Rapid glacier Shrinkage and Glacial Lake Expansion of a China-Nepal Transboundary Catchment in the Central Himalayas, between 1964 and 2020

Abstract

Climate warming and concomitant glacier recession in the High Mountain Asia (HMA) have led to widespread development and expansion of glacial lakes, which reserved the freshwater resource, but also may increase risks of glacial lake outburst floods (GLOFs) or debris floods. Using 46 moderate- and high-resolution satellite images, including declassified Keyhole and Landsat missions between 1964 and 2020, we provide a comprehensive area mapping of glaciers and glacial lakes in the Tama Koshi (Rongxer) basin, a highly glacierized China-Nepal transnational catchment in the central Himalayas with high potential risks of glacier-related hazards. Results show that the 329.2 ± 1.9 km2 total area of 271 glaciers in the region has decreased by 26.2 ± 3.2 km2 in the past 56 years. During 2000–2016, remarkable ice mass loss caused the mean glacier surface elevation to decrease with a rate of −0.63 m a−1, and the mean glacier surface velocity slowed by ~25% between 1999 and 2015. The total area of glacial lakes increased by 9.2 ± 0.4 km2 (~180%) from 5.1 ± 0.1 km2 in 1964 to 14.4 ± 0.3 km2 in 2020, while ice-contacted proglacial lakes have a much higher expansion rate (~204%). Large-scale glacial lakes are developed preferentially and experienced rapid expansion on the east side of the basin, suggesting that in addition to climate warming, the glacial geomorphological characters (aspect and slope) are also key controlling factors of the lake growing process. We hypothesize that lake expansion will continue in some cases until critical local topography (i.e., steepening icefall) is reached, but the lake number may not necessarily increase. Further monitoring should be focused on eight rapidly expanding proglacial lakes due to their high potential risks of failure and relatively high lake volumes.

Glacial Lake Changes and Risk Assessment in Rongxer Watershed of China–Nepal Economic Corridor

“…We mapped a total area of glacial lakes with coverage of 13.68 km 2 in 2010 and 14.89 km 2 in 2020. The area is in accordance with another study conducted in the same watershed in 2020 that mapped glacial lakes with an area of 14.4 km 2 [18]. The number of glacial lakes increased from 215 in 1990 to 309 in 2020, representing an increase of 93 lakes.…”

“…This interaction leads to more ice mass loss, which ultimately results in the expansion of glacial lakes [61,62]. The temperature increase rate was measured at 0.01 • C a −1 from 1979 to 2019 in the Rongxer watershed [18]. In the context of increasing temperature, end-moraine-dammed lakes are expanding significantly as the primary type of GLOF events [60].…”

“…On 5 July 2016, the GLOF caused by Gongbatongsha Tsho destroyed 77 dwellings, three bridges, and one road, and it caused damage to the upper Bhotekoshi hydropower plant in Nepal, resulting in economic losses amounting to USD 70 million [14,15]. The Rongxer Watershed has recorded three GLOFs, encompassing the 1991 Chubung GLOF [16], the 1992 Upper Langbu Tsho [17], and another GLOF event in 2018 [18]. As a critical trade channel in the developmental link between China and Nepal, this basin faces threats from GLOFs.…”