Exploring the response of shallow groundwater to precipitation in the northern piedmont of the Qinling Mountains, China

Groundwater recharge from precipitation is a complex process that often exhibits strong nonlinearity. This process is influenced by multiple hydrogeological and topographical conditions. This study aims to assess the response of shallow groundwater table to precipitation in the northern piedmont of the Qinling Mountains in China from 2005 to 2015 using a combination of the Mann-Kendall (MK) test, continuous wavelet transform, and cross-wavelet transform. The MK test revealed a slight upward trend of precipitation from 2005 to 2015. In addition, 71% of the shallow groundwater monitoring wells exhibited increasing trends in the groundwater table depth. Continuous wavelet transform demonstrated periodic groundwater responses to precipitation. Both precipitation and groundwater table showed significant monthly oscillation of 9–15 months, while the highest wavelet power was detected at the temporal scale of 12 months. According to the results of the cross wavelet transform, lag times between groundwater level responses and precipitation events were 78, 73, and 99 days for P1-PF1, P2-FT1, and P3-ST1 in pluvial fans, first terraces, and second terraces, respectively. Moreover, the results suggested spatiotemporal variations in the lag time, which might be due to the variation in groundwater levels, aquifer lithology, precipitation intensity, and groundwater exploitation intensity. The current study revealed the spatiotemporal response mechanism of the shallow groundwater to precipitation, providing a scientific basis for assessing the regional water cycle processes and ensuring effective groundwater resource management.