Quantifying Ablation Dynamics in the Debris-Covered Zone of Panchinala-A Glacier Using High-Resolution UAV Photogrammetry

The heterogeneous ablation rates of debris-covered glaciers strongly influence mass balance and melt patterns, yet the factors controlling this variability remain poorly understood. To understand this, this study quantifies ablation dynamics across the debris-covered zone of Panchinala A glacier, located in western Himalaya, India, using high-resolution unmanned aerial vehicle (UAV) photogrammetry data. Multi-temporal UAV surveys were conducted during ablation seasons of 2021 and 2022 to generate orthomosaics and digital elevation models (DEMs) at centimeter-scale resolution. Surface velocity was estimated using the More Global Matching algorithm implemented in the Ames Stereo Pipeline and combined with independent ice thickness estimates to compute flux divergence. Flow-corrected Lagrangian surface mass balance (SMB) was estimated using a continuity-equation approach, applying mass conservation under an assumption of constant ice density. During 2021–2022, the ablation area exhibited a mean horizontal velocity of 4.40 m a⁻¹; velocities decreased progressively along-flow toward the glacier front. The mean Lagrangian SMB across the ablation area was -602.6 kg m^-² a^-1 (2021–2022). The result indicates contrasting ablation patterns over ice cliffs and debris covered area. Ice cliffs and adjacent ablation hotspots (10 m buffer) contributed ~50% of total ablation while occupying ≤20% of the ablation area, whereas the remaining debris-covered surface (~80%) accounted for ~50%. These results show that high-resolution datasets are important for accurate surface mass balance estimation and for resolving the spatial heterogeneity of ablation on debris-covered glaciers.