Effects of climate change on hydrology and hydropower systems in the Italian Alps

In this study we assess the impact of climate change on the hydrological cycle of an Alpine catchment and on the management of hydropower systems. We apply the traditional climate change impact study approach, known in the literature as “scenario-based” approach, to the case study of Lake Como catchment. The “scenario-based” approach consists in employing a modelling chain, which comprises the definition of Green House Gases emission scenarios, the simulation of climate models and hydrological models, and the simulation of the impact on water resources. We take into account an ensemble of climate scenarios, comprising two Representative Concentration Pathways (RCPs), seven General Circulation Models (GCMs) and five Regional Circulation Models (RCMs). The analysis of the climate scenarios on the domain of interest shows an increase in temperature and a seasonal shift in precipitation, causing drier summers and more rainy winters. We apply a statistical downscaling to the climate scenarios in order to match the adequate spatial resolution needed for hydrological modelling. We adopt Topkapi-ETH, a physically-based and fully distributed hydrological model, to reproduce the response of the catchment hydrology to climate change. The employment of a spatially distributed model is due to the possibility of assessing the impact of climate change on different areas of the catchment. Moreover, Topkapi-ETH allows to simulate anthropogenic infrastructures such as reservoirs and river diversions, which are widely present in the Lake Como catchment. The simulation results over the XXI century scenario show a seasonal shift in the hydrological cycle, with lower flow in summer, higher flow in winter, and an earlier snowmelt peak. This results in different patterns of storage building in the Alpine hydropower reservoirs. Finally, we analyze the uncertainty on hydro-climatic variables associated to climate modelling. Results show that the uncertainty related to the choice of the GCM is the most critical, but comparable to the one of the RCM. The choice of the RCP is generally less crucial for short lead times, but it increases in relative terms for longer lead times.