Glacier Change, Supraglacial Debris Expansion and Glacial Lake Evolution in the Gyirong River Basin, Central Himalayas, between 1988 and 2015

Abstract

Himalayan glacier changes in the context of global climate change have attracted worldwide attention due to their profound cryo-hydrological ramifications. However, an integrated understanding of the debris-free and debris-covered glacier evolution and its interaction with glacial lake is still lacking. Using one case study in the Gyirong River Basin located in the central Himalayas, this paper applied archival Landsat imagery and an automated mapping method to understand how glaciers and glacial lakes interactively evolved between 1988 and 2015. Our analyses identified 467 glaciers in 1988, containing 435 debris-free and 32 debris-covered glaciers, with a total area of 614.09 ± 36.69 km 2. These glaciers decreased by 16.45% in area from 1988 to 2015, with an accelerated retreat rate after 1994. Debris-free glaciers retreated faster than debris-covered glaciers. As a result of glacial downwasting, supraglacial debris coverage expanded upward by 17.79 km 2 (24.44%). Concurrent with glacial retreat, glacial lakes increased in both number (+41) and area (+54.11%). Glacier-connected lakes likely accelerated the glacial retreat via thermal energy transmission and contributed to over 15% of the area loss in their connected glaciers. On the other hand, significant glacial retreats led to disconnections from their proglacial lakes, which appeared to stabilize the lake areas. Continuous expansions in the lakes connected with debris-covered glaciers, therefore, need additional attention due to their potential outbursts. In comparison with precipitation variation, temperature increase was the primary driver of such glacier and glacial lake changes. In addition, debris coverage, size, altitude, and connectivity with glacial lakes also affected the degree of glacial changes and resulted in the spatial heterogeneity of glacial wastage across the Gyirong River Basin.

Supra-glacial debris cover changes in the Greater Caucasus from 1986 to 2014

“…Numerous authors have found similar model results in the Himalaya (e.g. Scherler et al, 2011;Rowan et al, 2015;Jiang et al, 2018). We have presented supra-glacial debris cover change over the last 30 years in the Greater Caucasus region.…”

“…Supra-glacial debris cover affects surface melt with increasing ablation in cases of thin debris cover (less than a few cm) or decreasing ablation under continuous thick debris cover (Östrem, 1959;Nicholson et al, 2018). Obtaining information about debris cover is relevant not only with respect to its impact on glacier ablation but also because it is an important part of the sediment transport system (supra-glacial, englacial and subglacial) in cold and high mountains (Kellerer-Pirklbauer, 2008), which ultimately affect the overall dynamics and mass balance of the glaciers. Several studies show an increase in debris-covered area with overall glacier shrinkage and mass loss (Deline, 2005;Stokes et al, 2007;Kirkbride and Deline;Glasser et al, 2016).…”

“…Field measurements of debris layers have practical difficulties on a large scale, and methods for estimating supra-glacial debris thickness using remote sensing and modelling remain in development (Zhang et al, 2016;Rounce et al, 2018). Several studies have also reported the role of debris cover in promoting the formation of supra-glacial lakes (Thompson et al, 2016;Jiang et al, 2018), which are directly related to glacial hazards (Benn et al, 2012). Therefore, it is necessary to take supra-glacial debris cover into account when assessing temporal change of mountain glaciers.…”

Glacial Lakes in the Nepal Himalaya: Inventory and Decadal Dynamics (1977–2017)

“…This step was necessary for the removal of misclassified polygons of glacial lakes due to shadow and also to ensure precise lake delineations. Lakes above 2450 m that were not glacial lakes were discarded by checking the nearest glacier and Google Earth visual interpretation; meanwhile, very few glacial lakes (n = 32) were found in the elevation zone of 2450-4000 m. In addition, quality assurance and quality control (QA/QC) procedures were conducted following the procedures mentioned in the previous studies [9,33]. The obtained lakes were cross-checked with previous data [1,20], historical images in Google Earth, and a base map of World Imagery (Esri, DigitalGlobe, GeoEye) to remove misclassified lakes and add a few missed lakes by manual digitization.…”

“…The Gandaki River basin has many run-of-river (ROR) glacier-fed hydropower plants under operation and construction that lie on potential GLOF pathways of high risk lakes [23,31]. In the adjacent areas of the Nepal Himalaya (in particular, Tibet, China), considerable lake formations have been reported on the Tibetan glaciers that feed into Nepalese rivers [32,33]. These glacial lakes deserve the utmost attention, as their failure poses a regional threat.…”