Ayala et al. (2025) Less water from glaciers during future megadroughts in the Southern Andes

Identification

• Journal: Communications Earth & Environment
• Year: 2025
• Date: 2025-11-18
• Authors: Álvaro Ayala, Eduardo Muñoz‐Castro, Daniel Farinotti, David Farías-Barahona, Pablo A. Mendoza, Shelley MacDonell, James McPhee, Ximena Vargas, Francesca Pellicciotti
• DOI: 10.1038/s43247-025-02845-6

Research Groups

• Center for Advanced Studies in Arid Zones (CEAZA), La Serena, Chile
• Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Birmensdorf, Switzerland
• Department of Civil Engineering, Universidad de Chile, Santiago, Chile
• WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland
• Climate Change, Extremes and Natural Hazards in Alpine Regions Research Center CERC, Davos Dorf, Switzerland
• Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland
• Laboratory of Hydraulics, Hydrology and Glaciology (VAW), ETH Zurich, Zurich, Switzerland
• Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), bâtiment ALPOLE, Sion, Switzerland
• Department of Geography, Universidad de Concepción, Concepción, Chile
• Advanced Mining Technology Center (AMTC), Universidad de Chile, Santiago, Chile
• Waterways Centre, University of Canterbury and Lincoln University, Christchurch, New Zealand
• Institute of Science and Technology (ISTA), Klosterneuburg, Austria

Short Summary

This study assesses the hydrological response of Southern Andes glaciers to the current Chilean megadrought (2010-2019) and projected end-of-century megadroughts using glacio-hydrological simulations. It finds that while glaciers buffered water supply during the current drought by losing 10% of their volume, their buffering capacity will significantly decline in future megadroughts due to massive ice loss, leading to substantial reductions in glacier runoff.

Objective

• To assess the hydrological response of glaciers in the Southern Andes to the ongoing Chilean megadrought (2010-present) and to projected end-of-century megadroughts, specifically examining their capacity to sustain water discharge and buffer precipitation deficits.

Study Configuration

• Spatial Scale: 100 largest glaciers (113 individual glacier polygons) in the Southern Andes between 30°S and 40°S, covering a total area of 1044 square kilometers and an initial ice volume of 82.0 cubic kilometers. Model simulations were run at a 100 meter horizontal resolution.
• Temporal Scale:
  • Historical/Reference Period: 2000–2009
  • Current Megadrought Analysis: 2010–2019 (sub-period of the Chilean megadrought)
  • Future Projections: 2000–2099, with end-of-century megadroughts defined as the driest 10-year periods during 2075–2100. Model simulations were run at a 3 hour time step.

Methodology and Data

• Models used:
  • Glacio-hydrological model: TOPKAPI-ETH (physically oriented, spatially distributed, simulates mass balance, evolution, runoff, snow accumulation, snow-ice transition, glacier dynamics, snow melt, ice melt, and ice melt under debris).
  • Climate Models (CMIP5 GCMs): CCSM4, CSIRO-MK3-6-0, IPSL-CM5A-LR, MIROC-ESMI for Representative Concentration Pathways (RCP) 2.6 and 8.5 scenarios.
  • Downscaling and Bias Correction: Multivariate Bias Correction for n-dimensions (MBCn) approach.
• Data sources:
  • Glacier outlines: Randolph Glacier Inventory v6.0 (RGIv6.0).
  • Surface topography: Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM).
  • Distributed ice thickness (year 2000): Farinotti et al. (2019).
  • Distributed supraglacial debris thickness: Rounce et al. (2021).
  • Glacier surface elevation changes (for calibration): Hugonnet et al. (2021).
  • Satellite-derived albedo (for calibration): Moderate Resolution Imaging Spectroradiometer (MODIS) MOD10A1 and MYD10A1 snow products.
  • Meteorological forcing (2000–2019): CR2Met v2.0 (daily precipitation and air temperature extremes), ERA5 reanalysis (sub-daily distribution of variables, cloud cover transmissivity).
  • Future climate forcing: Downscaled and bias-corrected outputs from CMIP5 GCMs for RCP2.6 and RCP8.5 scenarios.

