Spatial Contrasts in Hillslope Soil Water Redistribution Under Varying Rainfall and Antecedent Moisture Conditions

Hillslope soil water redistribution controls transient storage, vertical drainage, and the persistence of elevated soil moisture after rainfall, but field interpretation remains difficult where direct flux measurements are unavailable. This study combined 15 min rainfall observations, soil moisture measurements at six depths from 0.10 to 0.60 m across upslope, midslope, and downslope positions, soil water retention measurements, and two-dimensional Richards equation modeling to characterize redistribution along a mountain hillslope transect in the Ganwuli Watershed, southwestern China. Retention measurements revealed local hydraulic heterogeneity, while model performance varied across depths and slope positions. Controlled scenarios produced different spatial patterns of modeled moisture increments under rainfall scaling and changes in initial moisture, including a larger midslope increment under a dry initial state with unchanged rainfall. Under the baseline event, the upslope and midslope mean increments were close, at 0.0265 and 0.0293 m3·m−3, respectively, yet the upslope mean profile met the recovery criterion while the midslope profile did not within the analysis period. These conditional findings support monitoring initial moisture, event wetting, and recession together as well as retaining observed initial moisture differences when applying models to this shallow hillslope.