Sea Level Trends and Extremes Beta

Map:

English Metric

The map above illustrates relative sea level trends, with arrows representing the direction and magnitude of change. Click on an arrow to access additional information about that station.

Station View

Select Station to see Trends Plots

Timeframe:

The plot shows changes in mean sea level at the station from the National Tidal Datum Epoch (NTDE)1983-2001 to present. The horizontal black lines highlight the 1983–2001 epoch baseline and the most recent five-year average, with the net change between them indicated in red. Present day mean sea level is represented as the average of the most recent five years and marked at its central midpoint.

Relative sea level change is influenced by both ocean-related factors and land movement, resulting in positive or negative amounts of change. Positive relative sea level change means the sea level is rising relative to the land. Negative relative sea level change means the land is rising more quickly than the ocean.
All calculated amounts of sea level change are available via CO-OPS API. Users can toggle between two views of change, either from the midpoint of the NTDE (default) or for the full period of record. While most stations have both options for the amount of relative sea level change, there are some exceptions:

Three stations: Morgans Point, TX (8770613), Eagle Point, TX (8771013), and Nikiski, AK (9455760) lack the National Tidal Datum Epoch (NTDE) option because their data series began in the 1990s and their control stations are on a Modified Tidal Datum Epoch (MTDE). Forcing an NTDE offset would only introduce additional error.
Some stations do not have the POR option due to less than 70% completeness of monthly means in the first five years of the data record or due to datum shifts in the verified monthly data.

The total amount of change since the midpoint of the NTDE to present is the difference between the zero mean sea level (MSL) value of the NTDE and the five-year average of the latest monthly MSL values. To maintain consistency, the five-year average must have a monthly data completeness of 70%. The zero MSL value for each station is defined as the NTDE MSL datum.

For stations using a Modified Tidal Datum Epoch (MTDE), an offset is applied to align the data with the NTDE. This offset is determined by calculating the average monthly MSL from 1983–2001 and subtracting it from the data, thereby centering the values at the NTDE midpoint. These MTDE stations and their corresponding MSL offsets are available in CO-OPS API.

The total amount of change for the full POR is the difference between the average of the first five years of monthly MSL values (with a monthly data record that is at least 70% complete), and a five-year average of the most recent monthly MSL values (with a monthly data record that is at least 70% complete).

The data plot also features additional station-specific details where applicable. For stations with major earthquakes in their records, the plot includes a solid vertical line to denote the date of those events. Periods of questionable data or possible datum shifts are denoted by long, dashed vertical lines to highlight these in the station’s period of record.

Landsat Imagery

To complement observed sea levels at tide gauge stations, Google’s Earth Timelapse incorporates satellite observations from the Landsat program. Managed jointly by NASA and the USGS, these satellites gather thermal and multispectral data, capturing images of the entire planet at a 30-meter resolution approximately every two weeks. This continuous record of Earth’s surface spans from 1972 to the present day.

Because coastal zones are inherently vulnerable to the risks associated with changing sea levels, this historical imagery is valuable for tracking environmental shifts. It illustrates ongoing modifications to coastlines driven by several factors, including:

The expansion of urban areas
Deforestation
The meandering of rivers
Agricultural development and expansion
Erosion along shorelines
The dynamic movement of barrier islands

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The plot shows monthly mean sea levels with the seasonal cycle removed and the average linear rate of change at the station. The rate of change was computed from the central midpoint of NTDE 1983-2001 to the end of the most recent year with data . The shaded region represents the 90% confidence interval.

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The plot shows monthly mean sea level observations at the station over its period of record. Values are relative to the station’s accepted NTDE 1983-2001 mean sea level (MSL) datum, i.e., a value of 1.0 feet means monthly mean sea level for that month was 1.0 feet above that station’s MSL datum.

Select Station to see Extremes Plots

The above plot shows the monthly maximum water level (in blue) as well water levels that represent four different annual probability frequencies (1%, 10%, 50%, and 99%). For example, the 10% Annual Exceedance Probability (AEP) level represents the water level that has a 10% chance of occurring for that year. The AEP lines change over time in accordance with the average linear change of mean sea level.

The above plot shows the monthly minimum water level (in blue) as well water levels that represent four different annual probability frequencies (1%, 10%, 50%, and 99%). For example, the 10% Annual Exceedance Probability (AEP) level represents the water level that has a 10% chance of occurring for that year. The AEP lines change over time in accordance with the average linear change of mean sea level.

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The plot shows water levels representing four different annual probability frequencies: 1% (in red), 10% (in orange), 50% (in blue), and 99% (in purple), for both the 1983-2001 period (averaged) and the most recent year. For example, the 10% annual exceedance probability (AEP) level represents the water level that has a 10% chance of occurring for that time period. In most locations, data are shown relative to the station’s mean sea level (MSL) datum with other tidal datums shown for reference. Where sea level rise is occurring, all values in the most recent year will be larger than those averaged over 1983-2001.

The plot shows the annual exceedance probability (AEP) curve from the 99% to 1% probability levels and represents water levels that have that specific AEP chance of occurring. For example, the 10% AEP level represents the water level that has a 10% chance of occurring within a single year. Water level values are relative to the mean higher high water (MHHW) datum, and the points around the curves represent detrended annual maxima that have been observed in the past. The shaded region represents the 90% confidence interval.

The plot shows the annual exceedance probability (AEP) curve from the 99% to 1% probability and represents water levels that have that specific AEP chance of occurring. For example, the 10% AEP level represents the water level that has a 10% chance of occurring within a single year. Water level values are relative to the mean lower low water (MLLW) datum, and the points around the curves represent detrended annual minima that have been observed in the past. The shaded region represents the 90% confidence interval.

