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Coastal Salinity Index (CSI)

Associated Agencies

U.S. Geological Survey

    The Coastal Salinity Index (CSI) is a long-term monitoring tool that characterizes relative changes in coastal salinity regimes for salinity gages with long periods of record. The CSI was developed to characterize coastal drought, monitor changing salinity conditions, and improve our understanding of the effects of changing salinities on fresh and saltwater ecosystems, fish habitat, and freshwater availability, providing economic, human health, and environmental benefits.

    • The CSI uses an approach similar to the Standardized Precipitation Index (SPI) to show the probability of recording a given amount of salinity. A value of zero indicates historical mean salinity, and positive and negative values represent increasingly fresh and saline conditions, respectively. 
    • The CSI uses the same classification scheme as the U.S. Drought Monitor for high saline (or drought) conditions and the inverse for wet conditions.
    • The CSI can be computed for multiple time intervals from 1 to 24 months to characterize short- and long-term conditions.
    • The CSI does not depict hourly to daily salinity fluctuations, but the response to monthly (and longer) precipitation and streamflow conditions.

    The Coastal Salinity Index project has been supported by the National Integrated Drought Information System (NIDIS), the National Oceanic and Atmospheric Administration (NOAA), the Carolinas Integrated Sciences and Assessments program (a NOAA RISA), and the U.S. Geological Survey.

    Interactive Map: Coastal Salinity Index (CSI)

    The U.S. Geological Survey offers coastal salinity data in text formats (e.g., CSV and JSON). Data were ingested and joined to a station point layer to provide a visualization of the data.

    Access Data Files

    Coastal Salinity Classification
    Value Map Hex Color
    CD4 - Exceptional Salinity Conditions #730000
    CD3 - Extreme Salinity Conditions #e60000
    CD2 - Severe Salinity Conditions #ffaa00
    CD1 - Moderate Salinity Conditions #fcd27f
    CD0 - Abnormal Salinity Conditions #ffff00
    Normal Salinity Conditions #0000ffff
    CW0 - Abnormal Freshwater Conditions #e4e1ea
    CW1 - Moderate Freshwater Conditions #b6d0e5
    CW2 - Severe Freshwater Conditions #91abd0
    CW3 - Extreme Freshwater Conditions #33648d
    CW4 - Exceptional Freshwater Conditions #23425f

    How To

    Click on any station icon on the map to access the following information:

    • The station identification number, station name, and a link to the National Water Information System station current conditions page data.
    • The current CSI 12-month interval value.
    • The CSI stacked graph that allows the user to evaluate short- (1-month) to long-term (24-month) conditions in one graph. Learn how to read the stacked graph.
    • A link to all the CSI graphs for that particular gauge.

    You can also download CSV files with data for specific stations or all stations.


    Coastal Salinity Index Tool: View the CSI on the U.S. Geological Survey website


    About the CSI: Learn about the motivations and methodology behind this tool