A novel multivariate index for identifying drought-flood abrupt alternation events across China

Study Region Nine Major River Basins in China Study Focus Drought–flood abrupt alternation (DFAA) events pose a serious threat to the sustainable development of natural, socioeconomic, and ecological systems. To accurately identify DFAA events, this study develops a novel index that integrates multiple types of drought, namely the EMDFI, and applies it to characterize the spatiotemporal patterns and evolution of DFAA across China’s nine major river basins. New Hydrological Insights for the Region The EMDFI was validated against historical disaster records and demonstrates strong capability in accurately identifying DFAA events. DFAA, drought-to-flood (DTF), and flood-to-drought (FTD) events exhibit pronounced spatial heterogeneity. The Southeast Rivers Basin shows the highest frequencies of DFAA, DTF, and FTD events (33.062, 13.389, and 19.673 events, respectively), as well as the most severe FTD (1.013). The Huai River Basin experiences the most severe DFAA and DTF, with corresponding values of 0.998 and 1.048, respectively. In the Songliao, Haihe, Yellow, Huai, Northwest Rivers, and Southwest Rivers basins, DFAA events are predominantly driven by DTF transitions. These findings provide a scientific basis for climate change adaptation and optimized water-resources allocation across the region.