Soil hydrological response is crucial for controlling water flow and biogeochemical processes on hillslopes. Understanding soil water dynamics in response to rainfall is essential for accurate hydrological modeling but remains challenging in humid mountainous regions characterized by high antecedent moisture and substantial heterogeneity. We sought to elucidate soil water response patterns to rainfall by estimating lag time, wetting front velocity, rainfall threshold, and preferential flow (PF) frequency in 166 rainfall events across 36 sites on two hillslopes within the Hailuogou catchment, located on the eastern Qinghai–Tibet Plateau. Results indicated that over 90% of the events triggered rapid soil water potential (SWP) responses to depths of 100 cm, with faster responses observed at steeper upslope positions with thinner O horizons. Even light rainfall (2–3 mm) was sufficient to trigger SWP responses. PF was prevalent across the hillslopes, with higher occurrence frequencies at upslope and downslope positions due to steep terrain and consistently moist conditions, respectively. Using the Multivariate Adaptive Regression Splines (MARS) model, we found that site factors (e.g., soil properties and topography) had a greater influence on SWP responses than rainfall characteristics or antecedent soil wetness conditions. These findings highlighted the value of SWP in capturing soil water dynamics and enhancing the understanding and modeling of complex hillslope hydrological processes.
Read full abstract