Investigating Properties and Attribution of Streamflow Nonstationary Change on the Loess Plateau of China: Distinguishing the “Greening” Effects

The ecological restoration efforts on the Chinese Loess Plateau (CLP) have garnered considerable interest from experts and scholars worldwide, primarily because of their substantial impact on watershed runoff production. Therefore, it is of utmost importance to accurately assess the effects of greening in order to ensure the attainment of regional water security and sustainable basin development in the CLP region. The selected research area for this study is the Beiluo River basin, which is a representative watershed on the CLP situated in the center area of the Yellow River. To assess the impact of greening programs on the CLP, the quantitative attribution approach and change point testing method were utilized to study the nonstationary alterations in runoff over the period from 1959 to 2016. The findings of the study indicate that abrupt shifts in runoff patterns in the Beiluo River watershed occurred in the years 1979 and 1994, dividing the whole period into three periods. The time spanning from 1959 to 1978 is largely acknowledged as a significant climatic epoch that has been primarily influenced by the phenomenon of climate change. In contrast, the time between 1980 and 1993 is predominantly distinguished by the significant impact of direct human activities (DHA). Moreover, the observed variations in streamflow between the years 1995 and 2016 can be attributable to the combined influence of alterations in vegetative cover (AVC) and DHA. During the entirety of the examination period, precipitation emerged as the predominant factor contributing to climate change, only leading to a decrease in streamflow by a magnitude of 2.2 × 108 m3. Additional elements that played a role in this phenomenon were AVC and DHA, also known as indirect and direct human impacts. Between the years 1980 and 1993, it was observed that DHA contributed to approximately 20% of the total human-induced decrease in streamflow. Furthermore, it has been demonstrated that the DHA and AVC during 1995–2016 have played a significant role in accounting for 30% and 50% of the total reduction in streamflow, respectively. Hence, it can be inferred that the implementation of greening CLP has emerged as the primary determinant contributing to the decline in runoff levels within the Beiluo River basin in recent times. Consequently, this issue warrants heightened scrutiny due to its potential to jeopardize both water resource sustainability and societal progress within the CLP.