Hydrological drought-flood abrupt alternation across mainland China and its influencing factors

Abstract. Drought-Flood Abrupt Alternation (DFAA) is a compound extreme event characterized by a rapid transition from drought to flood. It can pose substantial risks to society and environment. Although the impacts of DFAA are closely linked to variations in surface and subsurface water availability, most existing studies have relied primarily on meteorological indicators. In this study, we diagnosed hydrological DFAA (H-DFAA) events across mainland China from 1980 to 2019 using daily total runoff from a multi-model ensemble of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP). We further investigated the relationship between H-DFAA and meteorological DFAA (M-DFAA), the latter derived from meteorological indicators. Moreover, the key influencing factors of the transition rate and intensity of H-DFAA were identified using explainable machine learning approaches. Results showed that H-DFAA occurred most frequently in spring, with hotspots in northern basins, contrasting with the prevailing focus on summer and southern basins from previous M-DFAA studies. H-DFAA and M-DFAA showed good temporal consistency in southern basins, whereas snowmelt and antecedent drought conditions led to large timing mismatches in northern basins. The transition rate and intensity of H-DFAA were mainly influenced by precipitation in humid southern basins, but by snowmelt, antecedent drought conditions in northern basins. Other land surface characteristics including vegetation fraction and average elevation could also impact the transition rate and intensity of H-DFAA across different basins and seasons. These findings highlight the distinct spatiotemporal characteristics and potential driving mechanisms of H-DFAA, and underscore the importance of incorporating hydrological processes into DFAA assessment and risk management.