Numerical simulations on inundation due to storm surge by scenario typhoons for structural design were carried out for ports along the three major bays of Japan assuming some different levels of sea level rise as impact of climate change, in order to evaluate the inundation risk due to storm surge for each of the ports. In addition, parametric study of scenario typhoons with different size were carried out, and the worst case of typhoon for each of the ports in these three bays was uncovered.
Storm surge in a closed sea area with shallow depth tends to be larger than that in an open sea area. Tokyo Bay, Ise Bay, and Osaka Bay, which have hinterlands with high density of population and property and are called the three major bays of Japan, are more closed and shallower than most other sea areas in Japan. Ports generally have wider waterside land of seawalls. Inundation risk in ports due to tsunami and storm surge is higher. Therefore, there is a high risk of inundation due to storm surge in the ports along these bays.
The Japanese government required local governments to make and publish hazard maps which show estimated inundation areas due to the worst case scenario of storm surge in May, 2017. The national government issued a manual for making the hazard maps to propose the worst case scenario in July, 2017. The hazard maps are under construction by the local governments.
The hazard map manual proposes the common condition of scenario typhoon which causes the worst case scenario of storm surge; the central pressure of the typhoon is 910 hPa: its radius of maximum wind speed, 75 km: its travel speed, 73 km/h. The central pressure of the scenario typhoon is the same as that of the Muroto Typhoon in 1934, which has the lowest central pressure at hitting the main island of Japan. The radius and travel speed of the scenario typhoon are the same as those of the Typhoon Vera in 1959, which has the second lowest central pressure at landfall on Japan since the Japan Meteorological Agency (JMA) started to record statistically meteorological observation in 1951. The radius and travel speed of Typhoon Vera were larger than those of Typhoon Nancy in 1961 which has the lowest central pressure at landfall in the meteorological statistics of JMA.