Changes in Streamflow Pattern and Complexity in the Whole Yangtze River Basin

The assessment of streamflow patterns and their complexity variations across multiple timescales within river basins is a crucial aspect of water resource management and policy formulation. In this study, the Hurst coefficient, Mann-Kendall nonparametric test method, streamflow pattern indices, and sample entropy (SampEn) analyses were used to investigate the streamflow pattern in the whole Yangtze River basin at annual, monthly, and daily scales. The results show that with the increase in the time resolution, the streamflow shows more complex changing characteristics and streamflow changes more obviously on the monthly timescale than on the annual one. The annual mean streamflow decreases only in some of the tributaries, while the monthly streamflow shows significant increasing trends in the dry season and significant decreasing trends in the late wet season in almost the whole basin. Results also show that the minimum extreme streamflow indices increase in almost the whole basin. The maximum indices show decreasing trends in most of the tributaries and the Yichang gauge in the main reach. The streamflow complexity in the tributaries is higher and the complexity increases from upstream to downstream along the main reach in the basin. Along the main reach, the average SampEn increases downstream of the reach with values of 0.05, 0.07, 0.10, 0.12, 0.14, and 0.14 at Shigu, Pingshan, Cuntan, Yichang, Hankou, and Datong, respectively. These findings are helpful for understanding the hydrological characteristics and water resource management in the Yangtze River basin.