Sea Level Calculator

Yes there is a glossary PDF avaliable by clicking here.

This tool calculates information based on user inputs. It provides counts of days that water levels reach a user-defined threshold or the amount of sea level change that may occur in the future. It also adjusts values based on the reference datum or units (metric or standard) selected by a user. The tool graphs (bar, line, pie charts) variables as a time series with linear or nonlinear trends. It also computes how some water level metrics may change in the future with different sea level scenarios.

The majority of the data for the Calculator are collected from tide gauges operated and maintained by NOAA’s Center for Operational Oceanographic Products and Services (CO-OPS). The mapping layers are provided by NOAA’s Office for Coastal Management’s Sea Level Rise Viewer. NASA provides the data for the regional trends and extrapolations. The five sea level rise scenarios and the Regional Frequency Analysis extremes are from Global and Regional Sea Level Rise Scenarios for the United States: Updated Mean Projections and Extreme Water Level Probabilities Along U.S. Coastlines (2022 Sea Level Rise Technical Report), a synthesis of the latest available science on sea level rise developed by an interagency team of experts.

Yes. The sea level rise scenarios from the 2022 Sea Level Rise Technical Report are presented in a number of the Calculator’s Quick View sections. These scenarios represent possible future sea level changes in response to increasing greenhouse gas emissions and ocean and atmospheric warming. These science-based scenarios provide a range of plausible sea level changes, allowing people to consider future impacts and responses and ask “what if?” questions about the future to support planning and decision-making. Sea level rise scenarios are used to communicate how much sea level rise could occur, under what circumstances, and by when. They also show how sea level rise might occur globally and locally, as well as what processes will contribute to the rise.

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Sea level trends and extreme water levels are updated annually. Counts of coastal high tide flood days are reviewed monthly and will be updated on the Calculator once processing is completed. Regional trajectories and observation-based extrapolations are processed annually by NASA and will be available in the Calculator soon after the processing is completed. Sea level rise scenarios will be updated in alignment with reports from the U.S Interagency Task Force on Sea Level Change.

Future versions of the Calculator will include new, authoritative data when they become available.

Version 1 of the Calculator provides regional sea level projections at a one degree (~60 mile) grid resolution from the 2022 Sea Level Rise Technical Report. This enables users to determine regional sea level projections seamlessly along the U.S. Coast versus only at existing NOAA tide gauges, which can have extensive gaps (well beyond 60 miles), particularly along remote or rural coastlines. All other datasets, such as statistical analysis on the frequency, trend, and likelihood of coastal flooding are provided only at NOAA’s tide gauge locations. NOAA is working toward a capability to provide sea level and coastal flood information at higher spatial resolutions, which are anticipated to be included in a future release.

Version 1 will include gauges from Alaska, but no mapping data exists yet. NOAA is working on mapping individual coastal communities in Alaska for sea level rise and coastal flooding impacts.

The Calculator is based on tide gauge water level observation data. While some tide gauges do capture aspects of river discharge and wave effects, the observations do not include these effects for the most part or those from local rainfall or changes in groundwater, which can lead to coastal flooding.

The Calculator does not include the Great Lakes since sea level rise is not impacting this region, but efforts are underway to improve our understanding of how Great Lake water levels have and will continue to vary with climate change. Additional resources to explore Great Lakes Water levels include the Lake Level Viewer, and the Great Lakes Water Level Dashboard.

Data from the site’s various Quick Views can address specific questions about past and future water levels for your location. When planning for future sea levels, an Application Guide developed in conjunction with the 2022 Sea Level Rise Technical Report can help users apply and integrate sea level rise information into local planning and adaptation decisions. The guide, penned by professionals with expertise on applying sea level rise to local level planning, helps readers wade through considerations and arrive at what is best for their community. Data from the Calculator can be downloaded directly or accessed via map services and APIs for incorporation into local applications.

Extreme water levels are included in the sea level calculator in two ways for a station, through listing of the top 10 water level events and exceedance probability statistics to determine the likelihood of water levels exceeding certain heights. Two data sources of the statistical analyses are available in this calculator— the CO-OPS Extreme Water Level product and the 2022 U.S. interagency Sea Level Rise Technical Report.

The CO-OPS Extreme Water Level product data source returns water levels for various annual exceedance probabilities using a single station approach and the annual block maxima statistical methodology. Annual exceedance probability (AEP) is the likelihood that a flood of a certain magnitude or larger will occur within any given year. For example, a water level that is expected to be reached every two years would have an AEP of 50 percent. The single station approach analyzes the highest water levels observed at a single NOAA CO-OPS tide station with at least 30 years of data, describing conditions unique to that location.

The 2022 Sea Level Rise Technical Report data source returns water levels for various average event frequencies using a regional approach and the Peaks-Over-Threshold statistical methodology. Average event frequency (AEF) is the average number of times within one year that water level is expected to be reached or exceeded. For example, a water level that is expected to be reached every two years would have an AEF of 0.5 events per year. The regional approach combines data from multiple tide gauges with periods of records of at least 10 years that are geographically located near each other and share similar storm exposure and similar extreme statistics. Combining multiple stations extends the collective period of record (to the longest station record) and records the maximum water level reached across all stations in that region to provide a more regional perspective. The calculator includes stations with long-term and short-term periods of data where downscaling is performed from the regional information, increasing the spatial coverage of estimating extreme water levels along the coast.

NOAA and the Federal Emergency Management Agency (FEMA) calculate extreme water level probabilities differently and use this information for different purposes. FEMA’s calculations of the one percent annual chance event level (often referred to as the 100-year event) are based upon a combination of storm-tide observations, wave effects, synthetic storm simulations, and high water marks. These calculations combined are not directly measured by a local tide gauge. The calculations support the National Flood Insurance Program that administers the national flood hazard layer and the Federal Flood Management Standard (FFRMS) Floodplain.

Extreme water levels displayed in the Calculator are based solely on observation data collected at NOAA tide gauges and are used for planning, not regulatory, purposes.

Annual exceedance probabilities in this tool are not shown for return periods longer than 50 years, which equates to the two percent annual exceedance probability from the CO-OPS data source and the 0.02 events per year average event frequency from the 2022 Sea Level Rise Technical Report data source. This is to eliminate confusion between these observation-only based extreme water levels calculation and FEMA’s base flood elevations and stillwater elevations calculations, which are computed using different statistical methodology and modeling methods for the one percent annual exceedance probability levels. NOAA and its federal partners are working together to ensure consistency in estimating extreme water levels across varying methods and annual probabilities.