Nearshore waves in southern California: hindcast, and modeled historical and 21st-century projected time series

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Nearshore waves in southern California: hindcast, and modeled historical and 21st-century projected time series
Abstract: This data release presents modeled time series of nearshore waves along the southern California coast, from Point Conception to the Mexican border, hindcasted for 1980-2010 and projected using global climate model forcing for 1975-2005 and 2012-2100. Details: As part of the Coastal Storm Modeling System (CoSMoS), time series of hindcast, historical, and 21st-century nearshore wave parameters (wave height, period, and direction) were simulated for the southern California coast from Point Conception to the Mexican border. Changes in deep-water wave conditions directly regulate the energy driving coastal processes. However, a number of physical processes, for example, refraction on continental shelves and/or diffraction by islands, transform deep-water waves as they propagate to the nearshore, which complicates large-scale modeling efforts. In this work, a hindcast of nearshore waves was simulated by forcing a numerical wave model with hindcasted intermediate-water waves and reanalysis winds. A lookup table was created by relating corresponding offshore winds and waves with nearshore wave conditions. Using the lookup table, historical and 21st-century nearshore-wave time series were generated for global climate model-forced offshore winds and waves. Three-hourly wave parameters from the U.S. Army Corps of Engineers Wave Information Studies (WIS; and near-surface winds (10 m above ground) from the California Reanalysis Downscaling at 10 km (CaRD10; Kanamitsu and Kanamaru, 2007) were used to force the Simulating Waves Nearshore (SWAN) numerical model in stationary mode over a curvilinear grid extending along the coast from Point Conception to the Mexican border and from the shoreline to approximately 25 km offshore to hindcast the time period 1980-2010. The offshore extent of the model domain was defined by the locations of WIS stations used for forcing. Horizontal-grid resolution varies largely depending on bathymetry and shoreline curvature, ranging from 24 to 543 m in the along- and across-shore directions. Bathymetry data are from the 2013 Coastal California TopoBathy Merge Project (National Oceanic and Atmospheric Administration, 2013). Wave spectra were computed with a JONSWAP shape, 10-degree directional resolution, and 34 frequency bands ranging logarithmically from 0.0418 to 1 Hz. Three-hourly nearshore wave parameters (significant wave height [Hs], mean wave period [Tm], peak wave period [Tp], mean wave direction [Dm], and peak wave direction [Dp]) were output from the simulations at the 10-m bathymetric contour approximately every 100 m in the alongshore direction at a total of 4,802 locations in the nearshore and at an additional 23 locations coincident with California Data Information Program (CDIP; Scripps Institute of Oceanography; wave buoys. A lookup table was generated by relating offshore wind and deep-water wave conditions at a single offshore point and nearshore wave conditions simulated by the wave hindcast. The open boundary of the SWAN simulation does not represent deep-water wave conditions, as it is located in intermediate water and shoreward of the Channel Islands. Therefore, the NOAA WW3 Climate Forecast System Reanalysis Reforecast (CFSRR; Chawla and others, 2012) wave time series at a single point (CDIP buoy 067, equivalent to National Data Buoy Center station 46219) defined the deep-water end member. The lookup table was based on binning CFSRR deep-water wave parameters (Hs, Tp, Dp) and CaRD10 wind speed (U) at CDIP 067. Significant wave height was binned from 0.5 to 10.25 m at 0.25-m intervals; peak wave period was binned from 3 to 24 s at 3-s intervals; peak wave direction was binned from 5 to 360 degrees at 5-degree intervals; and wind speed was binned from 0 to 24 m/s at 6-m/s intervals. Interval sizes for Hs and Tp were based on the average RMSE for each variable. For each combination of deep-water Hs, Tp, Dp, and U, time indices falling into each bin were identified. For each nearshore location, median Hs, Tp, Tm, Dp, and Dm corresponding to all time indices of a given set of deep-water binned conditions were computed to complete the lookup table. Because swell travel time from offshore to nearshore is on the order of 1.5 h (assuming an average depth of 100 m and Tp of 15 s over a distance of about 120 km) and the model outputs are at three-hourly intervals, we assume no time lag between deep water and nearshore conditions. Historical (1976-2005) and 21st-century (2012-2100) deep-water wave time series at CDIP 067 were derived from the WaveWatch3 wave model over global (1.25 deg x 1.25 deg) and nested eastern North Pacific regional (0.25 deg x 0.25 deg) grids forced by three-hourly near-surface wind fields from a global climate model (GCM; GFDL-ESM2M RCP 4.5). Wind (CaRD10 and GFDL-ESM2M at CDIP 067) and coincident deep-water wave time series were passed through the lookup table to generate historical and 21st-century nearshore wave conditions. Wind and wave conditions that were not present in the lookup table or that had not occurred in the hindcast were filled using quantile relationships. Outputs include: southern California three-hourly, nearshore wave parameters (Hs, Tp, Dp, Tm, Dm) for 4,802 locations approximately 100 m apart along the 10-m bathymetric contour from Point Conception to the Mexican border and for an additional 23 points collocated with CDIP wave buoys. Wave parameters are available for three periods: 1) a validated hindcast (1980-2010) period derived from reanalysis data, 2) a historical (1976-2005) projection derived from GFDL-ESM2M (GCM-historical), and 3) a 21st-century (2012-2100) projection also derived from GFDL-ESM2M. Data are available as NetCDF files packaged by region, with each file containing the time series for roughly 600 locations. The points collocated with wave buoys are within one separate file. References: Chawla, A., Spindler, D., and Tolman, H., 2012, 30 Year Wave Hindcasts using WAVEWATCH III with CFSR winds--Phase 1: National Oceanic and Atmospheric Administration, National Weather Service, Environmental Modeling Center, Marine Modeling and Analysis Branch, Technical note, MMAB Contribution n. 302, 12 p. with Appendices. Kanamitsu, M., and Kanamaru, H., 2007, 57-Year California Reanalysis Downscaling at 10km (CaRD10) Part 1--System Detail and Validation with Observations: Journal of Climate, v. 20, p. 5,527-5,552. National Oceanic and Atmospheric Administration, 2013, 2013 NOAA Coastal California TopoBathy Merge Project, National Oceanic and Atmospheric Administration, National Centers for Environmental Information database, accessed February 28, 2015 at
This work is part of on-going modeling efforts for California and the western United States. For more information on CoSMoS implementation, see
  1. How might this data set be cited?
    Hegermiller, Christie, Erikson, Li, and Barnard, Patrick, 20161020, Nearshore waves in southern California: hindcast, and modeled historical and 21st-century projected time series: data release DOI:10.5066/F7N29V2V, U.S. Geological Survey, Pacific Coastal and Marine Science Center, Santa Cruz CA.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -120.81115722553
    East_Bounding_Coordinate: -116.66931152258
    North_Bounding_Coordinate: 34.687068180405
    South_Bounding_Coordinate: 32.546444355161
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 01-Jun-2015
    Ending_Date: 30-Aug-2016
    publication date
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: Modeled nearshore wave time-series data in netCDF format
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a Vector data set.
    2. What coordinate system is used to represent geographic features?
      Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.00001. Longitudes are given to the nearest 0.00001. Latitude and longitude values are specified in Decimal degrees. The horizontal datum used is North American Datum of 1983.
      The ellipsoid used is Geodetic Reference System 80.
      The semi-major axis of the ellipsoid used is 6378137.000000.
      The flattening of the ellipsoid used is 1/298.257222.
      Depth_Datum_Name: North American Vertical Datum of 1988
      Depth_Resolution: 2.0
      Depth_Distance_Units: meters
      Depth_Encoding_Method: Explicit depth coordinate included with horizontal coordinates
  7. How does the data set describe geographic features?
    Nearshore waves in Southern California
    Nearshore wave parameter time series for hindcast (1980-2010), GCM historical (1976-2005), and GCM 21st-century (2012-2100) time periods (Source: U.S. Geological Survey)
    Nearshore wave parameters for validated hindcast, GCM historical, and GCM 21st-century time periods
    Significant wave height, period (peak and mean), and direction (peak and mean) at specified station locations (Source: Model-determined) Time-series data at 4,802 locations approximately 100 m apart along the 10 m bathymetric contour from Point Conception to the Mexican border. Descriptions of attribute variables for the data are contained in the header of each netCDF file.

