CLIMATE SHIFT ALTERS GANGA HEADWATERS

A new study spanning four decades shows the Gangotri Glacier System — source of the Bhagirathi, a Ganga headstream — is undergoing major climate-driven shifts. Snowmelt’s share of river flow is declining, while rainfall-runoff is rising. Peak discharge has advanced from August to July, disrupting flow seasonality. Scientists warn these changes could hit irrigation and hydropower at high elevations

- S V KRISHNA CHAITANYA @Chennai

IN the icy heights of the central Himalaya, the Gangotri Glacier System (GGS) has for centuries fed the Bhagirathi, the headstream of the Ganga, India’s most iconic and culturally revered river. Now, new research shows how climate change is quietly but profoundly reshaping the flow of meltwater that sustains the river at its source — with consequences that could ripple far downstream.

A team of researchers from the Indian Institute of Technology Indore and partner institutions has reconstructed four decades of discharge from the GGS, offering the clearest picture yet of how snow, glacier ice, rainfall, and groundwater each contribute to the river’s flow, and how these proportions have shifted under a warming climate.

Published in the Journal of the Indian Society of Remote Sensing, the study deployed the high-resolution Spatial Processes in Hydrology (SPHY) model, calibrated with rare field discharge measurements (2000-2003), satellite-derived glacier mass balance data (2000-2019), and MODIS snow cover maps (2002-2020). The result is a 41-year hydrological reconstruction — the longest and most detailed yet for the Gangotri catchment.

The analysis found that snowmelt is the dominant contributor, supplying 64 per cent of annual flow, followed by glacier melt (21%), rainfall-runoff (11%), and baseflow (4%). On average, the glacier system discharges 28 cubic metres of water every second into the Bhagirathi.