Glacio-hydrological changes along the Andes throughout the 21st Century

Assessing future glacier water contributions is crucial for resource management. However, a large gap persists regarding Andean glacier runoff research. We evaluated eight CMIP6 models (1990-2049) on a glacierized area of 27,669 km², and projected future changes in glacier runoff (on 11,282 km² related to land-terminating glaciers) using an evaluated glaciological model in 778 catchments under two extreme SSP scenarios to estimate the year of maximum glacier runoff (peak water). We evaluated the different GCMs over the historical period using in situ data and showed that some of them perform better in specific glaciological regions. For the mid-21st century, warming trends are projected across the Andes, especially in the Tropical Andes (+0.7°C), while precipitation is expected to decrease slightly in the Southern Andes (-1 to -3%). These variables significantly affect glacier dynamics and runoff estimates. Glacier runoff estimates spanning 2000-2019 and projected to 2030-2049 indicate significant declines in the Tropical Andes (-43%) and Dry Andes (-37%), and a lesser decrease in the Wet Andes (-32%). Notably, the Atuel (-62%) and Tupungato (+32%) catchments in the Dry Andes show highly contrasted changes in annual runoff across the Andes. In terms of peak water, most catchments are expected to reach it before the first half of the 21st century (between 2010 and 2028). Our study underlines the critical importance of considering seasonal variations when analyzing GCMs in hydro-glaciological simulations and emphasizes regional disparities in glacier runoff across the Andes for future water resources management.