Problem of Climatological Water Balance in Japan

Abstract

In this paper, the amount of potential evapotranspiration has been calculated in variohs places of Japan after THORNTHWAITE's suggestion. Comparing these figures to those of precipitation, we can. obta in the climatological balance table ran in Tab. 1 and Fig. 1. Everywhere in Japan, the amount of precipitation presents fairly large surplus than that of evapotranspiration, distribution of which is sho wu in Fig. 2. The amount of surplus is larger along the coasts of Japan Sea and Pacific, where annual surplus is above 1, 000mm, while in drier regions such at S:touchi, Central Highland, NW-Kantô, AbukumaKitakami Valley and -Hokkaidô, it is less than 7501ilm. The former regions fairly coinside with regions, where flood and wet damages occur most frequentry and the latter coincides with drought areas of Japan. Seasonal changes of the monthly mount of water.surplus at various places are studied., and 6 types of the annual change have been classif ied: see Figs. 3 and 4. 1. 1. Japan Sea type……… The water surplus maximum occurs only in winter. II. 2. Kyûsyu type ……… he prime maximum occurs at Bai, -u season and th.1.o Secondary maxima in spring and autumn. II.3. Setouchi type……… The spring m .aximu_Yn predominates and the autumnal maximum, accompanied by typh.oo:n, is no-it clear. II. 4. Nankai (South Sea) type ……… 'The prime maximum occurs at the period of autumnal typhoons and one of the secondary maxima can be seen in. spring, but another, that is the Bai-u maximum, is not so distinct. II. 5. North-Pacific, type……… The maximum of Bai-u season can not be recognized in northern parts of the Pacific-side in Japan. II. 6. Central Japan type ……… The three maxima of about the same grade can be recognized: in spring Bai-u and typhoon seasons. This type appears in Kinki, TOkai, and Central Highland. We have, then, researched on the geographical distribution of monthly y amount of water surplus, which is shown in Figs. 5, and 6. The maximum. amount of the change of water storage is shown in Fig. 7, together with the months when storage changes happen. We can understand that the driest region in Japan is Setouchi District and the next is Eastern Kant& an the basins of Central Highland. And storage change occurs from May to October. In earlier seasons, it appears in the northern parts, then extends, to the south and its distribution becomes the broadest in August. Moreover, we can calculate the climatic wet-and dryness in various places of Japan according to the next formula: moisture ratio. (_??_) Geographical distribution of this ratio in Japan is shown in Fig. 8, from which, we can classify two areas: -Most per fumid area…… Japan Sea coast region, the South Sea coast region. Relatively and area…… Setouchi, Central basins, NW-Kantô, Kitakamni Valley and Hokkaidô.