Seven decades of glacier loss on the Nevados de Chillán volcanic complex, Chile

Glaciers on the Nevados de Chillán volcanic complex are rapidly retreating, with anticipated consequences for agroforestry, tourism, and regional human and ecological security. Quantifying their mass balance is critical for understanding current meltwater contributions and for anticipating future water availability as these glaciers continue to shrink. Here we estimate the geodetic mass balance of all 28 documented glaciers on the Nevados de Chillán complex. An uncrewed aerial vehicle (UAV) campaign conducted in March 2024 provided updated elevation data for 11 glaciers on the complex, allowing calculation of volume change from 1954–2024 (70 years). For all 28 glaciers, we analyzed airplane and satellite digital elevation models (DEMs) to estimate volume change from 1954–2025 (71 years). The total glacier area of the complex declined from 16.02 km 2 in 1975 to 2.91 km 2 in 2000 and 1.90 km 2 in 2019, totaling an 88 % reduction over 44 years. Our results show a clear acceleration in glacier mass loss after 2000 for the glaciers surveyed with UAV and satellite data. Mean annual specific mass balance of the whole complex was −0.42 ± 0.20 m w.e. yr −1 from 1954–2000, accelerating to −0.60 ± 0.38 m w.e. yr −1 from 2000–2025, representing an approximately 40 % increase in the rate of mass loss. Over 2000–2025, the Cerro Blanco subcomplex lost mass at −0.70 ± 0.38 m w.e. yr −1 and Glaciar Nevado, the largest glacier on the complex, at −0.72 ± 0.38 m w.e. yr −1 . Significant post-2000 declines in February and March streamflow at the Río Diguillín are consistent with the complex having passed peak water. Regional water resource planning should consider how increasing glacier melt rates on the Nevados de Chillán complex will impact the timing and volume of future water availability.