Abstract
　Three climatic indices which are the sum of monthly precipitation amounts for June, July and August, the sum of precipitation during Baiu seasons and total numbers of days on which rainfall is less than 5mm in the period between June and August are used to examine the dry summer of Fukuoka.
　The statistic analysis of data reveals that severe dry summer occured nine times and moderate dry summer four times for 99 ycars (1890−1988). Based on grey system theory we set up the model of GM (l, 1) which is one-dimensional and first rank-differential equation. To check the model, estimations and predictions of two types of time series are conducted in grey system theory and compared with the results of Fourier analysis.

【キーワード】：夏季干ばつ，灰色システム，灰色予測モデル
Key words: dry summer, grey system, prediction model

*鳥取大学大学院連合農学研究科
United Department of Agricultural Science, Graduate School of Tottori University
**山口大学農学部
Faculty of Agriculture, Yamaguchi University
***九州大学農学部
Faculty of Agriculture, Kyushu University