Analyzing the Evolution of Droughts and Floods During the Flood Season in the Yangtze River Basin and the Three Gorges Reservoir Area from 1470 to 2022

Abstract As an important economic region in China, The Yangtze River economic belt encountered a historically rare successive drought in 2022. Here even appeared a phenomenon of anti-dry during flood season, which significantly hindered the economic development in the belt. Thus, there is an urgent need to reveal the evolution pattern of drought and flood in the basin. This study analyzed the 553-year historical records of drought and flood levels at 12 representative stations located across the upper, middle, and lower reaches of the Yangtze River basin, and the Three Gorges Reservoir area. Based on the conventional judgment standard of drought and flood level, the sequence of drought and flood level during the flood season was constructed with “Yearly Charts of Dryness/Wetness in China for the last 500 years Period” and precipitation from May to September in 1961–2022 at the 12 stations in the region. The analysis revealed a normal distribution of drought and flood occurrences during the flood season, ranging from grade one to grade five in the area, with approximately 52–60% of the time experiencing normal conditions (grade three) and 2–4% being classified as drought (grade five) or flood (grade one) condition. From 1470 to 2022, there were distinct alternating periods of drought and flood during the flood season in the Yangtze River Basin, upper reaches, middle reaches, lower reaches, and the Three Gorges Reservoir area. The frequency of severe flood and flood events increased significantly in the 19th and 20th centuries, while the frequency of severe drought and drought events sharply rose in the 20th century. Within the 553 years, there were 13 flood years and 24 drought years in the Yangtze River Basin, with drought years occurring more frequently than flood years. Moreover, the upper, middle, and lower reaches of the basin experienced more frequent occurrences of droughts and floods compared to the entire basin. Evolutions of droughts and floods in the Three Gorges Reservoir area were the same as those in the up reaches of the Yangtze River basin. Before and after the impoundment of the Three Gorges Reservoir area, there was no sudden change but a decreasing trend in the precipitation during flood season in the upstream Jintao River, Mintuo River, Jialing River, and Wujiang River Basin, and the reservoir area. However, the rainfall during flood season decreased by 7–10 mm ten years− 1 in ups reaches of Mintuo River and the Three Gorges Reservoir area. Our funding might help to support the regulation of water resources responding to drought and flood in the basin.