Interdecadal change in the South Asian summer monsoon rainfall in 2000 and contributions from regional tropical SST

The drying trend in the South Asian summer monsoon (SASM) area has been a focus of monsoon rainfall studies in the last two decades. However, this study reveals that a significant interdecadal change in the SASM rainfall occurred in approximately the year 2000. Obvious spatial inhomogeneity was a feature of this change, with increased rainfall over the southern part of the India–Pakistan border area that extends from the Arabian Sea, as well as in the western Bay of Bengal. Furthermore, there was decreased rainfall over the southern SASM and the western coast of the Indian Peninsula. Numerical experiments using CAM4 show that global SST changes can induce general changes in the SASM circulation consistent with observations. The tropical Pacific/Indian Ocean SST anomalies dominated the Walker and the regional Hadley circulation changes, respectively, while the descending motion anomalies over the southern SASM were further enhanced by the warmer tropical Atlantic SSTs. Moreover, the spatial inhomogeneity of this interdecadal change in the SASM rainfall needs further study.