Effects of the competing controlling factors of rainfall, landscape position and soil depth on moisture responses in the Mollisol region of China

Extreme rainfall is occurring more frequently, and its impacts on erosion can be effectively mitigated through soil horizons, which enhance infiltration and reduce surface runoff. However, the interactive effects of rainfall and landscapes on soil moisture responses remain unclear. The objective of this study was to quantify the interactive influence of rainfall patterns and landscape positions (upslope [US], midslope [MS], and downslope [DS]) on event-scale moisture response metrics across various soil depths. Results indicated that the moisture response magnitude (Δs, m3 m−3) generally decreased with increasing soil depth and decreasing slope position, while exhibiting a positive correlation with rainfall amount. The response percentage peaked during heavy rainfall within shallow layers (0–20 cm), whereas it remained limited to around 14% under light and moderate events. Moreover, the simultaneous moisture peak across soil layers, or earlier peaks in deeper layers during heavy rainfall events, was observed at all positions. For slope with lower initial moisture (S1), the response metrics at US and MS were slightly greater than those of Slope 2 (S2). However, no significant differences were observed at the DS position between S1 and S2, indicating that the influence of the slope length cannot be ignored. Overall, MS and DS positions were critical for explaining response variance, while rainfall type was the key factor for moisture dynamics across all depths. These findings suggest that the response timing and regimes of peak moisture in diverse soil layers should be considered to effectively manage erosion risks.