Coastal storm surge amplification by wave radiation stress: The case study of 2015 Typhoon Soudelor in East Taiwan

This study investigated the coastal storm surges along the east coast of Taiwan during the passage of Typhoon Soudelor in 2015, which was a representative typhoon event making landfall from eastern Taiwan. A new coupled surge-tide-wave model was developed to simulate storm surges, tides, and wind waves from offshore to nearshore regions. The hindcast simulation was driven by the global reanalysis winds, and the input wind data and the simulation results were validated using the observations from tide gauges and marine buoys. The simulation results captured the spatial and temporal variations of storm surges, predicting the peak water levels and their arrival times accurately. Comparisons between the model simulations with and without considering waves revealed that the wave-induced radiation stresses contributed significantly to the peak surges, amplifying them by 30–50% at several tide gauge locations along the east coast of Taiwan. The intensity of radiation stress gradients was found to be 20–80 times larger than that of wind shear stresses and sea-level atmospheric pressure gradients within the surf zones at the time of Typhoon Soudelor's landfall in Taiwan. Moreover, the overall contribution of radiation stresses to storm surges was found to amplify storm tides by 23.3% to 31.5% along the east coast of Taiwan.