Reimagining how Andean glaciers buffered past streamflow droughts

Climate change intensifies water scarcity by increasing the frequency of streamflow droughts. Glaciers play a key role in moderating these events by regulating runoff, but their ongoing retreat threatens this natural resilience. Despite case-specific advances, the regional role of Andean glaciers in shaping streamflow droughts across complex climates and landscapes remains highly uncertain. To address this gap, we use a hybrid glacio-hydrological model that combines process-based glacier mass-balance and ice-flow dynamics with a data-driven runoff representation, allowing us to capture both long-term glacier evolution and short-term hydrological responses. This model is applied to a newly developed dataset of 257 glacierized catchments spanning the Andes (“AndeanGC”; 5–56ºS), which consolidates harmonized hydrological observations, remotely sensed glacier characteristics, and gridded meteorological forcing. The hypothetical future glacier extents correspond to projections under three warming storylines that represent plausible global outcomes: a Paris-aligned pathway limiting warming to 1.5 °C, a current-policy trajectory leading to approximately 2.8 °C of warming, and a high-emission pathway reaching about 4.0 °C. We find that glaciers historically provided substantial buffering of streamflow droughts, but this effect diminishes as glaciers shrink. If past droughts had occurred under the smaller glacier extents projected for the late 21st century under current climate policies, their severity and spatial extent would have increased substantially. Consequently, regional water stress would have intensified markedly. These hypothetical scenarios reveal the previously unquantified regional influence of glaciers on past droughts and illustrate the broader consequences of their decline for water resources. They also highlight the critical need to communicate these changes effectively to support climate-resilient planning and policy.