Why in news?

A recent study has reconstructed the long-term discharge flow of the Gangotri Glacier System (GGS), the source of the upper Ganga basin feeding the Bhagirathi River in the central Himalayas.

With climate change driving faster glacier melt globally, glaciologists are closely examining how changes in Gangotri’s discharge patterns could affect water availability, river flow, and long-term sustainability of the region’s ecosystems and livelihoods.

What’s in Today’s Article?

• Composition of the Gangotri Glacier System (GGS)
• New Study on Gangotri Glacier System (GGS)
• Key Findings of the Study
• Implications of the Study on GGS

Composition of the Gangotri Glacier System (GGS)

• The GGS comprises four glaciers — Meru (7 km²), Raktavaran (30 km²), Chaturangi (75 km²), and the largest, Gangotri (140 km²).
• Together, the system spans 549 km², with about 48% glacierised area, across elevations from 3,767 m to 7,072 m.
• The GGS receives precipitation from western disturbances in winter (October–April) and the Indian summer monsoon in summer (May–September).
• Seasonal rainfall (May–October) averages 260 mm, with a mean temperature of 9.4°C recorded between 2000–2003.

New Study on Gangotri Glacier System (GGS)

• The Hindu Kush Himalaya (HKH) holds vital snow and ice reserves that feed major rivers like the Indus, Ganga, and Brahmaputra, sustaining millions of lives.
• In recent decades, climatic changes have altered the cryosphere and hydrological cycles, leading to faster glacial retreat and shifting seasonal discharge patterns.
• While most modelling studies focus on large river catchments, it is difficult to separate the impacts of snowmelt and precipitation there.
• Smaller systems like the GGS allow for more precise assessments, making it a preferred choice for hydrologists and climate scientists.
• However, long-term discharge analysis and understanding climatic drivers have remained limited.
• To address this, a new study titled “Hydrological Contributions of Snow and Glacier Melt from the Gangotri Glacier System and Their Climatic Controls Since 1980” was conducted.
• The study, published in the Journal of the Indian Society of Remote Sensing, provides deeper insights into GGS’s meltwater contributions and climate influences.

Key Findings of the Study

• The study combined the Spatial Processes in Hydrology (SPHY) glacio-hydrological model with the Indian Monsoon Data Assimilation and Analysis (IMDAA) dataset (1980–2020) to reconstruct GGS discharge trends.
  • SPHY model is a hydrological modelling tool suitable for a wide range of water resource management applications.
• It found that maximum discharge occurs in summer, peaking in July (129 m³/s).
• The mean annual discharge was estimated at 28±1.9 m³/s, primarily from snow melt (64%), followed by glacier melt (21%), rainfall-runoff (11%), and base flow (4%).
• A decadal analysis revealed a shift in discharge peaks from August to July after 1990, linked to reduced winter precipitation and enhanced early summer melting.
• The highest volumetric increase (7.8%) occurred between 1991–2000 and 2001–2010.
• While mean annual temperatures rose, there was no significant trend in precipitation or glacier melt.
• Snow melt declined due to shrinking snow cover, whereas rainfall-runoff and base flow increased.
• The analysis highlighted that summer precipitation was the main driver of annual discharge, followed by winter temperature.

Implications of the Study on GGS

• The findings highlight warming-induced hydrological changes in the Gangotri Glacier System (GGS), with increasing rainfall run-off and base flow.
• This aligns with the 25% excess rainfall observed in North India’s summer monsoon (June–August), which has caused frequent floods in Uttarakhand, Jammu, and Himachal Pradesh.
• While such events are often hastily termed “cloudbursts” without scientific evidence, climate change does raise the risk of extreme rainfall.
• The study stresses the need for sustained field monitoring and advanced modelling to improve water resource management in glacier-fed river basins, ensuring resilience against future hydrological and climatic shifts.