Baseflow variations and its causes in a subtropical watershed of southern China

Baseflow is an essential component of streamflow and plays a crucial role in maintaining the stability of streamflow. However, few quantitative studies have identified the effects of leading factors on baseflow variation at the small watershed scale, especially in subtropical China. In this study, the small watershed(Pengchongjian watershed, 2.90 km2), located in Southern China, was considered to explore the quantitative impact of precipitation, evapotranspiration, temperature, and vegetation restoration on baseflow. The digital filter method was used to separate baseflow by daily streamflow records from 1983 to 2014. The stepwise regression models were developed for selecting significant influencing factors of baseflow at seasonal and annual scales. The direct and indirect effects, as well as their quantitative relationships between baseflow and multiple factors, were clarified by the path analysis. The results showed that filtered average annual baseflow significantly decreased(p < 0.05), ranging from 72.82 to 305.85 mm, and the average yearly baseflow index was 0.22. In addition, various significant influencing factors of baseflow had different direct and indirect effects on baseflow at seasonal and annual scales. The precipitation was the dominant factor with respect to the direct impact, which directs path coefficient was 0.891 in spring, 0.823 in summer, 1.599 in autumn, 1.332 in winter, and 0.917 in an annual scale, respectively. In terms of the indirect effects, evapotranspiration played a leading role during the spring, autumn, winter, and annual scale, whereas the average temperature was the dominant factor during the summer. Overall, results demonstrated that the baseflow variation was mainly attributed to climate change. The present works are beneficial for revealing the internal mechanism of the baseflow variations in the study area, and it can provide a scientific basis for managing water resources in the watershed.