Study on the response mechanism of groundwater to rainfall in different geomorphic units of semi-arid regions

This study was conducted at the Agula Eco-hydrological Experimental Station, located in the southeastern part of the Horqin Sandy Land, Tongliao City, Inner Mongolia, North China (43°18’48’’-43°21’2’’N, 122°32’30’’-122°41’00’’E) This study investigates groundwater level responses to precipitation across geomorphic units (mobile dunes, fixed dunes, semi-fixed dunes, meadows) in Horqin Sandy Land from 2016 to 2023. Five time-series analysis methods (STL decomposition, wavelet analysis, cross-correlation, etc.) were applied to characterize groundwater dynamics in phreatic and weakly confined aquifers, including seasonal variability, decorrelation times, and rainfall lag effects. Results demonstrate that the groundwater levels in phreatic aquifers rose by 0.64–0.97 m in dunes but remained stable/declined in meadows; weakly confined aquifers showed contrasting trends (0.33–1.08 m rise). Seasonal fluctuations peaked at 1 m in meadow phreatic aquifers and 0.55 m in meadow weakly confined aquifers, with 1–2 month lags in weakly confined systems. Decorrelation times ranged 21–40 days in phreatic aquifers and 16–29 days in weakly confined aquifers, indicating strong memory effects. Rainfall response lags varied from 1 day (meadows) to 113.5 days (fixed dunes in weakly confined aquifers), governed by soil permeability and groundwater depth. These findings provide a scientific basis for groundwater management and ecosystem restoration in desertified regions. • Aquifer water level driven mainly by geomorphic units and aquifer types. • Quaternary aquifers show significant memory effects, primarily driven by groundwater depth. • Groundwater rainfall response lag time mainly driven by groundwater depth and soil permeability.