Evolutionary characteristics and association analysis of meteorological and hydrological drought-to-flood abrupt alternations in the Upper Yangtze River basin

To address water resource management challenges in the Upper Yangtze River basin under changing climate, this study investigated drought-flood abrupt alternation events based on monthly precipitation and runoff data from 1959 to 2022. Meteorological and hydrological drought-flood abrupt alternation indices were calculated to identify the occurrence frequency, intensity, and intra-annual distribution characteristics of events. The Mann-Kendall trend test was applied to evaluate the temporal evolution, while correlation coefficients, mutual information coefficients, and factor importance analysis were used to assess the associations between meteorological and hydrological drought-flood abrupt alternations. The results indicate that: (1) From 1959 to 2022, long-term meteorological and hydrological drought-flood abrupt alternation events in the Upper Yangtze River basin exhibited consistent occurrence frequency and intensity. However, short-term hydrological events occurred 56% less frequently than meteorological events, with a more pronounced intra-annual concentration during the flood season; (2) Both long-term meteorological and hydrological drought-flood abrupt alternation events during the flood season displayed a tendency toward “flood-to-drought” trend. This is consistent with the “drought-to-flood” trend in June and “flood-to-drought” trend in August . (3)The long- and short-term hydrological drought-flood abrupt alternations are influenced by meteorological drought-flood abrupt alternations of different sub-basins. Large-area sub-basins (Yalong River, Jialing River, Xiangjiaban-Cuntan interval, and Upper Jinsha River basin) exhibited strong correlations between long-term meteorological and hydrological drought-flood abrupt events, whereas associations between short-term events were stronger in sub-basins near the Three Gorges Reservoir (Jialing River, Xiangjiaba-Cuntan interval and Cuntan-Three Gorges interval basin). The research results can provide important scientific basis for flood control and disaster reduction and adaptive water resource management in the upper Yangtze River basin.