Many mountainous areas in Campania, southern Italy, are characterized by steep slopes covered by unsaturated volcanic deposits. Shallow landslides are frequently triggered by intense and persistent rainfall events, often turning into debris flows that cause huge damage and casualties. Field hydrological monitoring is a useful tool to develop consistent models of slope response to rainfall, in terms of soil suction and moisture, and to define landslide triggering conditions. This is one of the reasons why since 2002 field monitoring is being carried out in Cervinara, around 50 km northeast of Naples. Since October 2009, rainfall height, soil suction and water content at several locations and depths along the slope are automatically being monitored. The data collected help to demonstrate the effectiveness of such a system for better understanding the hydrological processes occurring in similar slopes of Campania, allowing to distinguish between seasonal suction fluctuations, related to long-term meteorological forcing, and short-term response to rainstorms.

A one-dimensional hydrological model of a slope covered with pyroclastic materials is proposed. The soil cover is constituted by layers of loose volcanic ashes and pumices, with a total thickness between 1.8 m and 2.5 m, lying upon a fractured limestone bedrock. The mean inclination of the slope is around 40°, slightly larger than the friction angle of the ashes. Thus, the equilibrium of the slope, significantly affected by the cohesive contribution exerted by soil suction in unsaturated conditions, may be altered by rainfall infiltration. The model assumes a single homogeneous soil layer occupying the entire depth of the cover, and takes into account seasonally variable canopy interception of precipitation and root water uptake by vegetation, mainly constituted by deciduous chestnut woods with a dense underbrush growing during late spring and summer. The bottom boundary condition links water potential at the soil–bedrock interface with the fluctuations of the water table of the aquifer located in the fractured limestone, which is conceptually modelled as a linear reservoir. Most of the model parameters have been assigned according to literature indications or from experimental data. Soil suction and water content data measured between 1 January 2011 and 20 July 2011 at a monitoring station installed along the slope allowed the remaining parameters to be identified. The calibrated model, which reproduced very closely the data of the calibration set, has been applied to the simulation of the hydrological response of the slope to the hourly precipitation record of 1999, when a large flow-like landslide was triggered close to the monitored location. The simulation results show that the lowest soil suction ever attained occurred just at the time the landslide was triggered, indicating that the model is capable of predicting slope failure conditions.

Forthcoming climate changes, recognized by the international scientific community, are inducing a modification of the hydrological cycles with a direct impact on the piezometric regime of natural slopes and thus on their stability conditions. Particularly regarding active landslides in fine grained soils, the experience based on several well documented cases suggests an evident connection between landslide activity and rainfalls cumulated over some months. As a consequence, the observed change of the rainfall features should provoke variations on the kinematic features of such phenomena. Its role could be not negligible in a landslide risk assessment.Thanks to the availability of a considerable database related to the well documented Orvieto case, regarding precipitations and displacements of an active slide in clay, monitored since 1982, and to a climate projection occurring in the concerned area, provided by a reliable Regional Climate Model, the present paper gives a likely prediction of the long-term scenario of the landslide behavior. According to our results, local climate effects should be responsible of a slow decrease in the displacement rate