Abstract: Drought-flood abrupt alternation (DFAA), as an extreme compound event, exerts far greater impacts on natural and social systems than individual drought or flood events. Based on CMIP6 data, population data, and GDP data, this study projected the evolutionary trends of DFAA and changes in population and GDP exposure in the Pearl River basin from 2021 to 2100 under three shared socioeconomic pathways (SSPs). The results are as follows. The frequency of DFAA events exhibited a non-significant upward trend from 1962 to 2020. In the future, the frequency of flood-to-drought alternation will be significantly higher than that of drought-to-flood alternation. The frequency of drought-to-flood alternation will decrease with the increase in emissions, while the frequency of flood-to-drought alternation will be the highest under high-emission scenarios. Except for the long-term period (2061?2100) under SSP1-2.6, both the frequency and intensity of drought-to-flood alternation show a decreasing trend compared to the baseline period. In the near-term period (2021?2060), the frequency of flood-to-drought alternation under the three SSPs is lower than that in the baseline period, while it rises in the long-term period. Under three SSPs, the population exposure to drought-to-flood alternation in the Pearl River basin presents a temporal trend of “differentiation in the near-term period and common increase in the long-term period”, with GDP exposure showing an overall upward trend. Spatially, such exposure is mainly distributed in the Pearl River Delta region. The population exposure to flood-to-drought alternation decreases in the near-term period compared to the baseline period but increases in the long-term period. The GDP exposure to flood-to-drought alternation also follows a trend of “differentiation in the near-term period and common increase in the long-term period”, and spatially, it gradually spreads from the downstream to the midstream and upstream regions.

Key words: Pearl River basin, CMIP6, Shared Socioeconomic Pathway (SSP), Drought-flood abrupt alternation, Exposure