Variations and controls on groundwater recharge estimated by combining the water-table fluctuation method and Darcy’s law in a loess tableland in China

Understanding the mechanisms of groundwater recharge and their control factors will benefit water resources protection, in particular, for the regions with thick vadose zones. The water-table fluctuation method is popular for recharge estimation; however, the lateral flow has rarely been excluded. This study investigated recharge mechanisms in the Changwu Loess Plateau using data from five monitoring wells from 1976 to 2017, by combining the water-table fluctuation method and Darcy’s law for recharge estimation. Spatially, the annual average recharge (lateral flow excluded) was 13 ± 4 mm, equivalent to 2% of mean annual precipitation, and decreased from the center to the edge of the tableland. Temporally, the recharge decreased by 3 ± 1 mm year −1 over the study period. The results of cross-correlation and wavelet coherence analysis showed that there was a time lag of 1–8 months between recharge and rainfall. This study further found that relative contributions of climate, vegetation, lateral flow, and anthropogenic impact (population and land-use change) to recharge reduction were 22, 11, 17, and 50%, respectively, implying that human activities are the dominant factors controlling recharge rate in the tableland. This study provides technical investigations and implications for water resource conservation in similar regions.