Assessment of Compound Flooding Risk in Ise and Mikawa Bays, Japan Using a Framework of Atmosphere-Ocean-River Coupling

Abstract The present study evaluated the compound flood risk of 11 different-sized rivers in the estuaries of the Ise and Mikawa Bays, Japan, using an integrated framework of atmosphere-ocean-river developed in this study. First, the framework was developed by incorporating the river channel into a coupled model of surge-wave-tide to include the interaction of the storm surge runup and river flow. In addition, the framework was validated by the Typhoon Trami (2018)-induced meteorological field, discharge, and storm surge with high accuracy. Then, the time difference between the storm surge and discharge at the estuary (TDSD) was investigated assuming six typhoons with different tracks and similar distributions of intensity and precipitation using Typhoon Hagibis (2019) as a case study. It was found that the TDSD reveals a high positive correlation with the length of the river channel (correlation coefficient: 0.90). Also, the smaller rivers were more prone to simultaneous storm surge and high river flow. The river with the smallest TDSD average in 6 cases of sensitivity experiments was 70 minutes, and it was clarified that the storm surge and high river flow occur simultaneously (within 15 min) in the most severe case (the smallest TDSD case). As a result, it was found that the small- and medium-sized river with a standard deviation of 49.5 minutes has a small TDSD regardless of the typhoon track, resulting in a higher risk of compound flood in comparison to the large-scale rivers with that of 102 minutes.