Oceanum Waddenzee NORA3 Wave Hindcast

February 2025

Dataset description

The Waddenzee NORA3 wave hindcast dataset provides high-resolution wave parameters for the Wadden Sea, a unique shallow tidal flat system along the Dutch and German North Sea coast (Figure 1). The Wadden Sea is characterised by extensive intertidal flats, barrier islands, and complex bathymetry that creates challenging conditions for wave modelling. Wave spectra are computed over a 30+ year period between 1993 and present using the SWAN (Simulating WAves Nearshore) third-generation spectral wave model.

This hindcast is distinguished by several specialized features for accurate shallow water wave modelling:

• High-resolution NORA3 winds: The NORA3 reanalysis from the Norwegian Meteorological Institute provides superior representation of coastal wind patterns compared to global reanalyses, with ERA5 gap-filling where needed.
• Calibrated water levels: Water levels combine tidal constituents from the Oceanum Waddenzee tide model with bias-corrected sea surface height from Glorys reanalysis, providing accurate representation of tidal modulation critical for shallow water wave dynamics.
• Tidal currents: Current velocities merge tidal constituents with Glorys reanalysis currents to capture wave-current interactions.
• High-resolution bathymetry: Bathymetry is derived from 20m resolution data from OpenEarth, combined with GEBCO in areas where local data was unavailable. This captures the complex tidal flat morphology essential for accurate shallow water wave modelling.

Spectral boundaries are provided by the Oceanum Western Europe NORA3 Wave Model. The modelling setup employs the ST6 source term parameterisations. Spectra are discretised into 36 directional bins and 43 frequency bins, covering a frequency range from 0.037 to 2.03 Hz with 10% logarithmic increments. The extended frequency range captures the short-period wind waves characteristic of fetch-limited shallow seas. The model features a high-resolution grid with approximately 500m resolution (0.008° x 0.005°).

The dataset provides hourly estimates for wave parameters (Table 2) including spectral quantities integrated over the full spectrum and for spectral partitions from the Watershed method. These data are stored over the entire grid at native resolution. Additionally, frequency-direction wave spectra are available at 710 sites distributed across the domain (see Figure 1).

Figure 1. Mean significant wave height from the Waddenzee NORA3 hindcast domain. The locations of 2D spectra hourly output are shown by the black dots. Depth contours are shown at 5m, 10m, 20m, and 50m.

Validation

The wave hindcast has been validated against in-situ wave observations from buoys within the Wadden Sea (Figure 2). The validation demonstrates good agreement between modelled and observed significant wave height across multiple stations, capturing both the magnitude and temporal variability of wave conditions in this complex shallow water environment.

Figure 2. Validation of modelled significant wave height (black) against observations (orange) at multiple stations within the Wadden Sea for January-February 2012. Station locations are shown on the map (left).

Data description

Table 1. Data description.

Linked Datamesh datasources

• Oceanum Waddenzee NORA3 500m hourly wave parameters
• Oceanum Waddenzee NORA3 500m hourly wave spectra

Integrated parameters gridded output

Integrated wave parameters are stored hourly over the domain at the native model resolution. Table 2 describes long names and units of the 24 gridded output parameters, including one wind-forced partition and one swell partition from the Watershed method.

Table 2. Gridded output parameters.

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