Recent Opposite Trends of Atmospheric Rivers Over East Asia and Western North Pacific Driven by the Pacific Decadal Oscillation

Atmospheric rivers (ARs) in East Asia have garnered increasing attention for their crucial roles in understanding extreme precipitation events and regional hydrological cycles. Here, we investigate the summer AR frequency over the East Asia-western North Pacific region (EA-WNP) during 1959-2022. Interestingly, the results show that the AR frequency over the two regions experienced opposite variations, with the boundary between them at around 135 degrees-140 degrees E. On interdecadal timescales, such variations are mainly synchronized with a zonal dipole pattern characterized by cyclonic (anticyclonic) anomalies centered to the northwest of Taiwan and anticyclonic (cyclonic) anomalies centered to the southeast of Japan. This interdecadal dipole pattern is induced by interdecadal changes in the western North Pacific subtropical high under different Pacific Decadal Oscillation (PDO) phases. Particularly, the internal variability accounts for about 77-90% of the observed trends in high response areas. The displacements of ARs are also consistent with the opposite trends of precipitation over EA-WNP. ARs exert a dominant influence on the precipitation trend in the WNP region but a weaker contribution to the precipitation trend in the EA region, which reflects the different impacts of ARs on EA and WNP precipitation. These results indicate that the PDO has the potential for predicting EA-WNP ARs on interdecadal timescales, and the opposite AR trends are crucial in understanding the complexity of precipitation over the EA-WNP region. Atmospheric rivers (ARs) are long, narrow corridors of intense water vapor transport, and considered a crucial source of extreme precipitation events and floods over coastal regions. Previous research has revealed southward-shifting trends of ARs over East Asia (EA) in recent decades. However, the possibility of opposing AR trends within different areas of the entire EA and western North Pacific region (EA-WNP) has not previously been considered. In this study, we examine the summer AR frequency over EA-WNP based on reanalysis data during the past six decades. The results show that EA-WNP ARs have experienced opposite interdecadal variations and formed opposite trends between EA and the WNP during specific periods. Further analysis reveals that these interdecadal shifts of ARs can be explained well by a zonal dipole pattern modulated by the interdecadal change in the western North Pacific subtropical high under a strong influence of the Pacific Decadal Oscillation. Moreover, such AR variations have caused opposite precipitation trends in EA-WNP and contributed differently to the formation of the distinct precipitation regimes in EA and the WNP. These findings provide insights into the decadal prediction of ARs and their diverse roles in shaping regional precipitation variations over the EA-WNP region. Summer atmospheric rivers (ARs) over East Asia and the western North Pacific (EA-WNP) have experienced opposite trends in recent decadesOpposite AR trends are modulated by a zonal dipole pattern, which correlates closely with the Pacific Decadal OscillationSuch AR variations lead to opposite precipitation trends and contribute differently to the precipitation regimes between EA and the WNP