Drought–flood abrupt alternation (DFAA) is one of the remarkable manifestations of the summer monsoon anomaly at the subseasonal scale and can result in severe damage. This study identified and analyzed DFAA in terms of streamflow in the Poyang Lake catchment over the last 50 years based on a DFAA index (DFAAI). The study also investigated the intra-annual distribution characteristics and long-term tendencies associated with DFAA, as well as the relationship with precipitation patterns. A statistical analysis showed that drought-to-flood events in the Poyang Lake catchment generally occur in March and April, while flood-to-drought events occur in July and August. A Mann–Kendall test indicated a long-term decreasing trend in DFAAI in March and April and a slight increasing trend in July and August; however, the trends were not statistically significant. Flood-to-drought events occurred more frequently than did drought-to-flood events at the decadal scale, especially in the 1960s and 1970s. The particular distribution of precipitation in the Poyang Lake catchment mainly determined the occurrence patterns of DFAA events, but intensive human activities are also significant factors that have decreased and mitigated DFAA disasters since the 1980s in the Poyang Lake catchment.

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