The assessment of baseflow separation method and baseflow characteristics in the Yiluo River basin, China

Baseflow is a major component of streamflow during the dry season and has a crucial role in maintaining the stability of river flows in many regions. To investigate the suitability of baseflow separation methods and baseflow characteristics in the Yiluo River basin, seven baseflow separation methods, including the digital filtering method, HYSEP method and UKIH method, were selected to separate the measured daily streamflow data from five stations within the basin. The baseflow separation results were evaluated with reference to a typical recession curve in the Yiluo River to select the most appropriate separation method for the basin. The results show that the Chapman digital filter (F2) method, with an NSE value closest to 1 and the smallest RMSE value, is the most stable and reliable baseflow separation method for use in the basin. The simulated baseflow process line can reflect the receding process and hysteresis effect of runoff. The intra-annual trend of baseflow is the same as the streamflow, with a single-peaked distribution, while it is opposite to the baseflow index (BFI). According to the Seasonal Kendall test, the annual baseflow at the Changshui (II) station showed a highly significant reducing trend during the period from 2000 to 2019. The Longmenzhen and Baimasi stations showed a significant increasing trend in spring. In general, there is no trend in the BFI on a seasonal basis. The study can provide theoretical support for runoff and groundwater management in the basin.