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Global climate change and intensifying human activities have dramatically changed the runoff of Dongting Lake. This study investigated the runoff variations and associated impacts of climate change and human activity for the four inflow sub-basins of Dongting Lake. Multiple linear regression method and double-mass curve method were used to quantify the effects of climate change and human activities on water discharge. Results showed that the streamflow of the Xiangjiang, Zishui and Yuanjiang rivers exhibited an abrupt change in 2003, 2003 and 2005, respectively, whereas no significant turning year was detected for Lishui River. The impacts of climate factors and human activities were consistent using the two methods. The contribution rate of climate change to runoff reduction in Xiangjiang River was about 85-92% and the impact of human activities ranged from 8 to 15%. For the runoff changes in the Zishui and Yuanjiang River basins, results showed that the impact of climate factors ranged from 63 to 88% and from 62 to 82%, respectively. In comparison, the anthropogenic impact ranged from 12 to 37% and from 18 to 38%, respectively. This study will provide important insights into water resource management and planning for Dongting Lake basins.