中文摘要：

利用黄河中游陕县站和永定河下游卢沟桥站逐日平均水位记录，以首次涨水超过0．64m作为汛期建立的标志，在“侯”尺度下重建了黄河以及永定河汛期开始时间距平序列，黄河中游序列开始于1919年，永定河下游开始于1912年。研究时段内，黄河中游平均入汛时间在7月5-10日、永定河在7月16-20日。相比黄河中游，永定河入汛时间比较稳定，汛期开始时间基本维持在6月底7月初，而黄河中游波动非常大，最早在3月份就入汛，最晚在10月份才进入汛期。而二者的入汛时间距平序列都与夏季风强度序列成反相关关系，即在夏季风强的阶段，入汛时间偏晚；夏季风弱的时候则偏早。结果表明：夏季风的强度影响着我国南北雨季的开始时间，夏季风强的年份，我国南方地区雨季开始时间提前，北方雨季开始时间推迟；在夏季风弱的年份，则相反。

英文摘要：

In this study, we reconstructed the time series of flood season onset date anomalies under pendate scale. A water level rise of 0.64 m marks the beginning of a flood season. This daily average water level records are obtained for Shanxian in the middle reach of the Yellow River and Lugouqiao Bridge in the lower reaches of Yongding River. The records start respectively in 1919 and 1912 for the Yellow River and Yongding River. During the study periods, the flood season usually started between July 5 and July 10 in the middle reach of the Yellow River, and between July 16 and July 20 in the Yongding River. The starting date is found to be more stable in the Yongding River comparing to the middle reach of the Yellow River. This is due to the fact that the rainy season is very much regular in late June or early July in the lower reach of Yongding River. However, the rainy season in the middle reach of the Yellow River showed a great deal of fluctuation which is as early as in March and in October as the latest. Both the time series of flood season onset date anomalies are inversely correlation with the intensity series of summer monsoon. It means that when the summer monsoon is strong, the beginning time of flood season is early; and the initinal time become late when the summer monsoon is weak. The results showed that the strength of summer monsoon have influence on the beginning time of rainy season in north and south of China. When the summer monsoon is strong, the beginning time of rainy season in south of China is early what in north of China is late; When the summer monsoon is weak, it reverse