The impacts of the accelerated glacier retreat in recent decades on glacier runoff changes are still unknown in most Andean catchments, increasing uncertainties in estimating water availability. This particularly affects the outer tropics and Dry Andes, heavily impacted by prolonged droughts. Current global estimates overlook climatic and morphometric disparities, which significantly influence model parameters, among Andean glaciers. Meanwhile, local studies have used different approaches to estimate glacier runoff in a few catchments. Improving 21st-century glacier runoff projections relies on calibrating and validating models using corrected historical climate inputs and calibrated parameters across diverse glaciological zones. Here, we simulate glacier evolution and related runoff changes between the periods 2000–2009 and 2010–2019 across 786 Andean catchments (11 282 km² of glacierized area, 11° N to 55° S) using the Open Global Glacier Model (OGGM). TerraClimate atmospheric variables were corrected using in situ data, getting a mean temperature bias by up to 2.1 °C and enhanced monthly precipitation. Glacier mass balance and volume were calibrated, where melt factor and the Glen A parameter exhibited significant alignment with varying environmental conditions. Simulation outcomes were validated against in situ data in three documented catchments (with a glacierized area > 8 %) and monitored glaciers. Our results at the Andes scale reveal an average reduction of 8.3 % in glacier volume and a decrease of 2.2 % in surface area between the periods 2000–2009 and 2010–2019. Comparing these two periods, glacier and climate variations have led to a 12 % increase in mean annual glacier melt (86.5 m³ s⁻¹) and a decrease in rainfall on glaciers of −2 % (−7.6 m³ s⁻¹) across the Andes, with both variables comprising the glacier runoff. We confirmed the utility of our corrected regional simulations of glacier runoff contribution at the catchment scale, where our estimations align with previous studies (e.g., Maipo 34° S, Chile) as well as provide new insights on the seasonal glaciers' largest contribution (e.g., La Paz 16° S, Bolivia) and new estimates of glacier runoff contribution (e.g., Baker 47° S, Chile).

Over the last decades, glaciers across the Andes have been strongly affected by a loss of mass and surface areas. This increases risks of water scarcity for the Andean population and ecosystems. However, the factors controlling glacier changes in terms of surface area and mass loss remain poorly documented at watershed scale across the Andes. Using machine learning methods (Least Absolute Shrinkage and Selection Operator, known as LASSO), we explored climatic and morphometric variables that explain the spatial variance of glacier surface area variations in 35 watersheds (1980–2019), and of glacier mass balances in 110 watersheds (2000–2018), with data from 2,500 to 21,000 glaciers, respectively, distributed between 8 and 55°S in the Andes. Based on these results and by applying the Partitioning Around Medoids (PAM) algorithm we identified new glacier clusters. Overall, spatial variability of climatic variables presents a higher explanatory power than morphometric variables with regards to spatial variance of glacier changes. Specifically, the spatial variability of precipitation dominates spatial variance of glacier changes from the Outer Tropics to the Dry Andes (8–37°S) explaining between 49 and 93% of variances, whereas across the Wet Andes (40–55°S) the spatial variability of temperature is the most important climatic variable and explains between 29 and 73% of glacier changes spatial variance. However, morphometric variables such as glacier surface area show a high explanatory power for spatial variance of glacier mass loss in some watersheds (e.g., Achacachi with r² = 0.6 in the Outer Tropics, Río del Carmen with r² = 0.7 in the Dry Andes). Then, we identified a new spatial framework for hydro-glaciological analysis composed of 12 glaciological zones, derived from a clustering analysis, which includes 274 watersheds containing 32,000 glaciers. These new zones better take into account different seasonal climate and morphometric characteristics of glacier diversity. Our study shows that the exploration of variables that control glacier changes, as well as the new glaciological zones calculated based on these variables, would be very useful for analyzing hydro-glaciological modelling results across the Andes (8–55°S).

