Abstract: The spatial distribution, temporal evolution and periodic variation character of the beginning date of rainy season in Yunnan were studied by using of EOF (Empirical orthogonal function) and maximum entropy spectral analysis method based on daily precipitation data at 124 rainfall stations from 1971 to 2007. The relationship between different distribution patterns of the beginning date of rainy season and monsoon was also analyzed. The results showed that the first main spatial distribution feature was that the whole provinces beginning date of rainy season was unanimously earlier (or later) than normal time, the second feature was reverse spatial distribution between the middle, namely the eastern and the southern and western of Yunnan. The obviously 3-5 years oscillation period existed in the first main spatial distribution. The obviously 3-4 years oscillation period existed in the second main spatial distribution feature. There was obviously correlation between the beginning date of rainy season and the OLR over the Bay of Bengal region and the South China Sea region in May in the same year. The intensity indexes of South Asia monsoon and the South Sea monsoon were of great indicative significance in the the beginning date of rainy season in Yunnan province.

Key words: The beginning date of rainy season, EOF, South Asia Monsoon, South China Sea Monsoon