Aquifer recharge in the Piedmont Alpine zone: Historical trendsand future scenarios

Abstract. The spatial and temporal variability of temperature, precipitation, actual evapotranspiration and of the related water balance components, as well as their responses to anthropogenic climate change, provide fundamental information for an effective management of water resources. In this study we evaluated the past, present and future quantity of groundwater resources available for drinking supply in the water catchments feeding the about 2.3 million inhabitants of the Greater Turin metropolitan area (North-Western Italy), considering climatologies at the quarterly and yearly timescales. Observed temperature and precipitation data from 1959 to 2017 were analyzed to assess historical trends, their significance and the possible cross-correlations between the water balance components. Regional climate model (RCM) simulations from a small ensemble were analysed to provide mid-century projections of aquifer recharge for the area of interest under two emission scenarios. The analysis over the historical period indicated that the driest areas of the study region displayed negative annual (and spring quarter) trends of the difference between precipitation and actual evapotranspiration. Even close-by watersheds exhibit different behaviors, given the large spatial variability of this area at the edge between the Alps and the Mediterranean region. The analysis of future projections suggested almost stationary conditions for annual recharge, with a slight decrease in the second half of the year. The future trends of drainage are very different across the considered RCM ensemble. The large interannual variability of precipitation was identified as the most relevant risk factor for water management, expected to play a major role also in future decades.