Intergovernmental Panel on Climate Change (IPCC/AR5) mentioned that flood and storm surge will be more serious in lower zones caused by sea level. It is anticipated that intense typhoon will be formed stronger and it will bring flood and storm surge on the same time in Japan because of higher sea temperature. Although many studies have done on impacts on each flood and storm surge, few studies have done on a compound disaster involving these two events. To understand the impact of compound disaster, we try to estimate the damage cost in Japan for the compound disaster.
Flood and storm surge coincide as the compound disaster are selected considering damage in lower areas in Japan. We focus on low atmospheric pressure at typhoon because almost compound disasters selected are derived typhoon. The magnitude of the tide level and daily rainfall which can cause compound disasters are calculated from the relationship between annual minimum atmospheric pressure and tide level deviation, and between annual minimum atmospheric pressure and daily rainfall. The tide level data from 59 tide-gauge stations in Japan over 16 years, the daily rainfall data from 143 rain gauges in Japan over 51 years, and the atmospheric pressure data for each observation station are used for analyses on the tide level and daily rainfall. We distribute spatially the tide level and daily rainfall by means of Inverse Distance Weight (IDW) method. 2D non-uniform flow model expressing the inundation depth is calculated using daily rainfall distribution as input data and the tide level data on coastline in Japan as a boundary condition. Damage cost is estimated using inundation depth calculated by the above method and prices per unit of area calculated by each land use developed by the flood control economy investigation manual. Inundation depth and damage cost are calculated with one square kilometer mesh, with a land use inventory having 11 classifications including rice field, farmland, building site, golf course, main road site, forest, wasteland, other site, river and lakes, beach and sea area is used for the damage cost estimation.
The total damage cost in whole Japan for 50-year return period of compound disaster is 88 trillion JPY. The compound disaster damage costs of Tokyo, Aichi, and Osaka prefecture are higher than any other prefecture and the amount of damage cost in the three prefectures accounts for 33% of the total cost in Japan. Asset values of these prefectures are higher and most of their areas located on low altitude areas compared with the others. The damage cost by the Ise Bay Typhoon in 1959 which actually bought a compound disaster in Japan is compared and shows good agreement with this estimation.
Results show where government should invest intensively in disaster prevention by infrastructure in high-risk area to raise resistance to water disasters in Japan. This can support considering city planning based on the regional characteristics. Our result can contribute to flood control design and the efficient adaptation method against water disasters.