Waning and Waxing of Mountain Glaciers in South America: A Modeling Approach over Multiple Spatial and Temporal Scales

Abstract

Discarding Antarctic and sub Antarctic regions, the Andes concentrate almost 90% of glacier cover in the Southern Hemisphere. Large data gaps exist here, preventing detailed knowledge on how climate determines glacier behavior. As Andean glaciers are distributed in a latitudinal transect spanning from the northern to the southern tip of the continent, they configure an almost seamless laboratory that facilitates the study of glacier-climate interactions across diverse climates. This Ph.D. dissertation has sought to help to fill the gap of mid to long-term, regionally extensive glacier research in the Andes. The tenet of this work is that, given the lack of continuous, long-term observational information, numerical models are fundamental tools to understand glacier-climate interactions. I first reviewed the literature preferentially concerned to modern glacier-climate modeling along the Andes. I demonstrated that current information on glacier changes and their forcings are scarce, sparse, and insufficient. Such paucity of information and the limitation of available data suggest that an extensive use of glacier models can help to better understand spatial and temporal information on past and present trends. I found a gap at the continental scale where relatively few studies have tried to compare glaciers of different climatic regimes at a unified framework. The corollary of the review was that there are plenty of opportunities to increase the number of studies on glacier modeling. Then, I developed and assessed glacier surface mass balance models to be applied at the continental scale. I performed an inter-comparison assessment between one model based on near surface temperature and another on a surface energy balance. I found that temperature-based models were relatively more sensitive to the climatic input utilized, which in turn may exacerbate their sensitivity to tweaks in parameters such as temperature lapse rate. The energy balance model was then employed to simulate Andean glacier surface mass balance between 1979 and 2009. Results indicated heterogeneous mass balance changes, with a widespread negative trend along the tropical Andes and less strong changes toward the extratropics. I also showed that a conventional temperature-precipitation explanation for mass balance changes did not hold everywhere. Finally, I applied the model to a smaller region in central-north Peru, where the largest concentration of tropical glaciers is located. I combined statistical analyses of reanalysis data, regional climate modeling and glacier mass balance modeling to analyze long-term (30 yrs.) and seasonal changes of glacier surface mass balance. Results implied that temperature is the principal factor controlling glacier changes in the study area, although its actual impact may be indirect or hidden by other processes. Significant correlations between lapse rate, humidity and zonal wind suggested that at low to mid elevations homogenization of temperature has driven longwave incoming energy to be less negative, thus leading the net radiative balance to more positive values. Such change may multiply the impact of albedo, thereby enhancing total ablation. The enhancement of albedo impact on mass balance is a plausible explanation of continuous glacier shrinkage despite detected slowdown in warming and increases in precipitation.