Dominant patterns of summer rainfall anomalies in East China during 1951-2006

The dominant patterns of summer rainfall anomalies in East China were studied using Empirical Orthogonal Function (EOF) analysis. The results indicate that after the late 1970s, the first and second dominant patterns switched. During the period before the late 1970s, the spatial pattern of the first (second) dominant mode was the "Yangtze River pattern" (the "South China pattern"), but this changed to the "South China pattern" (the "Yangtze River pattern") after the late 1970s. This decadal change in the dominant patterns resulted from a significant decadal change in summer rainfall over South China after the late 1970s, i.e., a negative phase during 1978-1992 and a positive phase during 1993-2006. When the decadal variation of rainfall in East China is omitted from the analysis, the first and second dominant patterns represent the "Yangtze River pattern" and the "South China pattern", respectively. These results suggest that when decadal variation is included, the rainfall in China may be dominated by one mode during certain periods and by another in other periods. For the interannual variability when decadal variation is excluded, however, the first and second modes can be easily distinguished, and their order has been stable since at least 1951.