Impact of soil and water conservation measures and precipitation on streamflow in the middle and lower reaches of the Hulu River Basin, China

Precipitation variation and soil and water conservation (SWC) measures mostly determine the dynamics of streamflow in the Hulu River Basin. In particular, SWC measures play an essential role in controlling streamflow reduction and soil loss in the Hulu River Basin. The objective of this study is to quantitatively explore the effect of SWC measures and precipitation on streamflow changes in the middle and lower reaches of the Hulu River Basin. In this study, a long-term measured annual streamflow data from two major hydrological stations was used to analyze variations in streamflow in this basin. The Mann-Kendall trend test and the change-point analysis method were applied to analyze the trend of streamflow datasets. The results indicated that the annual streamflow in the middle and lower basin of the Hulu River (1975-2016) had a similar decreasing trend to streamflow change of the entire basin (1960-2016), with the abrupt change point of annual streamflow occurred in the year 1986. In addition, the streamflow exhibited a slightly increasing trend due to the more precipitation increase in the basin throughout 1999-2016. From 1999 to 2016, the impact of precipitation and SWC measures on streamflow is quantitatively assessed by using a multiple linear regression model. The result showed that SWC measures could effectively delay and reduce streamflow. The analysis of the regression coefficients suggested that SWC measures had a positive ecological effect on streamflow decrease, whereas precipitation had a significantly positive effect on streamflow increase. The precipitation had a higher contribution to streamflow changes than SWC measures. For the change of annual streamflow, precipitation contributed 79.6%, the Grain-for-Green program and check dams contributed 13.4% and 7%, respectively. A comparison of the impact of SWC measures on streamflow showed that the Grain-for-Green program measure had a more significant impact on streamflow reduction in the middle and lower reaches of the Hulu River Basin. In conclusion, these results can guide future water resource planning and management, and the allocation of SWC measures in the entire Hulu River Basin.