Analysis of drought-flood abrupt alternation in China from 1981 to 2024

Study region The study encompasses the entire territory of China, which has been classified into seven climate regions. Study focus This study developed the daily-scale Standardized Drought-Wet Abrupt Alternation Index (SDWAI) to identify and assess Drought-Flood Abrupt Alternation (DFAA) events. Using the modified Mann-Kendall method, Sen’s slope estimator, the moving t-test, the spatiotemporal trends and evolutionary features of DFAA events across China were systematically examined. New hydrological insights for the region: This study found that during 1981–2024, the DFAA events exhibited distinct regional and seasonal characteristics at both interannual and annual scales, with a significantly increasing frequency, featuring a spatial pattern of high frequency in the southeast and low in the northwest, and summer witnessed the most frequent and severe events. A shared mutation occurring in 1991 and 1992 showed a national wet shift, interannual variability and spatial coverage of DFAA expanded, and the high-frequency areas showed characteristics of northward movement and southward expansion after each mutation. The gradient of spatial anomaly percentage of average precipitation showed moderate and less significant correlation with frequency, acting as a potential influential factor. Meanwhile, a preliminary national threshold of ±0.6 is proposed for application across different arid and humid regions.