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

Mapping soil hydraulic parameters with traditional scaling methods that use laboratory-determined hydraulic characteristics (the 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 (the 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 distribution 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 that 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. Citation Nasta, P., Romano, N., and Chirico, G.B., 2013. Functional evaluation of a simplified scaling method for assessing the spatial variability of soil hydraulic properties at the hillslope scale. Hydrological Sciences Journal, 58 (5), 1059-1071. Resume La spatialisation des parametres hydrauliques du sol avec les methodes traditionnelles de mise a l'echelle qui utilisent des caracteristiques hydrauliques determinees en laboratoire (methode LAB) ne semble pas toujours faisable car elle exige des mesures couteuses, longues et complexes sur des echantillons de sol collectes a divers endroits de la zone d'etude. Une methode alternative de mise a l'echelle (methode AP), a ete recemment proposee pour recuperer indirectement les proprietes hydrauliques du sol en se basant sur la fonction physico-empirique de pedotransfert d'Arya-Paris, qui utilise la distribution granulometrique et les valeurs de densite apparente. Dans cette etude synthetique, nous analysons les performances de la methode AP d'un point de vue fonctionnel, en evaluant, par la methode de Monte Carlo, le biais sur le bilan en eau simule du sol. En depit du fait que la methode AP peut fournir les structures spatiales des proprietes hydrauliques des sols par des procedures experimentales plus rapides et a moindre cout, nous observons un biais important sur la moyenne spatiale du bilan hydrique simule du sol, en raison d'un mauvais calage des parametres de la methode AP et d'une identification imprecise de la structure des correlations spatiales des facteurs d'echelle estimes par la methode AP. Editor D. Koutsoyiannis; Associate editor A. Porporato Citation Nasta, P., Romano, N., and Chirico, G.B., 2013. Functional evaluation of a simplified scaling method for assessing the spatial variability of soil hydraulic properties at the hillslope scale. Hydrological Sciences Journal, 58 (5), 1059-1071.