Abstract
Baseflow is a critical component of streamflow in arid areas. Determining variations in baseflow and the factors affecting it have positive roles for water resource utilization in arid watersheds. Two watersheds, the Hailiutu River watershed (HLTR) and the Dali River watershed (DLR), located in two different geomorphological regions of the middle Yellow River, were selected for this study. By using the Eckhardt segment method (fourth digital filtering method, DF4), baseflow was separated from streamflow based on its daily data. Mann-Kendall trend test analysis (M-K trend test) was used to test the trends in baseflow change at different times. Complex Morlet wavelet analysis was used to judge baseflow periodicity. Heuristic segmentation and sequential cluster analysis were used to identify the potential change points in the baseflow series for the two regions together with Pearson correlation coefficient. The results showed: (1) the annual baseflow of the HLTR and the DLR showed significantly decreasing trends (P < 0.01), more significantly for the HLTR (0.33 × 108 m3) than the DLR (0.20 × 108 m3). The annual base flow index (BFI, baseflow/total streamflow) in the wind-sand region (0.75) was larger than for the loess region (0.55), and the BFI in the wind-sand region was more stable in different periods. (2) The annual baseflow of the HLTR and the DLR both exhibited a complete main cycle of 42 years and 38 years, respectively. The change points of the annual baseflow in the HLTR were 1967 and 1986, and 1971 and 1996 in the DLR. (3) There was no significant change in annual precipitation in the two watersheds, while annual reference evapotranspiration (ET0) in the DLR showed a significant increasing trend (P < 0.01). The normalized difference vegetation index (NDVI) on the DLR (0.40) was higher than on the HLTR (0.26). (4) Baseflow in the wind-sand region, where vegetation improvement was the only ecological activity, decreased faster than in the loess region where there had been numerous ecological measures such as vegetation improvement, check dams and terraces. This implied that comprehensive measures such as these were helpful in slowing the rate at which the baseflow decreases. Therefore, the effect of ecological construction should be considered in future baseflow studies in other geomorphological types within the Middle Yellow River Basin.
Highlights
Baseflow is an important component of streamflow in arid and semi-arid areas, and plays a crucial role in maintaining production and domestic water supply and the health of the watershed ecosystem [1]
The effect of ecological construction should be considered in future baseflow studies in other geomorphological types within the Middle Yellow River Basin
Using Pearson correlation and stepwise multiple regression, Sandhi et al analyzed the relationships between topography, precipitation, potential evapotranspiration, sediment concentration and baseflow, and showed that topography, sediment concentration and BFI were closely related, whereas topography, precipitation and baseflow were not significantly related [8]
Summary
Baseflow is an important component of streamflow in arid and semi-arid areas, and plays a crucial role in maintaining production and domestic water supply and the health of the watershed ecosystem [1]. Mwakalila et al calculated the BFI for a semi-arid area in Tanzania, and used regression analysis to reveal the influence of watershed features on the baseflow. He believed that the correlations between BFI, climate and geological conditions in the watershed were significant, being characterized by high precipitation and low evapotranspiration, and a rich granite or basalt underlying surface. Arnell considered that the two most basic meteorological factors, precipitation and temperature, have direct impacts on the baseflow of a watershed [9], but Schaake and Liu tended to believe that streamflow in low-flow periods was more affected by climate change than in flood periods [10]. Arnell analyzed the frequency of extreme floods in Europe, and found that droughts and elevated temperatures were not a direct cause of decreased baseflow [12]
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