Investigating the Mechanisms of Hydrological Impact Due to Drought-Flood Abrupt Alternation in the Upper Hanjiang River Basin, China

Abstract Drought-flood abrupt alternation (DFAA) is defined as a compound extreme event characterized by the rapid transition between drought and flood conditions within a short period, leading to significant ecological and socio-economic impacts. Currently, few studies have systematically investigated the interaction mechanism between meteorological and hydrological DFAA events using robust index. Consequently, this study optimized the DFAA index (DFAI) using both subjective and objective methods, and quantitatively assessed the correlation between meteorological DFAA and hydrological DFAA in the upper Hanjiang River basin (HJRB) through integrated statistical analysis and SWAT model simulations. The primary findings indicate that meteorological DFAA events exhibit distinct spatial heterogeneity, predominantly occurring in the eastern part of the basin, with flood-to-drought (FTD) events frequency surpassing drought-to-flood (DTF) events. There is a strong correlation between meteorological DFAA and hydrological DFAA, though their relationship is nonlinear across multi-scales. Statistical analysis reveals that long-term hydrological events are more distinctly driven by meteorological factors, whereas short-term events are significantly influenced by human activities. Model simulations further show that the decrease in the frequency of hydrological DFAA events and the shift of their dominant manifestation type from DTF to FTD are attributed to changes in precipitation patterns, which have also intensified their extremity. Anthropogenic factors have exacerbated the magnitude of long-term hydrological DFAA events while diminishing short-term ones, partially mitigating their shift from DTF to FTD. This study offers insights into hydro-meteorological risk and its implications for basin water resources management.