Extreme Sea Levels and Their Attribution for the Canadian Pacific Coast From a Baroclinic Regional Ocean Model and Tide-Gauge Data

The existing operational storm surge model for the Canadian Pacific coast is barotropic without coupling with tides. Here a baroclinic ocean model, which includes tides, storm surges, intra-seasonal, seasonal, and interannual variations, is developed to reproduce coastal sea levels in the northeast Pacific from 1993 to 2020. The model results are validated against observations at tide-gauge sites, demonstrating overall good skills for tides and non-tidal sea levels. The Gumbel distribution is applied to derive extreme sea levels from hourly sea level anomalies. The model-based extreme sea levels agree approximately with the observation-based ones. For the 100-year return period, modeled total extreme sea levels range from 2.14 m at Victoria Harbour to 4.43 m at Queen Charlotte City, and modeled non-tidal extreme sea levels from 1.02 m at Bella Bella to 1.78 m at Queen Charlotte City. On average, the model-based values underestimate the 100-year return level by 0.18 m for total extreme sea levels and by 0.23 m for non-tidal extreme sea levels. Both the model- and observation-based results reveal that the storm surge at periods less than 10 d accounts for 60% of the 100-year non-tidal extreme sea level, and the intra-seasonal, seasonal, and interannual variations account for 40% of it. The present study improves coastal sea level modeling and model-based extreme level estimates. Moreover, this study also demonstrates for the first time that the intra-seasonal to interannual changes contribute substantially to extreme sea levels and that El Nino can enhance this contribution on the Canadian Pacific coast.