Recent advances in vadose zone hydrology: The contribution to a better understanding of hydrologically triggered shallow landslides.

Land has suffered from and always will be exposed to natural events and human activities leaning toward its alteration. Several zones of the World now show even severe land degradation phenomena, which are chiefly driven by overexploitation beyond their carrying capacity or are due to the implementation of management practices not always optimal and consistent with the local environmental conditions. Land degradation and the occurrence of landslides are complex phenomena that bring into play interdependencies and interactions among several physical processes, such as hydrology, soil and vegetation dynamics, climate, etc. . Allowing for the specific theme of this workshop, now more than ever before there is a need to gain a better understanding of potential failure conditions of vegetated slopes causing hydrologically triggered shallow landslides. Soil and water provide the media for ecohydrological processes and mathematical models of different complexity have been developed for describing these processes. Although progress has been achieved in advancing scientific knowledge on the soil-vegetation-atmosphere (SVA) system as well as in developing improved monitoring and modeling techniques, difficulties still exist in exploiting these results by decision makers and stakeholders that should plan suitable and effective interventions to protect the environment. This talk would firstly review and provide a critical account of some laboratory and field experiments. A discussion will follow on how and to what extent this information can be suitably implemented in computer models describing the evolution of processes in the SVA system. This represents a valuable basis to throw ourselves toward challenging questions in vadose zone hydrology, such as the “scale-transfer” and model over-parameterization problems, with related problems of parameter non-uniqueness and uncertainty of the simulations. Laboratory experiments on soil cores and columns provide confirmation of theories and enable soil hydraulic characteristics to be identified more accurately. Investigations carried out at plot, transect, and catchment scales provide insights into the hydraulic response of field soils and help in understanding how small-scale measurements can provide information about larger scale SVA processes. Hydrologically triggered shallow landslides show specific features in landslide-prone regions, such as those under a Mediterranean climate, where conditions of climatic seasonality coupled with some local “shock” (such as wildfires) can make the assessment of slope stability a rather difficult and delicate problem to be tackled.