Increased water vapor transports of atmospheric rivers around the western flank of the North Pacific High since the 1980s

Abstract During the previous decade, intense and widespread heavy rainfall has occurred occasionally in midsummer over East Asia around the western flank of the North Pacific High. Such extreme events share the common feature of a synoptic-scale band of intense water vapor transport called an atmospheric river (AR). However, using observational data, it is difficult to detect trends in the intensity of ARs owing to the complex effects of internal climate variability and diversity in synoptic weather patterns. Herein, using the technique of self-organizing maps to delineate their effects, we found an increasing trend of AR-related water vapor transport of 8.3 ± 2.3% between 1981 and 2022. Enhanced low-level southerly and southwesterly winds transported more water vapor over the Korean Peninsula and Japan. This trend of the atmospheric circulation is closely related to the decadal-scale oscillation over the Pacific Ocean and resultant enhancement of the North Pacific High. In addition to dynamic intensification of ARs, robust increase in water vapor content associated with rising air temperature also contributed to AR intensification. These results suggest that the trend of increase in AR intensity could continue over coming decades, although with increasing fluctuation on the decadal time scale.