Abstract: In the recent decades, the hydrological regimes of Poyang Lake clearly changed, the persistent dryness and rapid shrinkage of the Poyang Lake seriously threatened the security of the local human life and the stability of wetland ecosystem. Poyang Lake suffers from frequent droughts and floods in the Yangtze River basin, which greatly altered the river, lake, and wetland hydrological processes accompanied by the degeneration of the ecosystem, also affects the local industrial and agricultural production as well as the regional social and economic development. This paper analyzes the evolution of hydrological regimes in the Poyang Lake region and associated casual influencing factors. We focus on the integrated lake-catchment-Yangtze River system. The data of the 62-year lake water levels, the runoff of the Yangtze River and catchment discharges were used to explore the hydrological evolution under the changing environment. Additionally, the Mann-Kendall testing and Sen’s slope methods were adopted in this study. Statistical results show that the Mann-Kendall testing and Sen’s slope methods have similar results in terms of the trend analysis, while lake water level, the catchment river inflow and the Yangtze River discharge exhibit different variation trends in the flood and dry seasons. In addition, the extreme regimes for the droughts and floods are affected by the five major rivers and the stem stream of the Yangtze River. Generally, the characteristic values of lake water level (except for the Kangshan station), catchment discharge (except for the Lijiadu station), and the Yangtze River discharge (except for Yichang station) have the same decreasing trends before the 1970s, while they exhibit distinctly fluctuation between the 1970s and 1980s; however, the characteristic values have obviously increasing trends during the period from 1990 to 2000. A significantly decreasing variation trend is also observed after 2005. The finding in this paper would be helpful to the regulation and management of floods and droughts, and would provide scientific support and reference for the ecological wetland protection in Poyang Lake. Nevertheless, either the runoff changes of the five rivers basin or those of the Yangtze River are subject to the superposition of the climate change and human activities interfere to varying degrees.

Key words: water level of the Poyang Lake, five major rivers, the Yangtze River, Mann-Kendall testing, Sen’s slope