Effect of a Heavy Rainstorm on the Surface Hydrodynamic Properties of a Sandy-Loam Soil

Changes in surface-soil hydrodynamic properties associated with torrential natural rainstorms are largely unknown. This investigation aimed at verifying if the surface hydrodynamic properties of a sandy-loam soil varied due to the heavy rainfall event (130 mm in nearly three hours) that occurred in the summer of 2020 at Palermo (Italy) and also to establish if soil recovery processes occurred soon after the event. The soil of an orchard was sampled immediately before the rainstorm and a few days and 1.5 months later. The rainstorm determined a moderate decrease (by 1.8 times) of the saturated soil hydraulic conductivity, Ks, and an increase of its relative variability. In the subsequent weeks, the lowest Ks values detected soon after rainfall tended to disappear but the soil remained moderately less conductive (by 1.4 times) than before rainfall. Wetting and subsequent drying did not influence the means of macroscopic capillary length, λc, characteristic microscopic pore radius, λm, and depth of the wetting front, dwf, but reduced relative variability of these parameters. Therefore, this investigation confirmed that Ks is a sentinel soil property. It also suggested that a torrential rainstorm can have no more than a moderate impact on the surface-soil hydrodynamic properties. Additional investigations are necessary to (1) verify if the canopy should have a key role on the stability of the soil properties in meteorologically critical conditions; (2) determine if a link between natural and soil-perturbing artificial events can be established to investigate the short-term dynamics of the surface soil properties more easily; and (3) test the hypothesis that the greater the disturbance the faster the onset of reorganization processes.