We discussed effectiveness and limitation of a risk index of natural disaster for the countries of the world, World Risk Index, which is defined as the product of exposure and vulnerability, and discussed its effectivenesses and limitations. We emphasized necessity of a concept of a natural disaster risk index for forty seven prefectures of Japan from the viewpoint of rational countermeasures against natural hazards based on scientifically reliable index. We conducted a provisional calculation of susceptibility, a intermediate index consisting the vulnerability of the risk index, and discussed essential points and issues of the evaluation system of the risk index.

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 Remote sensing is one of the effective methods for grasping situations of damaged areas due to natural disasters such as earthquakes, tsunamis, heavy rains, and so forth as quickly as possible. Generally, the locations are determined by subtracting the satellite image which was observed before the disaster, “before-image”, from that observed after the disaster, “after-image”. In this study, however, we tied to obtain the locations of slope failure areas by using only “after-image” with the aid of digital elevation model. We analyzed seventy-two areas where slope failures occurred due to earthquake and heavy rain, and found that the proposed method is useful although the process is relatively simple.

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