MULTIVARIATE ANALYSIS OF GULLY-EROSION PROCESS: SUSCEPTIBILITY ASSESSMENT AND TEMPORAL VALIDATION IN A WATERSHED OF NORTH-CENTRAL SICILY, ITALY

In the last decades a number of studies have been carried out aiming to model soil erosion processes and describe their spatial variability, in terms of rates of soil loss and future location of erosion features. In contrast to the effort to investigate rill and interrill soil erosion process, relatively few studies have focused on quantifying and predicting gully-erosion role (Martinez-Casasnovas, 2003), even if this phenomenon significantly contributes to soil loss in the Mediterranean region (Poesen et al., 1998; Vandekerckhove et al., 2000). Studies focusing on gully-erosion processes can be distinguished according to their main goals and methods: evaluation of soil loss volumes by repeated morphometric analysis of gullies (Vandaele and Poesen, 1995; Martinez-Casanovas, 2003; Casali et al., 2006); assessment of threshold values of topographic attributes for the initiation, distribution and location of gullies (Moore et al., 1988; Montgomery and Dietrich, 1992, Desmet et al. 1999; Samani et al., 2009); development of gully-erosion models to predict and simulate spatial and temporal variability of this process (Souchere et al., 2003; Sidorchuk et al. 2003; Bou Kheir et al. 2008; Conoscenti et al., 2008). The research here presented, which can be included in the last category, follows a multivariate approach to define spatial relationships between a set of conditioning factors and the occurrence of gullies; these relations are exploited to generate a gully-erosion susceptibility map of a watershed located in a north-central sector of Sicily.