INTERANNUAL VARIATIONS OF RAIN SPELL DURINGPREDOMINANT SUMMER MONSOON OVER CHINAFOR RECENT THIRTY YEARS
Guo Qiyun Wang Jiqin (Institute of Geography, Academia Sinica)
Firstly, by using the normal decade rainfall data for eastern China to analyze the seasonal change of rainfall. Investigation shows that the maximum rainfall zone usually stagnated for some days in South China when it moved from south to north, and did so in Changjiang Basin and North China respectively. These three periods of stagnation coincided roughly with the time interval of predominant monsoon in above mentioned regions. But in Changjiang Basin the length of stagnating period was much shorter than other two regions and even so a slight movement of maximum rainfall zone observed again. Secondly, the rain spells for South China, Changjiang Basin and North China were decided by using the pentad rainfall data year by year from 1951 to 1979. The begin- ning and ending dates, intermissions and persistences of rain spells were obtained. The rainfall sum for each raiii spell was calculated too. It is found that the charcteristics of rain spells varied from one year to another obviously. The beginning dates of rain spells experienced the biggest interannual variations, especially in South China. The varia- tions of rain spells of one region rarely correlate with another. Thirdly, an analysis of long period rain spell variations shows that the trend was more predominant in Changjiang Basin. In general, the beginning of rain spell was earlier, the duration was longer and the rainfall sum was much bigger in 1950s in Changjiang Basin and South China. On the contrary, the beginning of rain spell was later and the length of rain spell was shorter, the rainfall sum was smaller in Chang- jiang Basin in 1960s. At the same time, the beginning of rain spell was earlier and the persistence of rain spell was longer, but the rainfall sum did not increased much in North China. In 1970s, in both South China and North China the rain spells started later and ended later also. In the last decade the rainfall sum at Changjiang Basin has a moderate value between the 1950s and1960s.