| 22 Jul 2025
Developing a Coastal Hazard Prediction System in Ice-Infested Waters, Part 1: High-Resolution Regional Wave Modeling in The Estuary and Gulf of St. Lawrence
Abstract. This study is the first of a two-part paper that summarizes the development of a prototype coastal hazard prediction system providing short-term (+48 h) forecasts of the total water level (TWL) at 50 m resolution for the province of Quebec, Eastern Canada. In this first part, the implementation of the offshore wave model component of the system, which is a regional 1 km-resolution WAVEWATCH III™(WW3) configuration for the Estuary and Gulf of St. Lawrence (EGSL), is presented and discussed. The configuration is forced by high resolution atmosphere, ocean and sea ice forecasts provided by Environment and Climate Change Canada (ECCC) and includes a state-of-the-art parameterization of wave propagation and attenuation in sea ice that has been tuned with observations from the EGSL. Performances are assessed against wave data collected over a two-year period during which the forecasting system was running operationally, and against historical storm data using a model hindcast. Results demonstrate reasonable forecast skills both for normal and extreme wave conditions during ice-free periods with errors ranging from 15 % to 31 % of the mean wave height. However, when sea ice is present, performances are drastically reduced, primarily due to inaccuracies in the predicted ice fields at spatial scales over which wave energy typically dissipates in sea ice.
Review of “Developing a Coastal Hazard Prediction System in Ice-Infested Waters, Part 1: High-Resolution Regional Wave Modeling in The Estuary and Gulf of St. Lawrence”
This paper reports on the implementation of the wind wave component of a forecasting system for coastal hazard. As such, it is an interesting paper to read. As stated by the authors, much progress is still needed for the proper representation of the complex interactions between atmosphere, waves, currents and sea ice. It is a bit worrisome that the wave predictions were quite well off the observations and potentially not providing much guidance. One could wonder whether an ensemble approach should be used to sample the large uncertainty in the sea ice conditions (i.e. what would the wave conditions be if the sea ice conditions were to be a lot less)?
Some comments and questions:
Table 1: what is the justification for using ST3 as most WW3 these days are using ST4 or ST6?
117: WW3 employs logarithmically frequencies: f(n) = r * f(n-1)
with f(1)=0.05 and f(25)=1.1 Hz would imply r=1.1375, which is a bit unusual. Is it what was used? More commonly used is r=1.1, which would make the frequency discretisation slightly less coarse and probably more appropriate for low energy, short fetch conditions. You would have had to increase the total number of the frequencies to 34 but noting that the set-up is for high resolution forecasts, it might have been relevant.
193: was there any quality control applied to the observations?
193: what is the frequency used for the calculation of the mean wave period (Tm2)? Is it consistent with what the model is using? From figures B1 and B2, it does look to me that the model and the prediction have used different frequency range when estimating Tm2. Not using the same frequency range will results in a systematic bias between the two quantities.
215: are you sure about your definition of MBE (A1)? From Figure 7, it looks to me that biases should be negative, i.e. Observations are more often larger than Prediction. Hence while you could say that here is an underestimation of the highest waves by the model.
Minor correction:
Table 1:
WAM Cycle 4 -> WAM Cycle 4 (ecWAM) (i.e. ST3 in WW3 5.16 is based on ECMWF modifications of the original WAM Cycle 4)
wave breaking -> bottom induced wave breaking
119: 3h -> 3-hourly
127: is the forecast output also 3-hourly?
Figure 10: wave direction -> mean wave direction?