Bucking the trend: Glaciers in Astore Basin have remained stable in recent times

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A recently conducted research on the glaciers in the Astore basin in the northwestern Himalaya found that they follow a similar trend to the glaciers of the Karakoram, where glaciers have remained stable since the early 21st century. The study estimated the current behaviour of glaciers in the northwestern Himalaya in situ using differential Global Positioning System (dGPS) and remote-sensing data. The study investigated Harcho Glacier’s surface elevation changes over 17 years (1999−2016).

Ground-based research results showed much lesser mass loss compared with that detected through remote sensing, with remarkably low uncertainty. The findings of the research also suggest that the glaciers significantly shrank in the 19th century in contrast to the recent stable conditions.

Astore basin in the northwestern Himalaya. The glaciers (debris-free and debris-covered) and the only climate observatory in the basin are shown here. The mass balance of the Harcho Glacier was observed in the field, whereas data for glaciers outlined in black are from Brun et al. (2017).

Harcho Glacier, a debris-covered valley, was selected as the study site to represent the behaviour of regional glaciers since a majority of them are debris-covered at lower elevations. The study also combined available historical data from a 1934 topographical map with more recent photographs taken in 1994 and a high-resolution QuickBird image from 2016 to track terminus changes. 

The study estimated the glacier surface elevation changes and found that thick debris-covered terminus exhibits slight surface elevation lowering with significant heterogeneity. However, the elevation changes vary positively from the middle to the upper (clean ice) zone of the glacier. A general negative surface elevation change characterizes the debris-covered ablation zone, whereas positive changes characterize the clean ice portions of the glacier.

Map of the glacier surface elevation change (m) between 1999 and 2016 at all measured points on Harcho Glacier. Fifty-metre elevation contour lines are overlaid on the glacier. The debris-covered part of the glacier is shown with a grey background, and the debris-free zone is in white.

The estimated results of the study regarding surface glacier loss are more negative than those derived from a similar study by Brun et al. (2017). However, the ground observations have lower uncertainty relative to those from remote sensing alone. These findings suggest that glacier mass loss in the Astore basin is slight and comparable with the adjacent Karakoram region over 17 years (1999–2016). The extensive debris coverage and the combined climate effects of the westerlies and South Asian monsoon (similar to the Karakoram glacial setting) are the most likely reasons for the limited glacier retreat in the Western Himalaya. These changes are also consistent with recent insignificant changes in temperature and precipitation records reported in the Astore basin (Muhammad and Tian 2016). 

The study improves the understanding of the current glacier mass-balance changes in the region, providing data on surface elevation change and mass balance. “Our ground observations help understand the present mass balance of glaciers with reduced uncertainty and allow for comparisons and evaluations with earlier findings,” said the lead author Sher Muhammad, Remote Sensing Specialist at ICIMOD. 

The research was carried out by ICIMOD in collaboration with researchers from the Institute of International Rivers and Eco-security, Yunnan University, China, and South Asia Institute, Heidelberg University, Germany.

Additional information
Link to the full published article: https://doi.org/10.1017/jog.2019.5
Citation for the full article:
Muhammad, S., Tian, L., & Nüsser, M. (2019). No significant mass loss in the glaciers of Astore Basin (North-Western Himalaya), between 1999 and 2016. Journal of Glaciology, 65(250), 270–278. doi:10.1017/jog.2019.5.

References
Brun, F., Berthier, E., Wagnon, P., Kääb, A. & Treichler, D. (2017). A spatially resolved estimate of High Mountain Asia glacier mass balances, 2000–2016. Nature Geosciences, 10(9), 668.

Muhammad, S., & Tian, L. (2016). Changes in the ablation zones of glaciers in the western Himalaya and the Karakoram between 1972 and 2015. Remote Sensing of Environment, 187, 505–512, https://doi.org/10.1016/j.rse.2016.10.034.