Effects of vegetation on hydrological response of silty volcanic covers

This work examines the hydrological behaviour of a silty volcanic layer exposed to the atmosphere for 3 years under vegetated conditions. The layer was extensively monitored to measure energy fluxes, water fluxes, and internal variables (suction, water content, water storage, and temperature). Measurements were used to build representations of the layer's behaviour patterns depending on its surface covering, comparing the behaviour in vegetated conditions with behaviour observed under bare conditions over the previous 4 years. Results show that during cold-dry periods, differences in terms of fluxes and hydrological variables between the bare and vegetated conditions reduce to negligible levels, but increase significantly during hot-dry and transition periods. As the soil forming the layer was selected to have the same intrinsic and state properties as the layer in a specific rainfall-induced landslide case history that occurred in Nocera Inferiore (South Italy) in 2005, the experimental results are used to re-interpret such a landslide, considering the effects of vegetation and referring to a coupled thermohydraulic model. The experimental results are used to calibrate the model, and this is then used to interpret around 10 years of meteorological variables recorded at the landslide site, including the landslide time. Comparison with interpretations made previously as a bare soil hypothesis shows how neglecting the effects of vegetation might imply a loss in prediction accuracy of soil state variables (suction and water storage) related to the slope stability.