64% of Gangotri Glacier's discharge into Ganga in form of snowmelt: Study

NEw new delhi: well-nigh 64 per cent of the muster out from the Gangotri Glacier -- which feeds the Ganga river -- comes from the melting of fallen snowfall, patch 21 per cent comes from the melting of glaciers, researchers from the Indian Institute of Technology, Indore, have found.Eleven per cent of the discharge from the glacier system in Uttarakhand in the Hindu Kush Himalayas was linked with rainfall runoff.The team, which also included scientists from US universities and the International Centre for Integrated Mountain Development in Nepal, found that the highest discharge over a decade of about 29 cubic metres per second was seen during 2001-2010, which corresponded with the highest decadal temperature of 3.4 degrees Celsius across the study period of 1980-2020.Findings published in the Journal of the Indian Society of Remote Sensing also reveal a shift in the peak of discharge -- driven by climate change -- from August to July post-1990, which the researchers attributed to a lowered snowfall during winter and higher melting in early summer."Over the last four decades, the composition of flow from the (Gangotri Glacier System) is changing due to climate change, and this study offers the most detailed picture yet of how those changes have unfolded," says lead author Parul Vinze, a PhD scholar at IIT Indore's glaci-hydro-climate lab.Though water formed by the melting of fallen snow -- or 'snowmelt' -- dominates the flow from the Gangotri Glacier, over time, its contribution has fallen, while that from run-off due to rainfall has increased, subtly reshaping the river basin's hydrological balance, the researchers add.The study modelled and analysed 41 years of data of discharge from the glacier system to understand the decade-wise shift in patterns.The researchers found that the contribution from snowmelt in August significantly decreased from 70 per cent during 1980-1990 to 54 per cent during 1991-2000 and 41 per cent in 2001-2010, followed by an increase to 57 per cent during 2011-2020.The fall in contribution during August "occurred because of the increased early summer temperature and reduced winter precipitation from 1980-1990 to 2001-2010", the authors said."The findings indicate that snowmelt is the dominant contributor to (Gangotri Glacier System) discharge, accounting for 64 per cent of the mean annual (Gangotri Glacier System) discharge (of up to 30 cubic metres per second). Glacier melt contributed 21 per cent, while rainfall-runoff and baseflow contributed 11 per cent and four per cent, respectively," the authors wrote.The findings improve upon those from previous studies, which were limited by "shorter records, coarser-resolution climate data, or fewer calibration datasets", and provide a "more detailed analysis" than was previously possible, the team said.The study also stresses the need for continued monitoring on the field and modelling efforts to improve water resource management in glacier-fed river basins, they said.