Estimating Baseflow Dynamics and Influencing Factors Using WHAT in the Wei River Basin, China

Abstract

Baseflow is critical for sustaining streamflow and managing groundwater resources. The Wei River Basin (WRB) is a semi‐humid region with high water demand that requires robust baseflow analysis, which is essential for stream restoration. Annual baseflow in the WRB was estimated using the Web‐based Hydrograph Analysis Tool (WHAT) in this study, which utilised streamflow data from five gauged watershed stations. Groundwater‐level monitoring data from 2010 to 2015 were also utilised to understand the interaction between baseflow and groundwater levels. The two‐parameter recursive digital filter method within the WHAT programme was employed to estimate baseflow from daily streamflow records. By leveraging this standardised, peer‐validated tool, our analysis maintained consistency in baseflow and direct runoff calculations across all monitoring stations, reducing subjectivity in manual separation methods and enhancing comparability of results. Based on the results, the total annual baseflow measured between 2010 and 2019 ranged from 29574.74 to 910078.73 m 3 /s, while the baseflow index (BFI) varied from 0.56 to 0.67. During the study period, the average BFI was calculated to be 0.63, indicating that baseflow contributed approximately 64% of the long‐term runoff in the examined watersheds. The results also revealed a progressive rise in the BFI along the Wei River, increasing from 0.56 in the upstream sections to 0.67 downstream. Baseflow and BFI spatial patterns indicate groundwater abundance, driven by climate and human factors, with climate more influencing baseflow variability from west to east. Between 2010 and 2019, the basin experienced significant LULC changes. These changes serve as a critical contributing factor modulating decadal baseflow variation, while climate variability remains a dominant driver. Cropland declined, forest and water‐type areas increased, grassland and unused land decreased, and the impervious area expanded. These LULC changes led to a significant increase in annual baseflow despite the climate zone remaining the same.