Future hydrology of the cryospheric driven Lake Como catchment in Italy under climate change scenarios

In this paper we analyse the future hydrology of the Lake Como catchment under climate change scenarios. The management of the lake is extremely important because it is needed both to supply water for the irrigation demand of the Po Valley, and to prevent flood risk along the lake shores. The climate variations are affecting the lake operation with negative impacts both on agriculture and hydropower production. The lake dynamics are link to the cryospheric driven upstream basin, and so the use of a model able to assess the water input as related to snow cover processes is a key issue. Accordingly, we use the physically based hydrological model Poli-hydro able to represent the most important process in the cryospheric driven catchment. We set up and calibrated the model against lake inflows during 2002-2018, resulting in a mean error Bias = +2.15%, and a monthly/daily Nash-Sutcliff efficiency, NSE = 0.77/0.64. We then performed a stochastic disaggregation of 3 Global Circulation Models (GCMs) of the most recent Assessment report 6 (AR6) of the IPCC, under 4 different socio-economic pathways (SSPs), from which we derived daily series of rainfall and temperature to be used as inputs for the hydrological model Poli-Hydro. The climate projections show a potential increase of temperature at the end of the century between +0.61°C and +5.96°C, which would lead to a decrease of the total ice volume in the catchment of -50% and -77%, respectively. Future projections show generally an increase of discharge in autumn and winter (November-March) and a reduction in spring and summer (May-September). This is due to the increase of temperature with an increase of liquid precipitation instead of solid precipitation in winter and an anticipation of the snow melt peak at the beginning of spring. Possible consequences are the increase of flood hazard in the winter period and a scarcity of water availability in summer. A new regulation of Lake Como is essential to satisfy stakeholders requests.