Abstract
<title>Abstract</title> <p>Andean basins face high vulnerability to climate change, threatening regional water security. The Condoroma Dam, in the western Cordillera Occidental of southern Peru, on the upper Colca River (Arequipa region), regulates the Majes-Siguas system with a storage capacity of 260 hm³. This study assesses future water availability under climate-change scenarios using the GR4J hydrological model, calibrated via the PSO algorithm and forced with CMIP6 projections under SSP2-4.5 and SSP5-8.5 for the near-future (2030–2060) and far-future (2070–2100) horizons. CMIP6 global climate models were evaluated against the PISCO gridded product during the historical period (1981–2014). The best-performing models were selected using the TOPSIS multi-criteria method, followed by bias correction via Quantile Delta Mapping. Results show mean annual precipitation rising from historical values of 600–800 mm/yr to 700–1000 mm/yr in the near future and 800–1400 mm/yr by century's end, with substantial uncertainty under SSP5-8.5. Mean annual temperature increases steadily, from 6.0–7.0°C historically to 7.0–8.0°C in the near future and 9.0-9.5°C by the far future, with extremes exceeding 11.0°C. Water availability shows moderate increases in the wet season, but much sharper changes in the dry season, reaching up to 138.15% under SSP5-8.5. This study offers a methodological framework and evidence of future climatic and hydrological risks, providing a replicable model for reservoir management in similar contexts. It also contributes to a better understanding of climate change impacts on water availability in high-altitude Andean basins.</p>