中文摘要：

本文利用黄河中游及其分区1955～2002年盛夏干旱指数资料，采用最大熵谱分析和小波分析方法，对黄河中游盛夏干旱变化的周期性特点和各分区不同干旱等级之间的遭遇概率进行了统计分析。结果表明：①中游盛夏干旱的显著周期是12年，其次是准3年（2．8年）；②各分区显著周期不尽相同，其中泾渭洛河和汾河为3年（2．8年）和2．1年，龙花间和河龙间为8年和10年（9．6年）；③黄河中游不同分区同时发生大旱或特旱的概率比较高，而同时发生涝的概率却比较小。

英文摘要：

The periodicity and encounter probabilities of midsummer drought in the middle reaches of Yellow River were analyzed using the methods of maximum entropy spectrum analysis and wavelet analysis according the midsummer drought index of the middle reaches of Yellow River and its sections from 1955 to 2002. The results showed that. （1） The most prominent period of midsummer drought index in the middle reaches of Yellow River was twelve years, the next was qusi- three- year （two point eight years）. （2） The prominent period was variational in different section. Qusi- three- year and 2.1 years were the obviously period in Jing-Wei-Luo and Fen River valley, and the period of eight years and ten years were notable in inter-zone from t-Hekou to Longmen and inter-zone from Longmen to Huayuankou. （3） The probability of appearing heavy or special drought in the four sections of the middlereaches of Yellow River at the same time were very high, and the probability of flood in the four sections of the middle Yellow River at the same time was almost impossible.