MODELING GLACIER SURFACE ABLATION DYNAMICS FOR INVESTIGATING DEBRIS-COVERED GLACIER SENSITIVITY TO CLIMATE CHANGE IN THE KARAKORAM HIMALAYA

Debris-covered glaciers can exhibit complex surface-ablation dynamics that are governed by climate; topography; debris load lithology, depth and fluxes; as well as melt-water production and supraglacial lake evolution. It is generally thought that debris-coverd glaciers are not as sensitive to climate change due to debris insulation, although complex ablation dynamics have not been rigorously accounted for. Most modeling efforts do not acount for topographically controlled sediment fluxes, meltwater transport, spectral surface irradiance, debris thermal properties, and supraglacial lake evolution. Most existing ablation models either over-simplify surface conditions or heavily rely on meteorological measurements that do not accurately account for scale-dependent conditions over a glacier. Consequently, we address these issues using an integrated model that accounts for surface irradiance, surface topography, energy balance, debris flux, supraglacial lakes, and melt-water drainage to study surface ablation dynamics of debris-covered glaciers in the Karakoram Himalaya. Specifically, we utilize glacier surface topography from the Shuttle Radar Topography Mission (SRTM, 30 m) digital elevation model, glacier surface cover distributions from satellite imagery, and a spectral solar radiation model to simulate glacier surface evolution. Preliminary results based on a Himalayan glacier indicate that glacier ablation dynamics and rates are highly variable in space and time due to feedback mechanisms that control ice surface evolution, and therefore ablation rates. Our simulations document glacier downwasting, and suggest that debris covered glaciers can be very sensitive to climate change given heterogeneous debris distribution. Simulations also show that supraglacial lakes control the differential lowering of the glacier surface and accelerate downwasting in the ablation zone.