地学雑誌

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Saigyo (1118-1190), one of the most famous poets in Japan, composed a poem on cherry blossoms referring his death, which was collected in his anthology called “Sankashu”. The meanings of the poetry are as followers;
It is to be desired that I should meet my end under the full bloomed cherry trees bathed in the full moon light of “Kisaragi” month.
The poem was likely versed in the later period of his life, though there is no records left to ascertain when it was composed. The lunar-solar calender imported from Tang and noted by the name of “Senmei-Reki” was used at that time.
The dates of the 15 th of “Kisaragi”, the second month in the ancient calendar, are converted to about a month or so later dates in the present solar calendar, though different year by year.
The cherry blossoms poem by Saigyo must be based on his experiences continuing several years or more, not on an extraordinary experience of one special case. At present the cherry trees come into full bloom generally in the first or second decade in April in the middle part of Japan. (see Table II) The solar calendar dates converted from the 15 th of “Kisaragi” seem to be remarkably earlier than the present flowering seasons of cherry trees.
Many authors have presented the hypothesis that a Little Climatic Optimum should exist in the period from the end of the XII century to the beginning of the XIII century, and, as seen in Fig. 3 (b), the last decade of Saigyo's life (1181-1190) coinsides to the peak of the winter character curve in England given by H. H. Lamb.
The percentage ratio of the snowy days to the whole precipitation days from November to March (henceforth “snowy days ratio”) is entitled to be a reliable index for the heat and cold during the cold season in the ancient times (see Fig. 2) as well as at present. (see Fig. I)
The snowy days ratios computed by the data in “Gyokuyo”, the diary written by Kanezane Kujo (1149-1207) give the estimations of every year warmth and coldness during the later part of Saigyo's life. (see Table 2) The averaged snowy days ratio in the period of (1180-1184) is only P=11.5%, being much smaller the whole period average of “Gyokuyo” P=21.4%.
Descending from Koya Mountain, Saigyo removed his dwelling to Ise Province in the spring of 1180 and lived there until his departure of his long journey to Ou provinces in the fall of 1186. Ise Province is located south east from Kyoto at a distance of about 110 Km. and the climate is respectably warmer in winter than Kyoto or Koya Mountain.
The full bloom dates of cherry trees (D) at Kyoto are computed by substituting the snowy ratios (P) to the tentatively adopted equation
D=0.32 P+3 … (1)
and the estimated full bloom dates at various places where Saigyo lived are compared. with the converted solar calendar dates of the 15 th of the second month in the formar calendar. (see Table I) According to my opinion, Saigyo's famous poem on cherry blossoms in “Sanka-shu” is concluded to be composed at the end of his stay at Ise Province, for the peak of warmth during the Little Climatic Optimum around 1200 which was experienced in the warm regions of Ise can only make it possible that Saigyo could admire the cherry blossoms in the full moon light of “Kisaragi” month. I hope that the above conclusion might give some gleams for the solution of the questionable problems about the time when the compilation of “Sanka-shu” was completed.
If it is admitted to use the equation (1), the average flowering season of cherry trees at Kyoto in the period of “Gyokuyo” (1167-1200) in which P=21.4% is estimated to be April 10, five days earlier than now. Consequently it is presumed that averaged mean air temperatures in February and March at that times should be about 2°C higher than today.

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