The Importance of a Glacier Complex for Downstream Runoff in the Semiarid Chilean Andes During Dry Years

Abstract

High mountain catchment systems are inherently complex and include multiple processes that influence runoff generation, making it challenging to assess their current state and project their future solely based on observed data. However, combining observations with hydrological models that can simulate glacio-hydrological processes robustly offers a solution to this issue. This study focused on analysing and characterising the snow, glacier and runoff processes of the Tapado Glacier sub-catchment, an upstream source of the La Laguna reservoir in the semiarid Chilean Andes (30° S) for 2019–2021. For this purpose, a semi-distributed physical model (Cold Regions Hydrological Model [CRHM]) was used to simulate glacio-hydrological processes. The results indicate that sublimation accounted for 66%–89% of snow ablation, limiting the amount of snow available for melting in summer, and making melt from Tapado Glacier the primary component of mid-summer (January) discharge (28%–55%). This was reflected in significant mass loss from the Tapado Glacier ablation zone (−0.5 to −2.1 m w.e.). Sensitivity analyses indicated that precipitation and snow roughness generated the greatest variability in simulations related to snow mass balance process. Uncertainty due to errors in precipitation measurement and extrapolation is inherent in hydrological modelling in most mountain settings, whilst the uncertainty related to snow roughness (evaluated range: 0.0001–0.1 m) is largely due to its direct influence on snow sublimation rates and the challenges associated with measuring this variable. For the glaciated areas, results were sensitive to the selection of ice albedo. Whilst the Tapado sub-catchment includes only 1% of the catchment feeding the La Laguna reservoir (c.a. 27 km downstream), it equates to 6%–26% of monthly inflow into the reservoir over the study period. This indicates the importance of glaciated regions for supporting baseflow during relatively dry periods.