Intensification of East Asian Summer Rainfall Interannual Variability in the Twenty-First Century Simulated by 12 CMIP3 Coupled Models

The authors examine the projected change in interannual variability of East Asian summer precipitation and of dominant monsoonal circulation components in the twenty-first century under scenarios A1B and A2 by analyzing the simulated results of 12 Coupled Model Intercomparison Project phase 3 (CMIP3) coupled models. Interannual standard deviation is used to depict the intensity of interannual variability. An evaluation indicates that these models can reasonably reproduce the essential features of the present-day interannual variability in both East Asian rainfall and the rainfall-related circulations. The models project an enhanced interannual variability of summer rainfall over East Asia in the twenty-first century, under both scenarios A1B and A2. Over the East Asian summer rain belt, 10 of the 12 models under scenario A1B and 9 of the 10 models under scenario A2 show enhanced variability in the twenty-first century relative to the twentieth century. The multimodel ensemble (MME) results in increased ratios of interannual standard deviation of precipitation averaged over this region of about 12% and 19% under scenarios A1B and A2, respectively. Furthermore, it is found that the interannual variability is intensified much more remarkably in comparison with mean precipitation. Two circulation factors, the western North Pacific subtropical high (WNPSH) and East Asian upper-tropospheric jet (EAJ), which are closely related to the interannual variability of East Asian summer rainfall, are also projected by the models to exhibit enhanced interannual variability in the twenty-first century. This provides more evidence for the enhancement of interannual variability in East Asian summer rainfall and implies intensified interannual variability of the whole East Asian summer monsoon system. On the other hand, the relationships of East Asian rainfall with the WNPSH and EAJ do not exhibit clear changes in the twenty-first century under scenarios A1B and A2, and there are great discrepancies in the changes of the relationships among the individual models.