Interdecadal Variation of Early Spring Rainfall Over the Southeastern Edge of the Tibetan Plateau

This study investigates the interdecadal variation in early spring rainfall over the southeastern edge of the Tibetan Plateau (SEETP) during 1979-2015 and its possible causes using mainly Asian Precipitation-Highly-Resolved Observational Data Integration Toward Evaluation daily precipitation data set, ERA5 reanalysis data and the atmospheric general circulation model ECHAM6. A significant interdecadal change in early spring rainfall over the SEETP occurred with its node around 1998/1999. The early spring rainfall over the SEETP was heavier in 1979-1998 than in 1999-2015, reflecting a reduction in moderate and heavy rain during the early spring. The covariability of the Pacific Decadal Oscillation (PDO), Atlantic Multidecadal Oscillation (AMO), and Indian Ocean Basin Mode (IOBM) is an important driver of the interdecadal decrease in early spring rainfall over the SEETP. When the PDO is in a cold phase, and the AMO and IOBM are in positive phases, an anomalous cyclone is excited over the Bay of Bengal-western Pacific in the lower to middle troposphere. Anomalous easterly winds on the north flank of the anomalous cyclone lead to the interdecadal decrease in early spring rainfall over the SEETP by reducing water vapor transport from the Indian Ocean and producing divergence over the SEETP. This diagnosis of the key physical process linking the associated sea surface temperature anomalies with the interdecadal variation in early spring rainfall over the SEETP is supported by numerical experiments.