Poster Abstract
A key challenge in predicting future glacier behaviour and dynamics is accounting for the effects of supraglacial debris on debris-covered glaciers, which modifies surface ablation and remains poorly constrained in its extent, thickness, and future evolution. Under climate warming, debris cover is projected to expand up-glacier and form at a faster rate due to the accelerated meltout of englacial debris. Increased landslides and avalanches from mountainsides due to weaker slopes are also predicted to contribute to increased debris cover extent.
Of particular interest is the initial emergence of debris below the equilibrium line, where clean ice transitions into debris-covered ice due to debris meltout. These areas are typically characterised by thin and discontinuous debris, which enhances ice melt due to the non-linear relationship between debris thickness and melt. Such transition areas are understudied at the glacier scale and are often excluded from existing distributed debris thickness datasets. Tracking debris evolution enables a clearer understanding of the transition of a glacier surface from clean to debris-covered ice.
This study applies an energy balance model to retrieve debris thickness across Rongbuk Glacier, Tibet, between 2001 and 2020, using Landsat 7 thermal imagery and ERA5 reanalysis data. A Monte Carlo framework quantifies the uncertainty in debris thickness and the rate at which it is thickening, yielding a novel spatially distributed ‘debris accumulation rate’. Results show that debris is not only thickening in the ablation zone but also in sections of the accumulation zone, suggesting enhanced debris delivery from adjacent mountainsides. Consequently, the concentration of debris entrained in englacial ice may be increasing, resulting in the accelerated development of debris cover independent of, and in addition to, enhanced meltout due to climate warming. Such trends are not captured in most glacier evolution models.
Limitations in energy balance modelling are observed in the upper ablation area, where sparse debris cover is poorly represented in satellite imagery due to sub-pixel discontinuity. Novel methods for resolving sub-pixel fractional debris cover from moderate-resolution thermal data are needed to better constrain debris evolution and improve projections of glacier longevity under climate change.