AEP ARI

The plot shows water levels that occur with the Average Recurrence Interval (ARI) between events. For example, the water level at the 10-year ARI has occurred about every 10 years, on average. Likewise, the 0.5-year ARI water level has occurred about every 6 months, on average. Water level values are relative to the station’s mean higher high water (MHHW) datum. Data in this plot were computed by the US Interagency Task Force on Sea Level and differ from the extreme water level plots from NOAA CO-OPS. The plot’s data incorporate observations from surrounding tide gauges, a process known as regional frequency analysis (RFA). RFA extends the period of record and spatial coverage at the expense of local specificity. The shaded region represents the 90% confidence interval.

Regional Frequency Analysis (RFA)

RFA is a statistical method used to estimate the frequency distribution of extreme events at locations where limited or no data is available. It involves pooling data from multiple sites within a region to develop regional frequency curves or equations that can be used to estimate the frequency of extreme events at sites without tide gauges.
These average recurrence intervals (ARI) and corresponding water levels are based on a RFA of National Ocean Service tide gauges within a 400-km radius of the center of each individual 1-degree grid and fit with a generalized Pareto distribution (GPD) of high water levels that exceeded a certain threshold. Each RFA plot shows data downscaled from the grid to the specific station of interest.

Key Differences between Average Recurrence Interval (ARI) and Annual Exceedance Probability (AEP)

ARI and AEP are two statistical methods used to describe the severity and likelihood of extreme events like floods. ARI expresses the average time span between events of a specific magnitude, while AEP states the probability that an event of a given size will occur or be exceeded in any single year.
While both quantify the same event, they present the data differently (notably, AEP is the inverse of ARI).
- ARI, also known as the "return period", estimates the average length of time (in years) between events of the same or greater magnitude. For example, a 100-year ARI storm will occur, on average, once every 100 years.
- AEP is the probability of a specific-sized event occurring in any given year, typically expressed as a percentage. For example, a 100-year ARI flood translates to a 1% AEP, meaning there is a 1-in-100 (or 1%) chance of that flood level being equaled or exceeded in any single year. Subject matter experts are increasingly recommending referring to AEP as the “X% chance per year” as the most accurate way to convey the ongoing annual risk of a flood in a given location.

Select Station to see Variability Plots

The plot shows the detrended and deseasonalized monthly mean sea level (MSL) at the station from the National Tidal Datum Epoch (NTDE) 1983-2001 to present. The gray line shows mean sea level observed each month at the tide gauge, whereas the blue line shows the same data smoothed using a 5-month moving mean to highlight the seasonal to annual variability.

The plot shows the average linear trend rate of change of mean sea level for each year centered on a 30-year window. The shaded region represents the 90% confidence interval for the trend rate during that 30 year period.

The plot shows the average seasonal cycle of monthly mean sea level at the station over the period from the mid-year of the National Tidal Datum Epoch 1983-2001 to present. The shaded region represents the 90% confidence interval for the mean value of each month.

The plot shows high water levels that represent four different annual probability frequencies: 1% (in red), 10% (in orange), 50% (in green), and 99% (in purple), for each month of the year. For example, the 10% annual exceedance probability (AEP) level represents the water level that has a 10% chance of occurring for that year. These extreme levels were computed over each station’s period of record and are relative to each station’s National Tidal Datum Epoch 1983-2001 mean higher high water (MHHW) datum.

The plot shows low water levels that represent four different annual probability frequencies: 1% (in red), 10% (in orange), 50% (in green), and 99% (in purple), for each month of the year. For example, the 10% annual exceedance probability (AEP) level represents the water level that has a 10% chance of occurring for that year. These extreme levels were computed over each station’s period of record and are relative to each station’s National Tidal Datum Epoch 1983-2001 mean lower lower water (MLLW) datum.

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Select Region:

Map:

English Metric

REGION SELECTED: Map illustrating the rates of vertical land motion at National Ocean Service tide stations, represented by arrows showing the direction and magnitude of change.

Regional View

Data Snapshot

The top plot shows vertical land motion (VLM) for all stations in the region. Blue bars represent land uplift, and red bars represent land subsidence.

The bottom plot shows relative sea level change rates since the mid-year of the National Tidal Datum Epoch 1983-2001 at all stations in the region, expressed as a combination of local (absolute) sea level and local vertical land motion. Blue bars indicate increasing sea levels, and red bars indicate the land is rising more quickly than the sea at that station.

Note: only stations with both vertical land motion (VLM) and sea level trend (SLT)and SLT data are shown in the regional view.

NO REGION SELECTED: Map illustrating the locations of National Ocean Service tide stations. Click on a pin or select a region from the dropdown to see regional information

Sea Level Trends and Extremes Beta

Station View

Landsat Imagery

Github Notebooks

Regional View

Northeast: Eastport, Maine to Kings Point, New York

Mid-Atlantic: New York City, New York to Southern Virginia

Southeast: Duck, North Carolina to Key West, Florida

Pacific Southwest: San Diego, CA to Arena Cove, CA

Pacific Northwest: Eureka, CA to Friday Harbor, Washington

Gulf Coast: Naples, Florida to Port Isabel, Texas

Alaska: Ketchikan, AK to Prudhoe Bay, AK

Pacific Islands: Hawaii, American Samoa, Marshall Islands, and Guam

Pacific Islands: Hawaii, American Samoa, Marshall Islands, and Guam

Caribbean: Virgin Islands and Puerto Rico

Github Notebooks