Distinct Future Changes in the Midlatitude and Low-Latitude Connections between the South and East Asian Summer Monsoons Projected by CMIP6 Models

Abstract The South Asian summer monsoon (SASM) and the East Asian summer monsoon (EASM) are connected through two plausible pathways: a midlatitude wave pattern and low-latitude coherent water vapor transport. To reveal their different responses to global warming, this study investigates their future changes using the moderate- and high-emissions Shared Socioeconomic Pathway 2-4.5 and 5-8.5 (SSP2–4.5 and SSP5–8.5) experiments from 26 models of phase 6 of the Coupled Model Intercomparison Project. The results show that the midlatitude connection is projected to be weakened, while the low-latitude pathway is projected to be strengthened in both scenarios, with stronger changes in SSP5–8.5. The weakening midlatitude pathway in the future is likely attributed to the weakened climatological westerly jet stream. The weakening Northeast Asia anticyclone in the midlatitude wave train suppresses water vapor transport and vertical motions to northern China, resulting in a weakened rainfall relationship between northern China and the SASM region. The low-latitude pathway is anticipated to be strengthened, probably due to the strengthened Maritime Continent summer rainfall. The strengthening western North Pacific anticyclone in the low-latitude moisture transport pathway increases the horizontal water vapor transport to the Yangtze River Valley, but its northward shift suppresses local vertical motions, leading to a weakened relationship between the Yangtze River Valley and SASM rainfalls in both SSP2–4.5 and SSP5–8.5. Through separately analyzing the rainfall patterns associated with the two pathways and the underlying physical mechanisms, this study enhances our understanding of the future changes in the SASM–EASM relationship under global warming. Significance Statement The South Asian summer monsoon (SASM) and the East Asian summer monsoon (EASM), which significantly influence Asian climate, are connected through a midlatitude wave pattern and low-latitude coherent water vapor transport. This study highlights the distinct future changes in these pathways. The midlatitude wave pattern is expected to be weakened, reducing the relationship between northern China and SASM rainfalls. Conversely, the low-latitude pathway will be strengthened, leading to a weakened relationship between the Yangtze River Valley and SASM rainfalls due to suppressed vertical motions. This study provides a valuable insight into the future change in the SASM–EASM relationship and is helpful for comprehending the connection between extreme events in the two monsoon regions and to project their future changes.