Rain/temperature quotient (RQ) was calculated using monthly weather data for the growing period in order to take into consideration effects of seasonal variation in air temperature and rainfall on fruit production. The RQ dependence of yields of peach and Japanese pear in major fruit producing prefectures was approximately expressed by quadratic equation. It was found that the maximum yields of peach and Japanese pear are obtained at nearly 6 and 8 of RQ values, respectively.
A new agroclimatic index—climatic suitability index (CSI)—was introduced to evaluate agroclimatic suitability of individual prefectures for fruit cultivation. CSI was defined as a growing period mean of the deviation of monthly RQ from RQmax which is the RQ at the maximum yield of fruit. Linear relationship was found between long-time average of fruit yield and CSI for major fruit producing prefectures, showing that CSI can be used to evaluate the agroclimatic suitability of each prefecture for fruit cultivation. Weather data were treated to make clear the spatial distribution of CSI over Japan. Major producing areas of peach and Japanese pear were found to locate in the area with CSI above 70-80. CSI distribution map is also applied to evaluate regions suitable for the cultivation of grape (European, North-China, and American species) apple, cherry, persimmon, chestnut, and so on.
