Streamflow Projections in Valgrosina Valley: Climate Change Calls for Adaptation in the Alpine Region

Climate change is increasingly impacting mountainous regions, emphasising the need for reliable streamflow projections to support adaptive hydropower management. This study focuses on the Valgrosina Valley (Northern Italy) with two main objectives: (i) to project impacts on streamflow under four global warming levels (+1.5°C, +2.0°C, +3.0°C, and + 4.0°C relative to pre-industrial conditions) and to evaluate their effects on gross hydropower potential (GHP); and (ii) to compare the performance of two bias-correction approaches—yearly vs. monthly quantile delta mapping (QDM-y and QDM-mo, respectively)—on hydrological projections. Daily precipitation and temperature timeseries from 21 regional climate models (approximately 12.5 km² resolution) were bias-corrected and downscaled using observed data from the 2005–2020 reference period and then used to drive reference and future simulations that reveal pronounced intra-annual shifts relative to the reference period. Under the most severe warming scenario (+4.0°C), winter flows are projected to increase by approximately +0.5 m³ s⁻¹ (around +300%), while summer flows decline by about −0.7 m³ s⁻¹ (−19% to −20.5%), indicating a strong seasonal redistribution of runoff. Correspondingly, the GHP indicated a summer potential decline of up to 20% in energy production. The QDM-mo bias correction approach performed better than QDM-y in preserving intra-annual variability with 14% and 3% less bias than the observed series for precipitation and temperature, respectively. The results underline the vulnerability of hydropower systems to future climatic changes and emphasise the need for adaptive strategies to ensure sustainable use of water and energy in Alpine environments.