An optimized baseflow separation method for assessment of seasonal and spatial variability of baseflow and the driving factors

Baseflow is an important component of river or streamflow.It plays a vital role in water utilization and management.An improved Eckhardt recursive digital filter(IERDF)is proposed in this study.The key filter parameter and maximum baseflow index(BFImax)were estimated using the minimum smoothing method to improve baseflow estimation accuracy.The generally considered BFImax of 0.80,0.50 and 0.25 according to the drainage basin’s predominant geological characteristics often leads to significant errors in the regions that have complex subsurface and hydrologic conditions.The IERDF improved baseflow estimation accuracy by avoiding arbitrary parameter values.The proposed method was applied for baseflow separation in the upstream of Yitong River,a tributary of the Second Songhua River,and its performance was evaluated by comparing the results obtained using isotope-tracer data.The performance of IERDF was also compared with nine baseflow separation techniques belonging to filter,BFI and HYSEP methods.The IERDF was also applied for baseflow separation and calculation of rainfall infiltration recharge coefficient at different locations along the Second Songhua River’s mainstream for the period 2000–2016.The results showed that the minimum smoothing method significantly improved BFImax estimation accuracy.The baseflow process line obtained using IEDRF method was consistent with that obtained using isotope 18 O.The IERDF estimated baseflow also showed stability and reliability when applied in the mainstream of the Second Songhua River.The BFI alone in the river showed an increase from the upstream to the downstream.The proportion of baseflow to total flow showed a decrease with time.The intra-annual variability of BFI was different at different locations of the river due to varying climatic conditions and subsurface characteristics.The highest BFI was observed at the middle reaches of the river in summer due to a water surplus from power generation.The research provided valuable information on baseflow characteristics and runoff mode determination,which can be used for water resources assessment and optimization of economic activity distribution in the region.

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.