Spatial modelling of solar irradiation and evapotranspiration for the improvement of the cultivation of Artemisia umbelliformis in Aosta Valley

Artemisia umbelliformis, traditionally used to produce the genepì liqueur, represents one of the most valuable non-timber alpine resources in the Western Alps. This study presents an innovative methodology of modelling solar irradiation and evapotranspiration, considering the complex topography of the Aosta Valley (Italy) in as much detail as possible to improve the use and cultivation of the herbaceous plant. Starting from high-resolution digital elevation models (2 m x 2 m) and using ArcGIS “Raster/Area Solar Radiation”, the spatial and temporal modelling of solar irradiation in the area of agricultural interest was performed, incorporating aspect, slope and topography shading, thanks to the calibration of atmospheric transmissivity and diffusivity coefficients against PVGIS data. The resulting layers were coupled with FAO-56 Penman–Monteith methods for the calculation of terrain-aware reference evapotranspiration (ETo). By approximating the correct crop coefficient and thus obtaining the potential evapotranspiration, the study estimated the water demand of each cultivated field and consequently the irrigation requirement for the month under consideration. Results show that the already existing Artemisia umbelliformis fields correspond to micro-areas characterized by higher solar exposure and evapotranspiration compared to the average in the study area, which indicates favourable exposure and microclimatic conditions. This methodology represents a replicable approach for assessing water balance and cultivation suitability in alpine environments, evaluating both the already existing fields of the cultivation of interest as well as suitable future cultivation areas.