McCarthy, Michael, Meier, Fabienne, Fatichi, Simone, Stocker, Benjamin D., Shaw, Thomas E., Miles, Evan, Dussaillant, Inés, and Pellicciotti, Francesca
The current Chilean megadrought has led to acute water shortages in central Chile since 2010. Glaciers have provided vital fresh water to the region's rivers, but the quantity, timing and sustainability of that provision remain unclear. Here we combine in‐situ, remote sensing and climate reanalysis data to show that from 2010 to 2018 during the megadrought, unsustainable imbalance ablation of glaciers (ablation not balanced by new snowfall) strongly buffered the late‐summer discharge of the Maipo River, a primary source of water to Santiago. If there had been no glaciers, water availability would have been reduced from December through May, with a 31 ± 19% decrease during March. Our results indicate that while the annual contributions of imbalance ablation to river discharge during the megadrought have been small compared to those from precipitation and sustainable balance ablation, they have nevertheless been a substantial input to a hydrological system that was already experiencing high water stress. The water‐equivalent volume of imbalance ablation generated in the Maipo Basin between 2010 and 2018 was 740 × 106 m3 (19 ± 12 mm yr−1), approximately 3.4 times the capacity of the basin's El Yeso Reservoir. This is equivalent to 14% of Santiago's potable water use in that time, while total glacier ablation was equivalent to 59%. We show that glacier retreat will exacerbate river discharge deficits and further jeopardize water availability in central Chile if precipitation deficits endure, and conjecture that these effects will be amplified by climatic warming. Plain Language Summary: Since 2010, central Chile has experienced a long period of drought or "megadrought." There has been considerably less water in rivers and streams, causing a wide range of societal problems. In our study, we explore the role glaciers have played in maintaining river levels during the megadrought. We focus on the basin of the Maipo River, from which the Chilean capital Santiago derives a large portion of its water supply. Our results suggest that meltwater from the glaciers has been much less sustainable since the megadrought began in 2010, and that if there had been no glaciers, water availability during the megadrought would have been substantially reduced in late summer. We found that even without the seasonal snow that falls on them, glaciers provided enough meltwater from 2010 to 2018 to meet 14% of Santiago's potable water use. Given predictions of a drier future in central Chile, our results have implications for the water resilience of the Chilean capital, its agricultural sector, and the health of its upstream mountain ecosystems. Key Points: Imbalance glacier ablation has strongly buffered the late‐summer discharge of the Maipo River during the current Chilean megadroughtBetween 2010 and 2018, almost a quarter of total glacier ablation in the Maipo Basin was not balanced by new snowfallBy buffering river discharge during drought, glaciers, distinct from seasonal snow, provide a valuable hydrologic service to Santiago [ABSTRACT FROM AUTHOR]