Chapter 6 Climate change adaptation and disaster risk reduction experiences in Japan

Japan is an island arc that sits in the monsoon region, and is under the influence of warm and moist air masses in summer and cool air masses in winter. The moisture that is taken in the lower leaves of the air masses over the sea is poured on the country by typhoons in summer, by snowfall in winter, by the “Bai-u Front” (in Japanese) in June and July, and by depressions and fronts in all seasons. Owing to Japan's slender shape and complicated landform, aerial differences in climate are great. Japan is located on the eastern edge of the monsoonal region of Asia, and its climate varies according to seasonal and regional conditions. Typically, heavy rains occur in various parts of the country, both during the rainy season in June and July and during the typhoon season from August to October. This precipitation is predominantly in the form of locally specific temporary downpours. In winter, the northern part of the country usually receives heavy snowfall that causes prolonged floods in spring from the melting of snow. The average amount of precipitation is 1,800mm (70 inches) a year. This is two or three times the amount received in other areas of the same latitude. In the southern Pacific coast areas, rainfall amounts to 4,000mm (160 inches). Precipitation in Tokyo is twice as much as other large cities in western countries. Some 50–60% of the annual precipitation in the Pacific coast of Japan is concentrated from June to October. Artificial changes in natural environments are rapid and large, accompanying the great increase in economic activity and exploitation (Nakano, Kadomura, Mizutani, Okuda, & Sekiguchi, 1974). Although the country's 10% of land area is flood prone, about 50% of the population lives in floodplains and almost 75% of the property is concentrated in the floodplains (JWF, 2006).