Evolution of drought-flood abrupt alternation events in Chongqing based on the daily dry-wet abrupt alternation index

Drought-flood abrupt alternation events of 34 meteorological stations in Chongqing City were identified by the daily dry-wet abrupt alternation index（DWAAI）, which can accurately reflects the suddenness and alternation of the events. Based on the actual situation of Chongqing City, the range of DWAAI values for drought-flood abrupt alternation events at different levels were determined and the spatiotemporal characteristics of the frequencies of these events were analyzed. The results showed that the drought-flood abrupt alternation events in Chongqing City were predominantly characterized by a transition from drought to flood, accounting for 85% of the total drought-flood abrupt alternation events. These drought-flood events mainly occurred during April-September, and the multi-year average cumulative frequency was 22.64 times, with moderate and severe events accounting for 11.7% and 2.9%, respectively. Spatially, drought to flood events occurred frequently in the western, central and northeastern regions, with no significant trend in frequency change. Whereas flood to drought events mainly happened from July to September, and the multi-year average cumulative frequency was 5.60 times, with mild and moderate events accounting for 92.9% and 7.1%, respectively. From spatial perspective, flood to drought events were frequent in the southeastern, central and the west part of northeastern regions（such as Kaixian）, and the frequencies of the regions listed above generally showed an increasing trend. The research results can provide a theoretical basis for enhancing water security and strengthening drought prevention, flood resistance and disaster reduction in Chongqing and neighboring regions.