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Abstract
Pakistan’s Karakoram region has a large variety of glacier types. Equilibrium line altitude (ELA) of alpine or valley glaciers represents mass balance. Field observations for estimation of ELA of the majority of Karakoram’s glaciers are not available due to rugged glacier-covered terrains and lack of climatic data above 5000 masl. Therefore, we applied the hypsometrically controlled accumulation area ratio (AAR) and accumulation area balance ratio (AABR) methods for ELA estimation and glacier–climate reconstructions in the Shigar River Basin of the Karakoram region. Constrained by mountain topography, larger size and type of glaciers, several ranges of ELA are calculated and implemented for several ratios. Two parameters (ratio and interval) are provided to calculate AAR-ELAs between 0.4 and 0.8 with 0.05 interval and AABR-ELAs between 0.9 and 4.4 with 0.01 interval. By providing constant AAR (rather than constant glacier area), this approach adjusted glacier geometries (area) to future ELA variations. For constant AAR of 0.4–0.45, a 90-m ELA decrease from 5769 to 5679 m of Baltoro glacier adjusted its geometries by reducing ~ 5% area. The highest decrease of 140-m ELA of the same glacier is reported for constant AAR of 0.7–0.75, revealing a significant loss of 8% geometries. The projected geometry losses for all these glaciers are highly variable, with top-heavy glaciers (Biafo and Baltoro) projected to experience the major losses in glacier-ice area. It is concluded that the quality of ELAs is highly dependent on the reconstructed three-dimensional glacier surfaces.
Highlights
Within Hindu Kush Himalaya (HKH), Karakorum Range has the highest share of the glaciated area with approximately 37% of the area under glaciation [4] with 10% being debris covered [20]
Our results suggest that a 100-m Equilibrium line altitude (ELA) (Fig. 6a) decrease will increase the number of Shigar River Basin (SRB) glaciers by 10%, while increasing glacier area by 15% and glacier volume by 12%
The difference in the ELA between area ratio (AAR) and area balance ratio (AABR) methods indicates that the AABR method is appropriate to estimate ELA of clean-ice covered and snow-fed glaciers (Pellitero et al, 2013), but we tested for debris-covered glaciers; the AABR ELA needs to be verified through field data
Summary
Within Hindu Kush Himalaya (HKH), Karakorum Range has the highest share of the glaciated area with approximately 37% of the area under glaciation [4] with 10% being debris covered [20]. Pakistan’s Karakoram region has a large variety of glacier types (e.g. avalanche nourished, snow and ice avalanches nourished, snow-fed and small-ice mass fed) [8, 9, 13, 19, 33, 34] and climatic conditions, but glacier characteristics are still only poorly known [16]. Estimation of equilibrium line altitude (ELA, the separating contour between a glacier’s accumulation and ablation area) becomes hard to accomplish because zero mass-balance (the net variation in glacier mass over a fixed year) observations of the majority of Karakoram’s glaciers are not available [35]. The rugged glacier-covered terrains and severe climatic conditions in the Karakoram lead to scarcity in field observations.
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