Effects of vegetation on hydrological response of silty volcanic covers

Abstract

This work examines the hydrological behaviour of a silty volcanic layer exposed to the atmosphere for three 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 four years. The 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. Since 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 in 2005, the experimental results are used to re-interpret such a landslide, considering the effects of vegetation and referring to a coupled thermo-hydraulic model. The experimental results are used to calibrate the model, and this is then used to interpret around ten years of meteorological variables recorded at the landslide site, including the landslide time. Comparison with interpretations previously made as a bare hypothesis shows how neglecting the effects of vegetation might imply a loss in prediction accuracy of soil state variables related to slope stability.