A rich georeferenced data base on a flood event in the north west of Italy and the knowledge of experts from the different involved disciplines have been used as the basis for the application of an outranking method, ELECTRE III, oriented to the structuring and validation of consistent multicriteria models for hazard evaluation. The models were developed with the aim of explaining the multidimensional nature of slope instability and erosion phenomena in the study area and to help in the definition of a hazard map using criteria which synthesize different interpretations of these phenomena. The integrated use of multicriteria modeling and data analysis, in a GIS analysis context, resulted in a deeper insight into these natural phenomena and could be the proposal of a more ‘flexible’ information system oriented towards decision aiding.