 The paper uses a simulation approach to quantify and compare the contributions of climate variability, human activities, land use change and reservoirs operations, and their combined effects on stream flow changes in 272 sub-basins of the Yangtze River basin over five different periods. Results show that climate variability played a leading role in annual scale outflow changes, while reservoir operations had the greatest impact on seasonal variations in discharge at that on station during specific periods. The study supports decision-making in regional water resources planning and management. This article was offered by Ming Nye, Wang Zhang Ming Nye, Wang Zhang, Minit Liu, and others.