Time Series Analysis and Temporal Stability of Shallow Soil Moisture in a High-Fill Slope of the Loess Plateau, China

Precipitation-induced soil moisture dynamics are a key factor that plays a critical role in triggering slope failures and geological hazards. This study investigates the response of soil moisture in a high-fill slope to rainfall and explores the influence of the topographic conditions and rainfall characteristics on the soil moisture dynamics. The findings reveal that the topographic conditions significantly influence the soil moisture variability in the high-fill loess slope. The coefficient of variation (CV) follows a decreasing pattern, i.e., slope surface > slope step > flat terrain > slope foot, with the spatial variability diminishing as the depth increases. The response of moisture to rainfall is influenced by the rainfall characteristics. In this study, the peak lag time (PLT), which represents the time interval between the onset of rainfall and the occurrence of the peak cross-correlation coefficient (CCF) between soil moisture and rainfall, is analyzed. The results indicate that, under similar rainfall intensities, the PLT decreases with increasing rainfall amounts. Conversely, for comparable rainfall amounts, a higher rainfall intensity generally shortens the PLT at all positions except the slope step. On the slope scale, the temporal stability of soil moisture exhibits the order flat terrain > slope surface > slope step > slope foot, whereas, in the vertical profile, the temporal stability is positively correlated with the depth. This study provides valuable insights into the hydrological processes of loess high-fill slopes and contributes to understanding slopes' hydrological transformation and evolution.