P. Canuti, N. Casagli, F. Catani & A. Iotti (Dipartimento di Scienze della Terra, Universita` di Firenze, via La Pira 4, 50121 Firenze, Italy)

This note describes some techniques for evaluating the landslide impact on developed areas and the countermeasures adopted for risk prevention and emergency management. The presented methods are based on the guidelines recently proposed by the National Group for Hydrogeological Disaster Prevention (GNDCI) for the preparation of "Plans of Landslide Forecast and Prevention". Examples are drawn on some emergency events occurred between 1992 and 1996 in the Tuscany and Emilia-Romagna regions. The complete risk assessment requires the separate evaluation of landslide hazard and of the potential worth of losses. The application of GIS techniques for the first case is well known in the scientific literature. This note describes in particular some examples of application of GIS for the forecast of the possible consequences of mass movements, in course of event, taking in special account cases of induced risk, as those which occur from the interaction of slope movements with river channels. The use of GIS allows us to define different scenarios of evolution of the danger and to associate to each one a cost in term of loss of properties and human lives at risk. Each scenery is defined on the basis of some indicators measurable with field surveys or with monitoring systems. The different scenarios can be analysed in probabilistic terms with reference to a probability tree. From the assessment of conditional probabilities, based on experience and on a series of similar events, it is possible to assess the probability of occurrence of each risk scenery. Knowing the economic value associated to the different elements at risk it is possible to assess completely the total risk. For each scenery the activity of first intervention can be scheduled, aimed to the reduction of the vulnerability of the elements at risk and to the consequent mitigation of damages.