Assessment of compound occurrence of storm surge and river flood in Ise and Mikawa Bays, Japan using a framework of atmosphere–ocean–river coupling

Abstract

Abstract This 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 (one-way coupling). 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. Second, the time difference between the storm surge and discharge at the estuary (Δ T ) was investigated, assuming six typhoons with different tracks and similar distributions of intensity and precipitation using Typhoon Hagibis (2019) as a case study. The Δ T was highly positively correlated with the length of the river channel (correlation coefficient: 0.90). Moreover, the smaller rivers were more prone than large rivers to simultaneous storm surges and high river flow. The average Δ T for the smaller rivers was 180.4 min (normalized S.D. = 0.31) with a minimum of 15 min in the most severe case, while the average Δ T for the large-scale rivers was 614.1 min (normalized S.D. = 0.39). We clarified that the storm surge and high river flow occurred simultaneously (within 15 min) in the most severe river case (Yagyu River). These results infer that small rivers have a more significant impact on the co-occurrence of storm surge and high-river flow than large-scale rivers.