Abstract
The middle and lower reaches of the Yangtze River Basin (MLYRB) are prone to Rapid Flood‐Drought Transition (RFDT) due to uneven spatiotemporal distribution of precipitation. In recent decades, such events have shown a marked interdecadal increase, posing serious threats to disaster prevention and mitigation. To reveal the interdecadal characteristics and underlying physical mechanisms, this study employs the daily standardised precipitation index (SPI) and standardised soil moisture index (SSI) to investigate RFDT events in the MLYRB during 1961–2022. Results indicate a significant interdecadal rise in summer RFDT frequency after 2000: 9 events occurred during 1961–2000 (0.22 events/year), compared to 11 events during 2001–2022 (0.50 events/year), representing a 127% increase in annual occurrence. This shift is closely linked to interdecadal variability of influencing factors. Before 2000, RFDT events were primarily governed by the East Asia‐Pacific (EAP) teleconnection pattern, with intraseasonal (20–60‐day) symmetric phase transitions systematically shifting circulation and moisture configurations from flood to drought conditions. After 2000, the modulating influence of the EAP teleconnection weakened due to increased asymmetry in its oscillations, whereas the Western Pacific Subtropical High (WPSH) extended westward, with enhanced intraseasonal oscillation in its western sector. This enhanced intraseasonal geopotential height variability guides meridional displacement of the WPSH, directly regulating moisture transport and becoming the dominant mechanism for increased RFDT frequency since the 21st century. Additionally, the westward extension and intensification of the background WPSH prolonged drought duration in post‐2000 events. This study reveals the physical mechanisms of interdecadal RFDT variability in the MLYRB, particularly the shift in dominant circulation systems, thereby advancing our understanding of interdecadal changes in regional climate extremes.