Multidimensional Asymmetry and Basin-Scale Evolution Patterns of Drought–Flood Abrupt Alternation Across China’s Nine Major River Basins

Under global warming, compound extreme events such as Drought–Flood Abrupt Alternation (DFAA) are becoming increasingly common, yet the structural asymmetry and spatial dynamic evolution between Drought to Flood (D–F) and Flood to Drought (F–D) processes remain under-researched. Using high-resolution daily precipitation data spanning 1961 to 2022 from nine major river basins in China, DFAA events were identified via the Standardized Weighted Average Precipitation (SWAP) index coupled with run theory, and their evolution was analyzed using multidimensional spatiotemporal metrics. Our results reveal a spatial frequency and severity mismatch, where southern basins exhibit high frequency occurrences dominated by slight to moderate events, whereas northern and inland basins experience lower overall frequency but a significantly higher proportion of severe events. Spatial polarity asymmetry is evident, with D–F events dominating nationwide and exceeding 74% in northern and inland basins, while southern humid basins exhibit a more balanced D–F/F–D structure. Temporally, D–F processes involve prolonged moisture accumulation, whereas F–D processes manifest as short-lived post-rainfall moisture deficits. Based on risk trajectories, basins were categorized into four impact patterns: highly oscillatory pattern, intensifying pattern, long-cycle accumulative pattern, and baseline pattern. Ultimately, regional DFAA risks are governed by polarity asymmetry and non-stationary evolution rather than absolute frequency alone, providing a critical scientific basis for basin-specific disaster mitigation strategies under climate change.