Spatiotemporal patterns and hydroclimatic contributions associated with drought–flood abrupt alternation in the Yangtze River Basin

Study region Yangtze River Basin of China Study focus This study examines the spatiotemporal patterns, seasonality, periodic variability, and hydroclimatic contributions of drought–flood abrupt alternation (DFAA) in the Yangtze River Basin during 1961–2023. Drought-to-flood (DF) and flood-to-drought (FD) events are identified using a standardized DFAA index (DFAAI) constructed from consecutive monthly standardized precipitation evapotranspiration index (SPEI) values. Trend, hotspot, spectral, and SHapley Additive exPlanations (SHAP) analyses assess their frequency, intensity, evolution, and associated predictors. New hydrological insights for the region DFAA frequency and intensity exhibit distinct spatial patterns, indicating that the recurrence and severity of rapid water-balance reversals are not spatially uniform across the Yangtze River Basin. High-frequency areas occur mainly in the middle–lower basin and lake regions, exceeding 10 events per decade, whereas the strongest events cluster along the Sichuan Basin margin. Basin-mean linear trends are weak, but DFAA variability strengthened after 2000. DF events span June–October, while FD events concentrate in July–September and show stronger synchronization among sub-basins, reflecting different monsoon-season pathways of moisture recovery and depletion. DF and FD frequencies show recurrent 3–5-year variability, whereas intensity contains longer-period components. SHAP results indicate that rapid precipitation and humidity changes are most consistently associated with the initiation of water-balance reversals, while temperature and radiation conditions contribute more strongly to their intensity, especially for FD. Large-scale circulation indices mainly modulate the background climate state.