More Frequent Extreme Precipitation on the Asian Monsoon Fringes Driven by Evolving Extratropical Planetary-Scale Circulations

Zhenyu You, Yi Deng, Yi Ming, Jaeyoung Hwang

In recent decades, the fringes of the Asian summer monsoon, such as Pakistan and Northeast China, have become hotspots of extreme precipitation. Although such increases are often linked to thermodynamic changes in a warming climate, the dynamical drivers behind these trends, particularly the systematic role of extratropical circulations, remain poorly understood. This study identifies the large-scale atmospheric circulation patterns responsible for intense summertime rainfall in Northeast China and Pakistan. Clustering analysis reveals that the recent increase in intense precipitation is driven by a distinct shift in the preferred Rossby wave pathways over Eurasia. Dynamical analysis with an idealized model indicates that this shift is driven by an evolving upper-tropospheric mean flow which modifies atmospheric instability and wave propagation. These results highlight the need to understand the origins of extratropical background flow changes to improve projections of regional precipitation in a changing climate.