ABSTRACT Frequent drought‐flood abrupt alternation (DFAA) events in the Yangtze River Basin (YRB), characterized by complex formation mechanisms and limited predictability, pose a prominent challenge in climate research. A daily‐scale DFAA index is developed to enhance event identification accuracy by coupling dual signals from precipitation and soil moisture in this study. The selected 86 DFAA events from 1961–2023 are classified into two distinct spatial patterns: an Eastern type affecting the lower reaches and a Northern type influencing the northern middle reaches of YRB. The multi‐scale analysis demonstrates that DFAA alternation periods are primarily driven by 10–30‐day intraseasonal oscillations (ISOs), while the maintenance of drought and flood phases relies on 30–90‐day ISOs. However, during the alternation phase, Eastern‐type events are governed by upper‐troposphere dynamical processes, manifested through energy dispersion from the high‐latitude Rossby wave trains that drive rapid reversal of the 10–30‐day geopotential height over East Asia, accompanied by eastward‐propagating upstream westerly anomalies promoting westward extension of the jet stream over Japan, ultimately establishing strong upper‐level divergence over the key region and triggering the alternation to flood conditions. In contrast, Northern‐type events are predominantly controlled by low‐level processes, where 10–30‐day scale cyclonic circulation intensifies rapidly through lee‐wave forcing from the Qinling–Daba Mountains during its southward migration, triggering low‐level convergence and ascent that facilitate precipitation development. During the drought or flood phase, both types exhibit baroclinic structures over the key region, and the Eastern type primarily relies on eastward‐propagating 30–90‐day Rossby wave energy over the subtropics, whereas the Northern type is influenced by converging wave energy transported from both mid‐high latitudes and the subtropical region. This study provides a scientific basis for understanding the mechanisms of extreme hydrological events in the basin and improving extended‐range forecasting capabilities.
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