Modeling Debris-Covered Glacier Dynamics in the Karakoram Himalaya
Published in Texas A&M University (Doctoral dissertation), Huo, D., 2020
Abstract: Recent studies have not achieved a general consensus on how debris-covered glaciers (DCGs) in the central Karakoram Himalaya respond to climate change. Many climate-glacier dynamics cannot be explained by existing models due to the use of oversimplified parameterizations and inappropriate assumptions. This research focuses on improving numerical models for DCGs and understanding the nature of DCG dynamics using simulations to provided new insights into the sensitivity of a DCG system to radiative forcing in the central Karakoram. Simulations based on the Baltoro Glacier in the central Karakoram indicate that the variability in surface ablation on a DCG is regulated by the feedbacks between surface morphology, melting, and debris flux. The topographic influence on surface ablation is non-negligible for DCGs because surface topography controls irradiance and debris thickness distribution. Results also highlight the importance of debris thickness and gravitational debris flux in governing surface ablation. Supraglacial lake simulations over the ablation zone of the Baltoro Glacier suggest that supraglacial lakes make a significant contribution (more than 20%) to the total ice-mass loss over the ablation season. Gravitational debris flux and surface topography control lake development, and the presence of supraglacial lakes increases the nonlinearity of the glacier’s response to radiative forcing, which are represented as an acceleration in ablation rate, total ice-mass loss, and the lowering of surface altitude over the ablation season. Simulation results suggest that DCGs in the central Karakoram are actively responding to radiative forcing. The positive feedback between supraglacial lake expansion and ablation may be the main cause for many critical transitions found in temporal and spatial variations in ablation, lake volume, ice volume, ice-flow speed, and mass balance. Collectively, simulations show that even though the magnitude of ice loss on a debris-free glacier is typically higher, the subsystems of a DCG show more critical state transitions and higher spatio-temporal variability, which suggest that DCGs are more sensitive to radiative forcing than previously thought, and some DCGs may exhibit higher sensitivity to climate forcing than debris-free glaciers.