Especiall}' in eastern Asia, the climatological conditions are very different 

 from other continents and the above-mentioned formulae are not appHcable 

 by themselves. 



In eastern Asia evaporation is observed at few stations, and ample 

 material is not obtainable. Now the observational data are collected 

 as much as possible in Japan, Manchuria, China, and East Indies. 

 Through previous study we ascertain that the annual evaporation is 

 related not only to the temperature, but also to the amount of pre- 

 cipitation, but the mutual correlation is not the same with respect 

 to the individual regions. So we can express the annual amount of 

 evaporation E by the linear function of temperature t and precipitation P. 



E=a+6/— cP 



The constants a, b, and c are determined by the method of leagt squares 

 in each region, and the following results are obtained. 



Japan: E=790-f32-8^— 0-03P 

 Manchuria : E = 1375+50-7^— 0-09P 

 China: E=3506-117-7!!-040P 

 East Indies : E=449+29/— 0-13P 



Theoretically the arid boundary may be chosen where the amount 

 of annual evaporation equals that of the precipitation. But practically 

 the amount of evaporation measured by instruments in general use in 

 Japan and other countries is too much as compared with the real value. 

 Sometimes it reaches twice the evaporation from the field surface. 

 Moreover, a part of rain-water runs down into the ground and it is clear 

 that the precipitation equal to evaporation does not give the arid 

 boundary. However, as these details are not completely known, I 

 assumed temporarily that the arid boundary is located where the annual 

 amount of precipitation is half of the annual evaporation. Onty in the 

 East Indies, where the Wild's atmometer is used, the boundary is taken 

 where the annual amount of precipitation is equal to that of evaporation. 

 Thus the annual amount of precipitation P on the arid boundary line is 

 given by the following formula. 



Japan : P^387 + 15'8^ 

 Manchuria: P=206+18-5^ 

 China: P = 1463-49^ 

 East Indies: P=397+25-6^ 



So, if the actual amount of precipitation at any place is larger than the 

 calculated value P, it belongs to the humid climate and vice versa. 



For example, the calculated value P in the East Indies is 1,040 mm., 

 and actually no station belongs to arid climate. 



The whole of Japan also belongs to humid climate, while a part of 

 .Manchuria and China represents arid climate. The boundary line is 

 shown in the map. The northern half of China and the eastern part of 

 Manchurian mountainland belong to arid region. Actualty this boundary 

 line a grees well with the distribution of plants and geographical land- 

 scape — for example, the northern limit of rice-culti\'ation. 



124 



