Glacier changes in the Chhombo Chhu Watershed of the Tista basin between 1975 and 2018, the Sikkim Himalaya, India

Abstract

Abstract. Glaciers of the Tista basin represent an important water source for mountain communities and a large population downstream. The article presents observable changes in the Chhombo Chhu Watershed (CCW) glacier area of the Tista basin, the Sikkim Himalaya. The CCW contains 74 glaciers (> 0.02 km2) with a mean glacier size of 0.61 km2. We determined changes in glaciers from the declassified Hexagon Keyhole-9 (KH-9) (1975), Landsat 5 Thematic Mapper (TM) (1989), Landsat 7 Enhanced Thematic Mapper Plus (ETM+) (2000), Landsat 5 TM (2010), and Sentinel-2A (2018) images. The total glacier area in 1975 was 62.6 ± 0.7 km2; and by 2018, the area had decreased to 44.8 ± 1.5 km2, an area loss of 17.9 ± 1.7 km2 (0.42 ± 0.04 km2 a−1). Clean glaciers exhibited more area loss of 11.8 ± 1.2 km2 (0.27 ± 0.03 km2 a−1) than partially debris-covered and maximally debris-covered glaciers. The area loss is 5.0 ± 0.4 km2 (0.12 ± 0.01 km2 a−1) for partially covered glaciers and 1.0 ± 0.1 km2 (−0.02 ± 0.002 km2 a−1) for maximally covered glaciers. The glacier area loss in the CCW of the Sikkim Himalaya is 0.62 ± 0.5 km2 a−1 during 2000–2010, and it is 0.77 ± 0.6 km2 a−1 during 2010–2018. Field investigations of selected glaciers and climatic records also support the glacier recession in the CCW due to a significant increase in temperature (0.25 ∘C a−1) and more or less static precipitation since 1995. The dataset is now available from the Zenodo web portal: https://doi.org/10.5281/zenodo.4457183 (Chowdhury et al., 2021).

Glacial Lake Evolution (1962–2018) and Outburst Susceptibility of Gurudongmar Lake Complex in the Tista Basin, Sikkim Himalaya (India)

“…GL-2 reached its maximum expansion rate before 1962, and now no significant changes are expected because an abrupt mountain cliff face topography bounds its upper extent. In contrast, the mother glacier of GL-3 (i.e., Gurudongmar Khangse) began to retreat significantly later [19]. This retreat is probably due to the larger accumulation area of the glacier and its greater thickness and speed.…”

“…Therefore, the glacier began to respond to climate change later. Further, the mechanism of ice-calving into the GL-3 could have been the key reason for the faster lake growth in the upper part of the glacial area after 1962 [19]. The decrease in annual precipitation, as well as decrease in the spring, summer, and autumn precipitation, was evident during 1980-1985, and constantly increasing annual average temperature (Figure 7) together with this might have stimulated the retreat of the parent glacier of GL-3.…”

“…In Sikkim Himalaya, a recent study by Chowdhury et al [19] showed that the mother glacier of GL-3 and GL-2 had an area loss of −1.1 ± 0.06% a −1 and −0.2 ± 0.05% a −1 over the period between 1975 and 2018. This inconsistent rate of glacier melting and calving processes played a dominant role in individual lake area enlargement over the years.…”

“…One of the most vulnerable areas of very fast deglaciation is Eastern Himalaya [14][15][16], where many historical GLOFs have been reported [17]. It is known that the magnitude of glacier downwasting in Sikkim is relatively faster than for other regions (i.e., Western, Central, and the Karakoram) of the entire Himalaya [18][19][20][21]. The continuous growth of numerous glacial lakes has also been reported on the north face of the Kangchengyao massif of Sikkim Himalaya between 1988 and 2014 by Debnath et al [22].…”

Long Time-Series Glacier Outlines in the Three-Rivers Headwater Region From 1986 to 2021 Based on Deep Learning

“…Glacier area uncertainty estimation is necessary to assess the significance of the results and to avoid misinterpretation of the mapping of the glacier area [51]. The potential error of glacier mapping mainly arises from positional error [52].…”