Dynamic Changes in Quasi‐Biweekly Variability Drive Increased Extreme Rainfall and Whiplash Events Over Asian Monsoon Regions

Abstract Persistent rainfall extremes and whiplash events in the Asian monsoon region are closely linked to quasi‐biweekly variability, which has intensified significantly over the past four decades in southern China, the northern Bay of Bengal, and northwestern South Asia. Multiple reanalyses indicate that regional quasi‐biweekly rainfall variability increased by 12%–44% in the recent two decades relative to the earlier two. This intensification is driven mainly by dynamical changes in vertical velocity perturbations, while thermodynamic increases in mean moisture play a secondary role. The strong dynamical influence also accounts for much of the spread in historical simulations from CMIP6 and CESM2‐LENS. Only when thermodynamic moistening outweighs this dynamical uncertainty do models consistently project stronger quasi‐biweekly variability under future scenarios. These findings highlight the central role of quasi‐biweekly circulation in monsoonal rainfall extremes and the need to improve its representation in climate models.