Understanding Climate-Glacier Dynamics in the Karakoram Himalaya using Debris-Flux and Ablation Modeling

Debris-covered glacier ablation dynamics are governed by climate, topography, debris flux, melt-water production and supraglacial lake evolution. Recent studies show that debris-covered glaciers can have ablation rates comparable to bare-ice glaciers, and exhibit accelerated downwasting, despite insulation effects of thick debris loads that are thought to restrict melting. One shortcoming of existing ablation models is the over-simplification of ablation dynamics and surface conditions that may not account for supraglacial sediment flux, topographic effects on surface irradiance, debris properties (thickness, lithology, and albedo), meltwater transport and supraglacial lake evolution. We address this using an improved glacier ablation model that more fully characterizes ablation dynamics by accounting for temporally linked radiative forcing, topographic and morphological evolution as well as sediment fluxes. Simulation results based on the Baltoro Glacier in the central Karakoram Himalaya indicate that debris load variability and supraglacial lake distribution strongly control the differential surface downwasting, with supraglacial debris fluxes being a significant factor that governs supraglacial debris thickness redistribution over the ablation season. Results also demonstrate that glacier surface conditions, such as topography, debris lithology and the presence of water exhibit high spatial and temporal variability over an ablation season, which also contributes to the differential surface melting. Furthermore, feedback mechanisms involving surface melting, debris flux and topographic evolution locally accelerate melting and therefore govern glacier sensitivity to change. Consequently, the debris-covered glaciers in the Karakoram may be more sensitive to climate change than previously thought, given the high degree of differential downwasting and the active feedback between surface ablation, surface morphology, debris flux and supraglacial lake evolution.