Spatio-temporal evolution of glacial lakes in the Upper Ganga basin, Central Himalayas

Abstract

The rise in annual mean temperature due to anthropogenic climate change is causing faster melting and thinning of glaciers leading to the formation of new glacial lakes and the expansion of existing ones in the Himalayan region. This exponential growth of glacial lakes increases the availability of freshwater resources and escalates the risk of future Glacial Lake Outburst Floods (GLOFs).In the present study, Glacial lake inventories for the Upper Ganga basin were generated at the sub-basin level for 1990, 2000, 2010 and 2020 using Landsat (TM and OLI) images and semi-automated methods to understand the evolution of glacial lakes, altitudinal, orientational and typology changes. We were able to map 2,554 (area: 170.15 sq. km) glacial lakes in 1990, 2,783 (area: 191.03 sq. km) in 2000, 2,834 (area: 201.44 sq. km) in 2010, and 3,118 (area: 210.87 sq. km) in 2020. Between 1990 and 2020, the total number of glacial lakes increased by 564 (22.08%) and the total area increased by 40.72 sq. km (23.93%). In the year 2020, glacial lakes were found in 31 sub-basins of the Upper Ganga basin, out of 31 sub-basins, Arun sub-basin had the maximum number of glacial lakes (n: 734 & area: 61.66 sq. km).The mean elevation of glacial lakes increased from 5,044.81 m asl (1990) to 5,052.30 m asl (2020), showing an increase of 7.49 m asl. In 2020, the majority of the glacial lakes were distributed in the elevation zone of 5,000-5,500 m asl (n:1,404 & area: 113.79 sq. km). In the upper Ganga basin, majority of the glacial lakes were south-facing (491) in 2020.End moraine-dammed (M(e)) lakes dominate among differnt types of glacial lakes. In 1990, there were 2,081 (M(e)) lakes, which increased to 2,413 in 2020, indicating towards increasing risk of future Glacial Lake Outburst Floods (GLOFs) in the Upper Ganga basin. Therefore, the present study provides vital insights into the glacial lake dynamics of the Upper Ganga basin at the sub-basin level and will help in identifying potentially dangerous glacial lakes and developing robust policies to mitigate the impact of future GLOF events.