Time-lag effects and periodic responses in precipitation-shallow groundwater system of Qiaocheng District, China: a combined diagnosis using wavelet and long-series statistical analysis

ABSTRACT Groundwater systems demonstrate non-linear responses to precipitation, necessitating multiscale investigations to reveal recharge dynamics. This study aims to examine how shallow groundwater levels respond to precipitation changes. Focusing on the Qiaocheng District in East China, the study uses data from 2000 to 2022 to investigate the temporal and spatial variation characteristics of groundwater levels on monthly and annual scales, and statistically analyzes the changes in response thresholds of groundwater level to precipitation with different thicknesses of the unsaturated zone. Wavelet analysis is employed to quantify the response lag times of groundwater levels to low-frequency and high-frequency precipitation signals. Specifically, for low-frequency precipitation (with a 365-day period), the lag time increased from 2–3 months in the 2000s to 6–7 months in the 2010s. For high-frequency precipitation (with a 32-day period), the lag time from 2020 to 2022 was approximately 4–13 days. By distinguishing between various frequencies, this study investigates the dynamic processes of groundwater level responses to periodic changes in precipitation, aiding regional groundwater recharge assessment.