Drought to Flood Abrupt Alternation Events Across Monsoon Region in China: Characteristics, Mechanisms, and Crop Exposure

Abstract Climate change is altering the frequency and intensity of hydroclimatic extremes, increasing the likelihood of drought to flood abrupt alternation (DTFAA) events which creates compound risks. Here, we identify DTFAA events across the monsoon region of China (MRC) during May–September from 1961 to 2023 using the daily Standardized Weighted Average Precipitation index. We identify 3,575 DTFAA events, with most transitions occurring within 1–2 days and a modest maximum in June. Generally, DTFAA frequency and intensity in MRC increase significantly at rates of 0.29 times decade⁻¹ and 0.26 decade⁻¹, respectively, with high frequencies concentrated in the middle and lower Yangtze River Basin, southern coastal China, and parts of North and Southwest China. Dynamically, governed by jet-waveguide interaction, the transition initiates with high-latitude easterly anomalies anchoring upstream blocking and the westward-extending subtropic high priming baroclinicity. Subsequently, the intensified and westward-extending subtropical jet establishes a mid-latitude meridional potential vorticity gradient conduit, routing trapped energy in blocking downstream to drive deep dynamic suction and moisture convergence, unleashing the abrupt flooding. Furthermore, crop exposure is crop-specific heterogeneous: maize and wheat show extensive high-exposure belts, whereas rice exposure is more fragmented; maize exhibits significant increases in both frequency and intensity exposure during 2000–2019. These results demonstrate that DTFAA events in the MRC arise from coordinated large-scale circulation and moisture-transport processes and that their agricultural consequences are strongly crop and region dependent, providing a dynamical and impact-oriented framework for improving monitoring, prediction, and adaptation to rapid hydroclimatic transitions.