Secular Variations of the Rainfall in Japan

Abstract

In order to study the secula r variations of various rainfall amounts quantitatively, the next three methods are taken into consideration;
a. Trend inspection based on rank correlational procedure.
b. Fitting the orthogonal polynominals to secular variation.
c. Statistical quantities showing variability and per s istence.
Yearly, monthly and special rainfall amounts were statistically analysed by using the electronic computer, and we obtained the following main results through geographical comparison of the statistical quantities:
(i) Over the whole area of Japan, there are more widely increasing regions than decreasing regions.
(ii) Conspicuous increasing trends can be seen at Kylisha and Shikoku districts.
(iii) Both increasing and decreasing trends are seen disorder at To-hoku and Hokuriku districts, and rather apparent increasing regions i n snowfall amount are scattered over these districts.
(iv) Decreasing trend can be seen at Kanto district for any kinds of rainfall amounts on the whole.
As a result, the q u alitative explanations hitherto put forward by several authors have been revised quantitatively and more in detail, and some of them are more or less corrected in this paper.