Spatial and Temporal Structures of Relationship Between Seasonal Mean Temperature and Rainfall in China

The interdecadal and interannual variation components of seasonal mean temperature and rainfall are extracted by applying spectrum analysis on monthly mean temperature and rainfall data of 160 stations during 1955—1998 in China. Evidence shows that the variances of interannual components are much larger than those of interdecadal parts, but it is the opposite while the variances are divided by their freedom degrees respectively, especially for temperature. In winter, most of the significant interdecadal variation areas lie in the northern half of China including Northeast China, North China and northeast part of Xinjiang. While in summer, the significant interdecadal variation areas locate in South China, Central China and Northwest China. As for the interannual variation of seasonal temperature, there are no significant areas both in winter and summer. In contrast with the seasonal temperature, the significant interdecadal and interannual areas of rainfall are fairly small and disconnected, among which two small patches of significant interannual variation in Shandong and Southeast China in winter are noticeable.It is implied in correlation analysis that the negative correlation between seasonal mean temperature and rainfall is remarkable in summer particularly over east of 105°E and south of 35°N of the main land, and it can be inferred that both anomalous hot dry and cool wet summer have more likelihood in most part of this region. For the purpose of verifying this point, observational station data are analyzed. The results present that 30 out of 44 years are either hot dry or cool wet summer in Yangtze Huaihe River Valley and South China, 21 out of 44 years in North China.Singular vector decomposing (SVD) are conducted to reveal the spatial and temporal features of the relationship between the two elements. It is indicated by the SVD modes that the two summer patterns are statistically significant in Yangtze Huaihe River Valley and South China. For years, both interdecadal and interannual time coefficients are negative, the rate of hot dry summer in Yangtze Huaihe River Valley is 6/8, and the rate of cool wet summer in South China is 5/8, while the reverse is true when time coefficients are positive, 6/7 cool wet summer in Yangtze Huaihe River Valley, and 4/7 hot dry summer in South China. The summer patterns occur out of phase in the two regions during the same year which is contributed by the negative correlation of summer mean temperature and rainfall on both interdecadal and interannual time scales.