Possible response of two water systems in central Italy to climatic changes

Aiming to building realistic possible scenarios of the impacts of the ongoing climate change on the hydrologic systems of Central Italy, a rainfall-runoff model was used to simulate two strategic water systems. The model, made by several tanks in series and adapted to the specific investigated systems, was applied to the Trasimeno Lake to simulate its levels and to Bagnara spring to simulate its discharge; the model works at a monthly scale. In both cases the model was properly calibrated and validated over different sets of lake levels and spring discharge data. The calibrated models have been then used to simulate the systems behaviour under different climatic scenarios; these scenarios were set in accordance with the indications obtained by the analysis of historical rainfall and temperature series recorded in the systems surroundings. For the Trasimeno Lake the model indicates that in about two decades the lake would seasonally get dry if the yearly rainfall would decrease by - 20% with respect to 1984-2006. As for Bagnara spring, simulation shows that a rainfall variation of about -11% with respect to 1989-2009, leads the discharge to decrease of about 17% assuming the temperature to stay constant, and of about 20% considering a positive temperature trend. These results are plausible "scenarios", not forecasts: in spite of this, they demonstrate that the two systems are very sensible even to slight variation of rainfall. Given that in the area, for the next decades, most of the scenarios point towards a decrease of future rainfall, the stakeholders should consider these results when updating the management strategies.