Multiscale Dynamic Mechanisms of Drought‐Flood Abrupt Alternation Events in the Yangtze River Basin

Abstract

Drought‐flood abrupt alternation (DFAA) events have become more frequent under global warming, posing increasing risks to society and ecosystems. Using the standardized weighted average precipitation index combined with run theory, we identify DFAA events across the Yangtze River Basin (YRB) from May to September during 1961–2022. A total of 1,097 DFAA events were detected, including 89 regional events. Both types of DFAA events feature rapid transitions of less than 4 days and show frequency and enhancing intensity, particularly after 2000. Regional events occur most frequently in the middle and lower reaches of the YRB. To investigate the underlying mechanisms of regional events, the canonical transfer framework based on the multi‐scale window transform was used. Intensified positive North Atlantic Oscillation and weakened midlatitude westerlies enhance Ural blocking (UB), whose peak occurs 2–4 days before DFAA onset and creates key precursor stages. Meanwhile, intraseasonal‐scale available potential energy associated with UB propagates downstream toward the YRB. This energy transfer enhances baroclinic instability and gradually establishes a baroclinic structure over the basin. During DFAA onset, the intensified baroclinic instability combines with the convergence of cold‐dry air from the north and warm moisture transported by the westward‐extended western Pacific subtropical high. This interaction triggers an abrupt shift from drought to heavy rainfall. This study clarifies how large‐scale circulation patterns coordinate across time scales to produce DFAA in the YRB. The identified early‐stage signals provide valuable guidance for improving the prediction of these high‐impact events.