Modeling the impacts of climate trends and lake formation on the retreat of a tropical Andean glacier (1962–2020)

Abstract. Located in Peru’s Cordillera Blanca, the Queshque Glacier (~9.8° S) has experienced nearly continuous retreat since the mid-20^th century. More recently, this trend has accelerated after the glacier transitioned from land to lake terminating. We use observations of glacier surface height change (1962–2008), bed topography, and climatology to evaluate the relative drivers of Queshque’s evolution from 1962–2020. Six Open Global Glacier Model ensemble members differing in climatic sensitivity are calibrated to fit the mass balance rate of -442 mm w.e. a^-1 calculated over the 2008 glacier area between 1962–2008. The models are then used to simulate monthly glacier mass balance over the entire study period and dynamic glacier evolution from 2008 to 2020. The models reproduce a typical outer-tropical glacier mass balance regime, showing continuous ablation throughout the year that increases during the pronounced wet season. Climatological trend analyses along with coupled mass balance and ice flow simulations indicate that temperature has been the predominant driver of mass loss since 2008 and that recent precipitation levels have caused minor dampening of this trend. The strongest negative correlation between temperature and mass balance occurs during the wet season, while a positive correlation between precipitation and annual mass balance is most pronounced during the dry season. The influence of ENSO over mass balance trends appears to decline throughout the study period except during the wettest months, suggesting that wet season Pacific sea-surface temperatures are strong predictors of outer-tropical glacier mass balance variability. Finally, frontal ablation into the newly formed lake began in 2010. This caused ice acceleration at the glacier front, an average mass loss increase of 4 %, and a significant narrowing of the model ensemble mass loss spread. We conclude that while Queshque’s trajectory remained coupled to climatic forcings, the new proglacial lake exacerbated and modified the retreat pattern regardless of the model climate sensitivity.