Luca Comegna

Potential effects of incoming climate changes on the behaviour of slow active landslides in clay

Today, a stimulating debate involves the scientific community about the impact of presumable future climate changes on the human life. One of the main question marks concerns their effects on hydrological hazards. Unfortunately, often such a debate is not based on reliable data. The paper proposes a methodology based on the coupling of climatic scenarios and geotechnical analyses accounting for the potential changes in climate parameters. Some analyses have been carried out to forecast the future behaviour of a slow landslide in clay. According to the adopted model, local climate effects should cause a slow decrease in the displacement rate.

Validation of a Simulation Chain to Assess Climate Change Impact on Precipitation Induced Landslides

Since prehistoric times, the clayey slopes of Orvieto (Central Italy) have been affected by slow movements directly related to soil–atmosphere interaction. Understanding how climate changes could affect future evolutions of such movements is a challenging issue; to this aim, a simulation chain is set up: General Circulation model (GCM) outputs are dynamically downscaled through regional climate models (RCMs); rainfall values are then subjected to techniques to correct biases; so obtained rainfall time series can be adopted as input for tools evaluating slope stability conditions. Three bias correction techniques (BCT) have been applied: linear-scaling, quantile mapping and Analogs method. This work analyses their strength and limitations as well as their capability for outperforming the uncalibrated RCM outputs under current climate conditions (1981–2010) for the Orvieto case study. These results suggest that the BCT may be very useful tools for climate change impact studies where users require high resolution data and systematic errors to be minimized.

Potential effects of climate changes on soil–atmosphere interaction and landslide hazard

In the recent years, the scientific community is involved in an intense debate around the effects of global warming. In fact, this could determine valuable changes in atmospheric forcing that govern the soil–atmosphere interaction and, in turn, water budget in the subsoil, with unpredictable consequences, inter alia, on geohydrological hazards. An early and proper assessment of the magnitude of such phenomena would be of great importance in establishing the priorities and timing in adaptation strategies. The paper reports some results obtained through a simulation chain which accounts for the potential climatic changes induced by two different socioeconomic concentration scenarios in atmospheric forcing and consequent changes in soil moisture and, then, slope response. The analyses concern a site located in Southern Italy, representative of Mediterranean area, deemed an “hot spot” for future climate changes. It is shown that, beyond the variations induced by climate changes, soil nature and land cover could play a major role.

Investigation on the Hydraulic Parameters Affecting Shallow Landslide Triggering in a Pyroclastic Slope

Large mountainous areas surrounding the city of Naples (southern Italy) are characterized by the presence of steep slopes covered with few meters of loose pyroclastic materials in unsaturated conditions, lying upon a fractured limestone bedrock, the stability of which is ensured by the contribution to shear strength due to suction. Wetting of the soil cover during rainfall infiltration may cause the triggering of shallow landslides, sometimes developing in form of fast and destructive flows. In this preliminary study, a sensitivity analysis is carried out, aiming at quantifying the effects on the hydrological response of a slope to precipitations, of some factors, related either to the hydraulic properties of the soil cover or to the permeability of the soil-bedrock interface. In particular, the sensitivity analysis refers to the slope of Cervinara, around 40 km northeast of Naples (Italy), covered by a pyroclastic deposit with an average thickness around 2.0 m, and characterized by an average slope angle of 40°. For the sake of simplicity, the analysis is carried out by means of a one-dimensional infiltration model, based on the Richards’ equation written for a single homogeneous soil layer. The obtained results highlight that the equilibrium of the slope during rainfall infiltration is affected not only by the hydraulic characteristics of the soil cover, but a major role is played by the permeability of the soil-bedrock interface.

The Impact of Climatic Changes on the Behaviour of Active Landslides in Clay

Forecasting the effects of forthcoming climate changes on natural hazards is a new frontier of the research. The problem is crucial for landslide hazard but available data are still doubtful, thus only some hypotheses can be drawn. The paper examines the potential effects of climate during next 50 years on two active landslides in clay. Considerations are based on data regarding local rainfall history, available climatic scenarios, monitoring and results of simple geotechnical analyses.

Potential Effects of Climate Changes on Landslide Activity in Different Geomorphological Contexts

The anthropogenic global warming could significantly affect weather patterns, with variable impacts at the regional scale. Geo-hydrological hazards represent an interesting example of the possible impacts. We present a study of the effects of potential climate change on slope stability conditions in two different contexts in the Italian Apennines. Although the two examined sites are 400 km apart, climate simulations return similar variations in weather patterns, which are characterized by a strong increase in air temperature, a reduction in seasonal cumulative precipitation, and an increase in daily precipitation. In spite of the similar input, the response of the two sites, lying respectively on saturated clays and on unsaturated non-plastic silts, might be completely different. Although these studies do not currently provide quantitative estimates, they represent a valuable support to policy makers and communities for the definition and prioritization of adaptation actions and for investments to cope with the expected climate changes.

The Role of the Precipitation History on Landslide Triggering in Unsaturated Pyroclastic Soils

A wide area around the town of Naples is mantled by shallow unsaturated volcanoclastic soils that are highly susceptible to fast rainfall-induced flow-like landslides. Some casualties and huge damage recorded in the last twenty years testify the serious threat posed by such events. Due to the impact of these phenomena, the local research community is strongly committed in studies whose results have allowed to understand some key aspects of the triggering and propagation mechanisms. However, the way to run for risk mitigation is still long: given the density of population and of infrastructure, the setting up of reliable early warning systems would be a fundamental tool to this aim. Based on a rich data-base about the features of the rainfall-induced landslides in unsaturated volcanoclastic soils occurred on January, 10th, 1997, in a small area located in the Sorrento peninsula, and the history of precipitations occurred in the same area in the last fifty years, the paper examines the relation between rainstorms and landslides, showing the fundamental role of the recent precipitation history.