Temporal variability of soil water content in a semiarid hillslope across time scales: Effect of soil surface condition

Soil water content (SWC) is a key factor affecting spatio-temporal dynamics of vegetation structure and resilience. In semi-arid environments, seal formation at the surface of bare soils is a widespread phenomenon that significantly affects flow processes and consequently, the SWC regime. However, very little knowledge currently exists regarding the way surface sealing modulates SWC temporal variability during different rainfall regimes and time scales. This study uses a physically based and spatially explicit model at the hillslope scale to quantify the effect of soil surface sealing on temporal variability of SWC for a variety of rainfall events and different time scales. Specifically, we focus on the relation between the mean SWC at its temporal variability at different hillslope locations, and the factors affecting it. Surface sealing was found to significantly affect SWC temporal variability at all studied time scales. The relation between SWC mean value and its temporal variability was found to be negative at the rainfall event timescale, and to shift to positive at the seasonal and decadal timescales. At the rainfall event scale, in both sealed and unsealed systems, maximal temporal variability could be found at the upper interfluvial areas of the hillslope. On longer time scales, hillslope locations with maximal temporal variability depend on the characterization of the soil surface, i.e., sealed or unsealed. Considering water to be a limiting factor in dry environments, persistent higher SWC values and lower temporal variability in the presence of a seal layer might favor local vegetation establishment.