Objective The aims were to investigate the monthly-scale dynamics and spatial distribution of soil water in a forested slope in the Longmen Mountain.

Method An in-situ electrical resistivity tomography (ERT) monitoring system with two 14.5 m survey lines was deployed on an evergreen broad-leaved forest slope in Pingwu, Sichuan, within the Longmen Mountain. A power function fitting method was used to establish a resistivity-to-soil water content conversion model. This model reconstructed the monthly-scale dynamic distribution of slope soil water from February to November 2024.

Results The power function-based model relating inverted soil resistivity to volumetric water content was statistically significant (P < 0.001), with R² > 0.8. Model-estimated water content showed a highly significant correlation with TDR-measured values (R² = 0.655, P < 0.001; RMSE = 0.0393 cm³ cm⁻³), validating the model’s reliability. Temporally, the root zone soil (5 ~ 85 cm depth) exhibited distinct wet-dry cycles: water content increased from February to April; displayed a "decline–rise–decline–rise" fluctuation pattern between May and August influenced by rainfall, and gradually increased from September to November as vegetation transpiration weakened. Spatially, soil water contents differed significantly between slope positions, with the upper slope position being significantly higher than the lower position (P < 0.05).

Conclusion As a novel soil water monitoring technique, ERT demonstrated reliability and effectiveness in quantitatively inverting the monthly-scale spatiotemporal dynamics of soil water on the Longmen Mountain slope. This study provides a scientific basis for analyzing hillslope hydrological processes and enhancing water conservation functions in the forest ecosystems of the study area.