Using an ensemble of close- and long-range remote sensing, lake bathymetry and regional meteorological data, we present a detailed assessment of the geometric changes of El Morado Glacier in the Central Andes of Chile and its adjacent proglacial lake between 1932 and 2019. Overall, the results revealed a period of marked glacier down wasting, with a mean geodetic glacier mass balance of −0.39 ± 0.15 m w.e.a⁻¹observed for the entire glacier between 1955 and 2015 with an area loss of 40% between 1955 and 2019. We estimate an ice elevation change of −1.00 ± 0.17 m a⁻¹for the glacier tongue between 1932 and 2019. The increase in the ice thinning rates and area loss during the last decade is coincident with the severe drought in this region (2010–present), which our minimal surface mass-balance model is able to reproduce. As a result of the glacier changes observed, the proglacial lake increased in area substantially between 1955 and 2019, with bathymetry data suggesting a water volume of 3.6 million m³in 2017. This study highlights the need for further monitoring of glacierised areas in the Central Andes. Such efforts would facilitate a better understanding of the downstream impacts of glacier downwasting.

Glaciers are retreating globally and are projected to continue to lose mass in the coming decades, directly affecting downstream ecosystems through changes in glacier runoff. Estimating the future evolution of glacier runoff involves several sources of data uncertainty, which to date have not been comprehensively assessed on a regional scale. In this study, we used the Open Global Glacier Model (OGGM) to estimate the evolution of each glacier (with area > 1 km²) in the Patagonian Andes (40–56° S). As sources of uncertainty, we used different glacier inventories (n = 2), ice thickness datasets (n = 2), historical climate datasets (n = 4), general circulation models (GCMs; n = 10), emission scenarios (Shared Socioeconomic Pathways, SSPs; n = 4) and bias correction methods (BCMs; n = 3) to generate 1920 possible scenarios over the period of 1980–2099. In each scenario, glacier runoff and melt time series were characterised by 10 glacio-hydrological signatures (i.e. metrics). We used the permutation feature importance of random forest regression models to assess the relative importance of each source of uncertainty on the signatures of each catchment. Considering all scenarios, 34 % ± 13 % (mean ± 1 standard deviation) of the glacier area has already peaked in terms of glacier melt (the year 2020), and 68 % ± 21 % of the glacier area will lose more than 50 % of its volume this century. Considering the glacier melt signatures, the future sources of uncertainty (GCMs, SSPs and BCMs) were the main source in only 17 % ± 21 % of the total glacier area. In contrast, the reference climate was the main source in 69 % ± 22 % of the glacier area, highlighting the impact of calibration choices on baseline conditions, model parameters and the initial starting geometry for future projections. The results provide a basis for prioritising future efforts (e.g. the improvement of reference climate characterisation) to reduce glacio-hydrological modelling gaps in poorly instrumented regions such as the Patagonian Andes.

Assessing future water contributions from glaciers is crucial for managing water resources, preventing disasters, and protecting ecosystems and communities. However, Andean glacier runoff remains poorly understood because of missing regional and local research studies. We evaluated eight CMIP6 models (1990–2049), projected future changes in glacier runoff (2030–2049) and peak water throughout the 21st century in 778 Andean catchments (11°N-55°S), using the Open Global Glacier Model (OGGM) under two extreme climate change scenarios (SSP1-2.6 and 8.5). Projections for the mid-21st century show warming trends across the Andes, particularly in the Tropical Andes (+ 0.7 °C), while precipitation declines slightly in the Southern Andes (-1 to -3%). These changes significantly impact glacier runoff, with substantial decreases projected for the Tropical Andes (-43%) and Dry Andes (-37%) by 2030–2049. Notably, changes in glacier runoff vary greatly across the Dry Andes, as evidenced by the simulations for the Atuel (-62%) and Tupungato (+ 32%) catchments in Argentina. More than 95% of Andean catchments are expected to reach peak water before 2030 (75th percentile), with significant regional differences. Our study highlights the critical need to examine regional disparities in glacier runoff at the catchment scale, particularly in the Dry Andes of Chile and Argentina. It calls on these governments to actively fund hydrological research in this region, which is essential for effectively managing current and future water resources.