Unveiling the hydrological response to climate change in the alpine environment: the case study of Valgrosina (northern Italy)

This study focuses on hydrologic modeling of the Valgrosina valley (Italian Alps). It covers an area of about 130 km² ranging from 1200 to 3400 m.a.s.l. and is divided into two main branches: the Sacco valley to the west and the Eita valley to the east, where a dam for hydroelectric exploitation rises at the closure section. The objectives are: - to investigate the performance of Quantile Delta Mapping (QDM) for the spatial statistical downscaling of future climate data in Valgrosina, using radar data as reference and - to evaluate the impacts of climate change on the hydrological regime of the study area for different scenarios. The partially distributed model GEOframe was set up at the daily scale in the study area for the 2005-2020 period. Precipitation data from weather radar were corrected by adding the interpolated rain gauges-radar residuals obtained through the inverse distance weighting method. After GEOframe calibration (KGE>0.70), temperature and precipitation timeseries from 21 Regional Climate Models (RCMs) from the EURO-CORDEX domain were downscaled to investigate possible variations of the hydrological regime of the study area. Four different scenarios at increment of 1.5, 2.0, 3.0, 4.0°C above preindustrial temperatures were considered. Comparing the observed and the reference ensemble series in 2005-2020 period at monthly scale, the downscaling performance by QDM method reported KGE values of 0.39 for precipitation and 0.92 for temperature. The downscaling results revealed an average temperature increase of approximately 3.5°C for the most severe scenario respect to the 2005-2020 reference period. No clear trend was observed for the precipitation pattern, with differences ranging from 4% to 7% compared to the observed data. The corresponding discharge simulations revealed significant alterations in the hydrologic regime. The summer discharge peak in June exhibited average reductions up to 44% and 49% in comparison to the observed discharge (2010-2020) in the eastern and western sector of the study area, respectively. The study contributes to the understanding of local hydrological processes and could inform decision-making processes concerning water resource management and foster the development of adaptive strategies in this area.