2023 Volume 79 Issue 17 Article ID: 23-17042
The present and future compound coastal flooding risk by storm surges and river floods at the river mouth of Japan’s three major bays was diagnostically evaluated based on the d4PDF climate projection. The number of extreme cases in which large storm surges and large river discharges occur by the same typhoon tends to increase slightly in the future. On the other hand, the time difference between the peak storm surge and the peak river discharge in the future climate tended to shorten by about 0.7 hours. In addition, such shortening of storm surges and river flood peaks will be significant for the rivers with the larger time difference under the present climate. The future changes in peak-time shortening are caused by the shortening of the start of the flow to the maximum flow. Finally, the relationship between drainage area and the peak time difference was examined for the top 10 cases of high river discharge in each river. The results showed that the variability of each case tended to decrease in the future. This result suggests that storm surge and flood peaks will likely overlap even when the typhoon track is not the worst.