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • Christie Hegermiller
    • Li Erikson
    • Patrick Barnard
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
    Erikson, Li
    U.S. Geological Survey, Pacific Coastal and Marine Science Center
    2885 Mission Street
    Santa Cruz, CA

    831-460-7563 (voice)

Why was the data set created?

These data are intended for policy makers, resource managers, science researchers, students, and the general public. These data are not intended to be used for navigation.

How was the data set created?

  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
    Date: 28-Feb-2015 (process 1 of 4)
    Obtained topobathymetric elevation data from Coastal California Topobathy Merge Project.
    Date: 01-Jun-2015 (process 2 of 4)
    Using topobathy data, generated grid bathymetry for wave simulations and identified nearshore station locations.
    Date: 01-Jun-2015 (process 3 of 4)
    Began wave simulations with Simulating Waves Nearshore, SWAN.
    Date: 01-Dec-2015 (process 4 of 4)
    Finished wave simulations and began analysis to identify nearshore wave parameters.
  3. What similar or related data should the user be aware of?

How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?
    Projected attribute values are model-derived wave parameters (significant wave height [Hs], period [T], and direction [D]) for historical and 21st-century time periods derived from the latest climate projections, and therefore cannot be validated against observed values. Hindcast (1980-2010) time-series data have been validated against wave buoy observations, showing Hs is modeled with a spatially-averaged skill value of 0.85 (RMSE = 14-40 cm), and T is modeled with a skill value of 0.65 (RMSE = 3.3-5.1 s). Hindcast RMSE for D ranges from 22-60 deg (skill not available for this variable).
  2. How accurate are the geographic locations?
    Data are concurrent with topobathymetric DEM locations.
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
    Dataset is considered complete for the information presented (as described in the abstract) and will be updated as necessary as improvements are developed. Users are advised to read the rest of the metadata record carefully for additional details.
  5. How consistent are the relationships among the observations, including topology?
    Data have undergone quality checks and meet standards.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints: none
USGS-authored or produced data and information are in the public domain from the U.S. Government and are freely redistributable with proper metadata and source attribution. Please recognize and acknowledge the U.S. Geological Survey as the originator(s) of the dataset and in products derived from these data.
  1. Who distributes the data set? (Distributor 1 of 1)
    U.S. Geological Survey - ScienceBase
    Denver Federal Center, Building 810, Mail Stop 302
    Denver, CO

    1-888-275-8747 (voice)
  2. What's the catalog number I need to order this data set?
  3. What legal disclaimers am I supposed to read?
    Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty.
  4. How can I download or order the data?

Who wrote the metadata?

Last modified: 29-Jun-2017
Metadata author:
Christie Hegermiller
U.S. Geological Survey, Pacific Coastal and Marine Science Center
2885 Mission Street
Santa Cruz, CA

831-460-7588 (voice)
Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

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