夏季旱涝的演变规律,近年来已为许多气候工作者所注意。

Based on a chronicle list of droughts, excessive rainfalls and floods (903 B.C.-1909 A.D. ) complied from the materials in classics, chronicles and annals, along with the meteorological records of Shanghai (1875-1962 )，the historical trends of droughts and excessive rainfalls in the Lower Yantze are studied. Using certain intensity cri- terions, the events are classified and return periods are analysed. It appears that there may exist some kind of thousand-year cycles, each with three intervals of different charac- teristics, which show fairly good correspondence with the solar activities. An outlook of the trend in the coming 30-years is made, tentatively.