | 2 | May 2025–April 2026 |
| Boston | 6 | May 2025–April 2026 |
| Mid-Atlantic regional median | 9 | May 2025–April 2026 |
| Windmill Point, Virginia | 18 | May 2025–April 2026 |
| Sewells Point, Virginia | 17 | May 2025–April 2026 |
| Southeast regional median | Nearly 7 | May 2025–April 2026 |
| Duck, North Carolina | 19 | May 2025–April 2026 |
| Eastern Gulf regional median | 0 | May 2025–April 2026 |
| Bay Waveland, Mississippi | 6 | May 2025–April 2026 |
The station values and regional medians are reported by NOAA in the Annual High Tide Flooding Outlook. They show why coastal conservation and resilience planning need local water-level records as well as national summaries.
People, property, and coastal economies
Exposure is not only a count of flood days. It also depends on how many people, homes, businesses, and public assets occupy low-lying coastal areas. The Fifth National Climate Assessment reports that about 2.2 million people lived below high-tide elevations plus 3.3 feet of sea-level rise in 2020. That population increased by about 14%–18% from 1990 to 2020 under the reported definition.
An EPA coastal-flooding assessment cited more than 8.6 million Americans living in areas susceptible to coastal flooding and more than $1 trillion in property and structures within a few feet of current sea level. Those figures refer to the assessment cited by EPA for 2014, rather than a current nationwide inventory.
NOAA’s coastal-community estimate provides another measure of concentration. The 2010 Census count found that 39% of the U.S. population lived in counties subject to significant coastal flooding. NOAA also reports an estimate of about 164 million people, or more than half of the U.S. population, living or working in coastal counties, and estimates that coastal counties generated 58% of U.S. gross domestic product. The page for these estimates was accessed in 2026, but the figures retain the source’s stated definitions and periods.
The economic and human consequences of coastal hazards extend beyond routine high tides. The Fifth National Climate Assessment reports that 38 tropical cyclones caused more than $1 trillion in U.S. losses, in 2022 dollars, and 6,200 deaths between 2000 and 2021. These totals cover tropical cyclones and should not be treated as high-tide-flood totals.
Sources for these measures include the Fifth National Climate Assessment, Chapter 9: Coastal Effects, EPA’s Climate Change Indicators: Coastal Flooding, and NOAA’s Expanded Flood Information Tool.
Infrastructure thresholds and flood indicators
Flood categories are tied to local water-level reference points and physical impacts. NOAA’s national threshold analysis places average minor-flood vulnerability at about 0.5 meters above Mean Higher High Water, average moderate-flood vulnerability at about 0.8 meters, and average major-flood vulnerability at about 1.2 meters. The analysis was published in 2018, so these are threshold-analysis values, not a forecast of a particular community’s flood date.
Local thresholds differ. EPA gives Wilmington, North Carolina, as an example where the minor-flood level is approximately 10 inches above the average high-water mark. In Galveston, Texas, the cited minor-flood level is approximately 31 inches above that location’s average high-water mark. The difference illustrates why exposure comparisons should identify the gauge, datum, and local definition.
EPA’s coastal-flooding indicator uses 27 tide gauges with complete data from 1950 to the present, according to the page updated in 2016. In that indicator, high-tide flood days increased by more than 400% in the Southeast Atlantic and by 1,100% in the Gulf Coast relative to 2000. NOAA’s 2018 analysis also found that annual high-tide flood frequency was increasing or accelerating at two-thirds of roughly 100 U.S. locations examined.
A typical high-tide flood event lasts about 2 days and several high tides, according to the Fifth National Climate Assessment. Duration matters for coastal conservation and community response because repeated nuisance flooding can affect access, drainage, habitats, and public infrastructure even when individual events do not resemble a major storm.
Sea-level rise and future exposure
The Fifth National Climate Assessment projects about 11 inches of contiguous U.S. coastal sea-level rise from 2020 to 2050. Its likely range is 9–13 inches relative to 2020. These are projections, not observations already completed.
| Projection or observation | Amount | Period or reference |
|---|---|---|
| Contiguous U.S. projected coastal rise | About 11 inches | 2020–2050 |
| Likely contiguous U.S. projected range | 9–13 inches | By 2050, relative to 2020 |
| Intermediate-to-High scenario range | About 3.6–6.9 feet | By 2100, relative to 2020 |
| Intermediate-to-High scenario range | About 6.9–12.5 feet | By 2150, relative to 2020 |
| Western Gulf Coast relative rise | About 9 inches | 1990–2020 |
| Hawaiian and U.S. Caribbean island coastlines | About 4 inches | 1990–2020 |
The same assessment reports that contiguous U.S. coastlines experienced about 11 inches of sea-level rise over 1920–2020, with about 5–6 inches occurring during 1990–2020. It projects 3.6–6.9 feet by 2100 and 6.9–12.5 feet by 2150 under Intermediate-to-High sea-level scenarios, each relative to 2020.
Global observations show a change in rate across the reported periods. Global mean sea level rose about 0.05 ± 0.01 inches per year during 1901–1990, about 0.13 ± 0.02 inches per year during the 1993–2022 satellite era, and about 0.17 inches per year during 2013–2022.
Local projections can be higher or lower than national summaries. Grand Isle, Louisiana, is projected to see 22–32 inches of sea-level rise by 2050. The assessment also projects that major flood events in Jacksonville, Florida, could become about 5 times more likely by 2050 and occur about once per decade.
Storm-driven and compound flooding
Coastal flood exposure can combine tides, waves, storm surge, rainfall, and rising baseline water levels. Wave-driven water levels comprise 25%–90% of extreme coastal water levels along exposed U.S. coastlines, according to the Fifth National Climate Assessment. This range means that the storm-facing shape and exposure of a coastline matter alongside the tide gauge’s baseline.
NOAA’s nationally consistent definitions describe minor disruptive flooding at about 1.75–2 feet above average high tide, moderate damaging flooding at about 2.75–3 feet above average high tide, and major destructive flooding at about 4 feet above average high tide. These definitions use a 2020 baseline threshold definition in the cited assessment.
Observed frequency has already shifted in many places. Annual minor and moderate coastal-flood frequencies increased by a factor of 2–3 along most Atlantic and Gulf coasts between 1990 and 2020. Without adaptation, minor, moderate, and major coastal-flood frequencies are projected to increase about 5–10 times relative to 2020 in many regions by 2050.
The projected change is a frequency estimate under the stated no-adaptation condition, not a claim that every station or community will experience the same multiplier. It should be considered alongside local elevation, shoreline conditions, drainage, wave exposure, and the reference level used for each threshold. For coastal conservation, the practical signal is that recurring exposure can grow before a community reaches the levels associated with destructive storm flooding.