Spatiotemporal Evolution and Directional Asymmetry of Drought–Flood Abrupt Alternation Events Across China's Hydroclimatic Zones

ABSTRACT The identification of drought–flood abrupt alternation (DFAA) events has progressively evolved from conventional threshold‐based and empirical index approaches toward multivariate, probabilistic, and process‐oriented frameworks, with increasing emphasis on dry–wet transition rates, joint rarity, and directional asymmetry. Nevertheless, substantial scope remains for developing unified identification schemes at large spatial scales and for systematically characterizing their spatiotemporal evolution. Based on monthly hydroclimatic data across China during 1961–2024, this study developed a reverse‐Copula‐based framework to identify D–F and F–D events, classify their intensity, and analyze their spatiotemporal evolution. The results show that DFAA events in China exhibit clear spatial heterogeneity, with high‐occurrence areas mainly distributed in the Eastern monsoon region, climate transition zones, and topographically complex areas. Mild and moderate events dominate the overall pattern, whereas severe and extreme events show more localized clustering. The number of events increased by approximately 22.5% after 2000 reflected not only in higher event frequency but also in a shift of the intensity structure toward medium‐ and high‐intensity events. D–F and F–D events show evident directional asymmetry, and their dominant direction varies across climate zones and decades. These findings provide a basis for identifying compound hydroclimatic extremes, assessing regional drought–flood hazards, and supporting climate‐change adaptation.