Climate and geomorphologic hazard in Barbera d’Asti Terroir

Climatologic investigations and geomorphologic hazard assessment have been carried out in the territory for the production of the Barbera d'Asti, the most cultivated type of vine in Piedmont, nowadays more and more appreciated (D.O.C. recognition has been decreed on January 1970). The traditional Barbera areas are located in part of Asti and Alessandria districts, on Monferrato hills south to the Po River. Barbera vineyards presently cover almost 15 thousand hectares of countryside in the Monferrato hills alone. They grow on terrains belonging, from a geological point of view, to the tertiary Piedmont basin (an Oligocene-Miocene sedimentary succession prevalently composed by alternating sandstones and mudstones) and to Pliocene marine deposits (Lugagnano clays and Astian sands). For a best knowledge of Barbera d'Asti terroir, it is fundamental to characterize its climatic and geomorphologic features. Quality and peculiarity of any wine are tightly related to the climate typologies. Climatic variations cause wine peculiarity differentiations in both space and time, on the micro- and meso-climatic scale. By considering temperature as the most important parameter for vegetative-productive vine development, the study area has been classified as a cold type terroir. The threshold is imposed by the 10°C isotherm. The climatic analysis has taken into account the parameters conditioning the vine phenologic stages such as: mean number of freeze-days, thermal summation, relative humidity, seasonal effect of rainfall. Among the elements of climate, intensive precipitations (rainstorm) have been investigated in order to assess the landslide hazard in the Barbera areas. Although monocline structure and fluvial erosion predispose slopes to translational slides, the most frequent landslide typology recorded in the area, is soil slip: a type of landslide involving small sections of superficial weakly-bonded soil, usually triggered by brief, heavy rainfall. These phenomena mostly occur on slopes composed of a lithoid substrate and a superficial layer of very different permeability characteristics (i.e. an eluvio cofluvial cover). Soil slips are characterized by a triggering stage as a shallow slide and by subsequent development generally occurring as a flow. Soil Slip Susceptibility Maps have been created in the territory for the production of the Barbera d'Asti by using Green-Ampt equations governing the infiltration of water in the soil as a wetting front and Fredlund relations for the shear strength in an unsaturated soil. For the model implementation, hydrological, morphological and physical-mechanical attributes have been considered such as rainfall rate and duration, slope (50-meter DEM cells), hydraulic conductivity, porosity, effective porosity and initial effective saturation of soil, wetting front soil suction head, etc The numerical approach allows to evaluate the relationship between the rainfall rate and duration and the slope stability at different hydrological soil conditions. The reliability of the model products depends on the quality and the quantity of the opening information, such as a DEM suitable for studies on local level. Furthermore, these methodologies allow to integrate future data, improving the system. The realized maps can be useful in risk analysis for evaluating economic losses on wine annual production.