THE ARID BOUNDARY IN EASTERN ASIA 



By EiiCHiRO FuKui, Japan 



Ik order to consider the effects of precipitation upon practical problems 

 the absolute amount of precipitation alone is not satisfactory. Especially 

 from the agricultural and pedological point of view, precipitation excess 

 or precipitation minus evaporation has most significance. On the other 

 hand, the evaporation is remarkably influenced by the temperature, so 

 that the precipitation and the temperature are the most important 

 factors to determine the boundary between the arid and himiid regions. 

 For this purpose many formulae involving the precipitation and 

 temperature have been found. Although these formulae apparently are 

 of different types, we can transform them into the same functional 

 expression. 



W. Koppen expressed the dry limit by the precipitation and temp- 

 erature. Annual precipitation r (cm.) on the boundary line which 

 separates the stepp climate from the humid climate is given by the 



empirical formulae 



y = 2 (/ + a) 



where t is the annual mean temperature at the station and a is a numerical 

 constant. 



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