<p>A recent decadal-scale decline in precipitation has led to an intensification of drought events on the northern plateau of the Greater Mekong Subregion (NGMS), and the impact of these droughts has extended to agricultural lands along the middle and lower reaches of the Mekong Basin. To reveal the primary drivers of this reduction in precipitation, this study investigates decadal-scale variations in summer precipitation patterns over the NGMS. Our findings suggest that a dual mechanism associated with the Atlantic Multidecadal Oscillation (AMO) exerts a significant influence on summer precipitation dynamics over the NGMS. Firstly, the warm phase of the AMO induces a succession of high- and low-pressure systems across Eurasia at the 200-hPa level. Subsequently, the AMO-induced high-pressure anomaly over the northeastern flank of the South Asian High (SAH) leads to an anomalous anticyclone, which directly reduces northeastward water vapor transport over the NGMS. Secondly, the AMO contributes to the decadal-scale decline in summer precipitation over the NGMS by indirectly inducing warming in the northern Arabian Sea (AS). There is a notable correlation between the warming trend in the northern AS and precipitation in both the northern AS region and northwestern India. Subsequently, the SAH is strengthened and expands towards the southeast via Rossby wave responses triggered by precipitation-induced diabatic heating over the northern AS and northwestern India. Consequently, the easterly anomaly and descending motion intensify over the NGMS, leading to a significant decadal-scale reduction in summer precipitation. Numerical experiments support the role of this dual AMO mechanism in driving the observed decadal-scale decline in precipitation over the NGMS.</p>