Messina area (Italy) range stretches along the coast and have high relief energy. Huge rainfall events cause rapid gravitational phenomena classified as debris flows. The rampant urbanization developed in the last decades in the Messina Municipality has determined a fragile territorial settlement, prone to be heavily damaged by debris flows, as in October 2009. In order to support the community in tackling the risk conditions which it is subjected to, it is necessary to develop “non-structural” measures, characterized by a high level of environmental sustainability. The scientific community and the public authorities responsible for land management and involved in the mitigation of the geomorphological risk are paying a specialattention to the development of monitoring and alarm systems able to improve the current civil defence plans. Based on the historical information on rainfall, this study deals with the triggering thresholds of debris flows. The results provide additional elements to the knowledge of the critical rainfall, useful for developing effective early warning systems. . © Springer International Publishing Switzerland 2015.