近畿地方における梅雨の長期変動傾向

Abstract

Duration of the Baiu season and the Baiu precipitation amount in Kinki district, CentralJapan, were estimated for one hundred historical years with the use of ancient documents. Add-ing the results to the instrumental observation records, long-term fluctuation of the Baiu wasshown for two hundred years, from the latter half of the 18th century to the present. Durationof the Baiu season has fluctuated with some variation width from year to year. As for the endof the season, it comes in the first ten days of July in some periods. But it appears in thelast ten days of July in other periods. Those periods, when the end of the Baiu is delayed, correspond to the cool summer periods in Northeast Japan. In Central and West Japan, heavy rains and flood damages frequently occurred in these periods.Secondly, the long-term fluctuation of the Baiu precipitation amount at Osaka, located onthe middle of Kinki district, was examined. Ten year avarage precipitation amount has fluctu-ated between 200 mm and 450 mm the two hundred years. However those abnormal climaticconditions that exceeded the values of instrumental observation records did not appeared in thehistorical periods.Lastly, the long-term fluctuation patterns of the annual precipitation amount were comparedwith that of the Baiu precipitation amount. There is meaningful correlation between the twovalues. Therefore, by reconstructing the Baiu season weather conditions, long-term fluctuationof the climate can be estimated from the viewpoint of dry and wet conditions.