Hydrological Response of Andean Catchments to Recent Glacier Mass Loss

Abstract. The impacts of the accelerated glacier retreat in recent decades on runoff changes are still unknown in most Andean catchments, thereby increasing uncertainties in estimating and managing water availability. Here, we used a monthly time step to simulate glacier evolution and related runoff changes for 36 % of the glacierized surface area of the Andes (11,282 km² in 786 catchments, 11° N–55° S) using the Open Global Glacier Model (OGGM) and a corrected and evaluated version of the TerraClimate dataset between 2000 and 2019. The glacier mass balance and volume were calibrated glacier-by-glacier. The simulation results were evaluated with in situ data in three documented catchments and 15 glaciers. Our results show that the glacier volume (−8.3 %) and surface area (−2.2 %) are reduced in 93 % of the catchments between the periods 2000–2009 and 2010–2019. This glacier loss is associated with changes in climate conditions (precipitation = −9 %; temperature = +0.4 ± 0.1 °C) inducing an increase in the mean annual glacier melt of 12 % (86.5 m³/s) and a decrease in the mean annual rainfall on glaciers of −2 % (−7.6 m³/s). We find a regional pattern in the melt factors showing decreasing values from the Tropical Andes toward the Wet Andes. A negative mass balance trend is estimated in the three documented catchments (glacierized surface area > 8 %), showing the largest mean glacier contribution during the transition season (September–November) in La Paz (Bolivia) (45 %) followed by Baker (Chile) (43 %) and Maipo (Chile) (36 %) during the summer season (January–March). In addition, our evaluation in the monitored glaciers indicates an underestimation of the mean simulated mass balance by 185 mm w.e. yr⁻¹ and a high mean correlation (r = 0.7). We conclude that the large increases in the simulated glacier melt in the Dry Andes (36 %) and the Tropical Andes (24 %) have helped to improve our knowledge of the hydro-glaciological characteristics at a much wider scale than previous studies, which focused more on a few select catchments in the Andes.