ANNUAL MARCH OF WATER ECONOMY IN JAPAN

Abstract

In the present paper, the authors discussed the resume of the water economy in various drainage areas in Japan (Fig. 1), comparing calculated amounts of water surplus with those of observed run off in each month. (1) Patterns of the annual march of monthly amounts of water surplus, which are given by differences between evapotranspiration and precipitation in each month, are distinguished into five major types in Japan. Namely, (I) Japan Sea coast-Tohoku-Hokkaido type (snow covered area type), (II) Tokai-Kanto type, (III) Nankai type, (IV) Setouchi-Kinai type, , (V) Kyushu type (Fig. 2). They, coincide with the division of the, precipi-tation resume. (2) Annual amount of the water surplus (specific run off) reaches about 2, 000mm in the southeastern part of Kyushu, Shikoku, Kii and a part of Japan Sea coast (Eig, 2). (3) Comparing the water surplus With observed run off by monthly value, the resumes of water storage in Japan are grouped roughly into two main types. One is snow covered, and the other is non-snow covered area type. (4) Even in the months of snow cover, some parts of the water surplus run off in the same manner as the months of no snow cover. However greater part of them remains as snow cover until later months. The ratio of the amount of melted snow to that of remaining one may be determined by the snowfall, rainfall and mean temperature of the average Value in the drainage area. Therefore, the water surplus becomes larger than run off in April in the drainage of much snow cover (e. g. No. 58, 61 in Fig. 3), and lower temperature drainage (e. g. No. 80, 83 in Fig. 3). (5) In the Bai-u season (June) the water surplus is remarkably greater than the run off, and the reverse case occurs in July. It is more predominant in Kyushu and slightly appears in the Pacific Sea coast and San-in district (Fig. 3). This maximum of the dif-ference between water surplus and run off is related to the prcipitation density in June (Fig. 4). (6) In the Typhoon season, the difference between water surplus and run off is not so clearly seen as in Bai-u season. (7) On the relation between monthly amount of water surplus and run off, the Thornthwaite's formula _??_