Abstract: The runoff and sediment situation in the watershed has changed with climate change and the intensification of human activities. Quantitative analysis of the runoff and sediment effects of precipitation variation and human activities is a hot topic in current water science research. Based on the hydrological and meteorological observation data of Zhangshui watershed in the upper reaches of Ganjiang River from 1961 to 2020, we quantitatively analyzed the contribution rate of precipitation variation and human activities to the changes of runoff and sediment, and the critical value of the runoff and sediment effect of human activities to the annual precipitation response by using the slope change ratio of accumulative quantity and empirical statistical analysis. The results showed that precipitation and runoff showed a nonsignificant downward trend (P>0.05), and the sediment transport showed a significant downward trend (P<0.001). The abrupt change of precipitation and runoff was in 2003, and the abrupt change of sediment was in 1998. The contribution rates of precipitation variation and human activities to runoff reduction were 10.7% and 89.3%, and to sediment reduction were 3.5% and 96.5%, respectively. The critical values of runoff and sediment reduction effects of human activities in response to annual precipitation were 1170 mm and 858 mm, respectively. Our results could provide scientific basis for watershed ecological construction and optimal management of water and land resources.

Key words: Zhangshui watershed, precipitation variation, human activity, runoff and sediment change, critical value