Functional evaluation of a simplified scaling method for assessing the spatial variability of the soil hydraulic properties at hillslope scale.

Mapping soil hydraulic parameters with traditional scaling methods that use laboratory-determined hydraulic characteristics (LAB-method) is not always feasible as it involves expensive, time-consuming and sophisticated measurements on soil samples collected in several locations of the study area. An alternative scaling method (AP-method) has been recently proposed to indirectly retrieve the soil hydraulic properties following the Arya-Paris physico-empirical pedotransfer function, which makes use of particle-size distributions and bulk density values. In this synthetic study we verify the performance of the AP-method from a functional perspective, by evaluating the differences in the simulated soil water budget through a Monte Carlo approach. Notwithstanding the AP-method can provide soil hydraulic property patterns with faster experimental procedures and minor costs, we observe significant bias in the predicted spatially-averaged soil water budget due to a poor parametric calibration of the AP-method and an imprecise identification of the spatial correlation structure of the AP-estimated scaling factors.