Why in News: A 2025 study by IIT Indore, U.S. universities, and ICIMOD found that the Gangotri Glacier System (GGS), which feeds the Bhagirathi river, is witnessing earlier snowmelt and shifting discharge peaks (from August to July) due to climate change, altering its hydrological cycle and increasing rainfall-runoff dependence.
Introduction
- The Gangotri Glacier System (GGS), part of the Hindu Kush Himalaya (HKH), is the primary source of the Bhagirathi river, a key tributary of the Ganga.
- Recent scientific studies highlight that climate change is accelerating glacial retreat and altering discharge patterns, with significant implications for water security, ecosystems, and disaster risks in North India.
Significance of GGS
- Covers 549 sq. km, ~48% glacierised.
- Includes Gangotri (140 km²), Chaturangi (75 km²), Raktavaran (30 km²), Meru (7 km²) glaciers.
- Receives precipitation from:
- Western Disturbances (winter, Oct–Apr)
- Indian Summer Monsoon (summer, May–Sept)
- Critical for Bhagirathi River flow and sustains agriculture, hydropower, and communities downstream in Uttarakhand and the Gangetic plains.
Key Findings of the Study
Discharge Trends
- Mean annual discharge: 28±1.9 m³/s.
- Major contribution: snowmelt (64%) > glacier melt (21%) > rainfall run-off (11%) > base flow (4%).
- Maximum discharge in July (129 m³/s), peak shifted from August → July (post-1990).
Shifts Observed (1980–2020)
- Snowmelt declined due to decreasing snow cover.
- Rainfall run-off and base flow increased → warming-induced hydrological change.
- Decadal peak rise: 7.8% increase in discharge between 1991–2000 and 2001–2010.
Climatic Drivers
- Mean annual temperature increased.
- No significant trend in annual precipitation.
- Summer precipitation is the main driver of annual discharge, followed by winter temperature.
Climate Change Impacts on the Water Cycle
- Earlier snowmelt → peak discharge advanced to July, reducing late-summer water availability.
- Reduced snow cover → decreases gradual release of meltwater.
- Increased rainfall dependence → higher variability, erratic monsoon, greater flood risk.
- Base flow rise → altered groundwater-surface water balance.
- Overall trend: From glacier-fed stability → rain-fed volatility.
Implications
Water Security
- Alters flow regimes of Bhagirathi → impacts irrigation, drinking water, and hydropower.
- Decline in snow reserves may reduce dry-season flows in future.
Disaster Risk
- Increasing rainfall-runoff linked with flash floods, cloudburst-like events, landslides.
- Uttarakhand and Himachal Pradesh witnessing frequent extreme weather events.
Hydrological Balance
- Shift from snowmelt-dominated system to rainfall-dominated → unstable seasonal supply.
- Risk of “peak water” phenomenon: initial increase due to melting, followed by long-term decline.
Ecological & Societal Impact
- Stress on riverine ecosystems.
- Livelihood risks for mountain communities.
- Greater stress on governance mechanisms for disaster management and river basin planning.
Challenges
- Data limitations: Sparse ground-based monitoring in Himalayas.
- Attribution difficulty: Distinguishing between anthropogenic climate change and natural variability.
- Policy gaps: River basin planning still monsoon-centric, not climate-adaptive.
- Community vulnerability: Local populations lack resilience strategies against erratic flows.
Way Forward
- Strengthen Monitoring: Expand glacier and hydrological monitoring (remote sensing + field stations).
- Integrated River Basin Management: Adapt water-sharing, dam operations, and agriculture planning to altered flow regimes.
- Climate Adaptation Measures: Promote water-use efficiency, crop diversification, and community-based disaster preparedness.
- Science-Policy Interface: Incorporate research findings into State and national water policies.
- International Cooperation: Collaborate under HKH regional frameworks (e.g., ICIMOD) to share data and strategies.
UPSC Relevance
GS Paper-I (Geography):
- Himalayan glaciers and their role in river systems
GS Paper-III (Environment & Disaster Management):
- Climate change and its impact on hydrological cycles
Mains Practice Question
Q. “Climate change is altering the hydrological balance of Himalayan glacier-fed rivers.”With reference to the Gangotri Glacier System, discuss the impact of shifting snowmelt and rainfall-runoff patterns on water security and disaster risks in India. Suggest measures for climate-resilient water governance. (15 marks, 250 words)