Abstract: Drought-flood abrupt alternation (DFAA) refers to a rapid transformation between droughts and floods, which poses great threats to agricultural production and human security. This study, based on the monthly scale magnitude index of DFAA, analyzes four types of historical and future DFAA events in the Yangtze River basin. A time-varying function for the magnitude of DFAA is constructed using a sliding window approach, revealing the future changes in DFAA risk. Shared socio-economic pathways are integrated to quantify the impact extent of changing risk of DFAA on population and economy. The results show that in historical periods, the hotspots of the DFAA events were mainly distributed in the middle and lower reaches of the basin, with drought-flood and flood-drought events occurring 10 - 12 times per decade, and drought-flood-drought and flood-drought-flood events occurring 3 - 4 times per decade. Drought-flood-drought and flood-drought-flood events are projected to significantly increase in the future for the whole basin, and parts of it will experience a growth of approximately seven times. For the historically recorded 50-year DFAA events, the probability of their occurrence will increase by 5 to 10 times in the future, and the population and economy of the basin will be significantly affected.

Key words: drought-flood abrupt alternation, standardized precipitation evapotranspiration index, Coupled Model Intercomparison Project in the Sixth Phase, population exposure, Yangtze River basin