Main Results

• Current Chilean Megadrought (2010-2019): Despite a mean annual precipitation deficit of 36 ± 12%, glacier runoff remained almost unaltered (1% decrease) compared to 2000-2009, sustained by a 10% loss of total ice volume. Ice melt increased by 118%, offsetting a 32% decrease in snowmelt. The average glacier mass balance became four times more negative (−0.8 ± 0.5 meters water equivalent per year).
• Extremely Dry Year (2019): Precipitation was 66 ± 23% lower, air temperature increased by 0.9 ± 0.2 °C, and glacier runoff increased by 25%, with ice melt increasing by 390%, buffering severe water scarcity.
• Future Projections (End-of-century megadroughts, 2075-2100):
  • Mean annual temperatures are projected to increase by 1.5 ± 0.3 °C (RCP2.6) and 4.7 ± 0.4 °C (RCP8.5) by 2090-2099.
  • Glacier volume is projected to decrease by 55 ± 6% (RCP2.6) and 78 ± 4% (RCP8.5) by the end of the century.
  • Annual glacier runoff is projected to decline by 10 ± 4% (RCP2.6) and 20 ± 11% (RCP8.5) during end-of-century megadroughts compared to 2000-2009 levels.
  • Summer glacier runoff is projected to decline more severely, by 35 ± 3% (RCP2.6) and 48 ± 6% (RCP8.5).
  • During future driest years, glacier runoff is projected to decrease by 27 ± 4% (RCP2.6) and 35 ± 11% (RCP8.5), indicating an exhaustion of the glacier's water provision capacity, in stark contrast to the 25% increase observed in 2019.

Contributions

• Provides a quantitative assessment of the evolving role of glaciers in buffering megadroughts under 21st-century climate change, highlighting the non-linear and complex dynamics of the cryosphere's response.
• Disentangles the relative contributions of snowmelt, ice melt, and rainfall to runoff in glacierized basins during megadroughts, offering a more detailed understanding than previous studies.
• Emphasizes the high sensitivity of glaciers in the semi-arid Andes to precipitation deficits and albedo changes, underscoring the importance of high-resolution, physics-based modeling that explicitly accounts for surface albedo decay.
• Develops a framework for anticipating future water scarcity scenarios in mountain regions, which are increasingly vulnerable due to glacier retreat and projected increases in drought frequency and severity.

Funding

• Austrian Science Fund (FWF), DOI: 10.55776/16891
• Project MegaWat, funded by the Austrian Science Fund (FWF), Swiss National Science Foundation (SNSF), Centre for the Development of Industrial Technology (CDTI), Dutch Research Council (NWO), National Research Council (CNR), and the European Union’s Horizon Europe Programme under the 2022 Joint Transnational Call of the European Partnership Water4all (Grant Agreement n°101060874)
• Fondecyt Postdoc No. 3190732
• WSL programme ‘Extremes’ through the EMERGE project
• ANID-CENTROS REGIONALES R20F0008
• ANID National Master scholarship year 2020 N°22200599
• Swiss National Science Foundation Grant 200021_214907
• Fondecyt project No. 11200142
• ANID/PIA project No AFB230001

Citation

@article{Ayala2025Less,
  author = {Ayala, Álvaro and Muñoz‐Castro, Eduardo and Farinotti, Daniel and Farías-Barahona, David and Mendoza, Pablo A. and MacDonell, Shelley and McPhee, James and Vargas, Ximena and Pellicciotti, Francesca},
  title = {Less water from glaciers during future megadroughts in the Southern Andes},
  journal = {Communications Earth & Environment},
  year = {2025},
  doi = {10.1038/s43247-025-02845-6},
  url = {https://doi.org/10.1038/s43247-025-02845-6}
}