Glaciers and Water Security: Zanskar Glacier Decline and Indus Basin Risks

GS III: Conservation, environmental pollution and degradation.

Context: A recent study published in “The Cryosphere” has found that glaciers in the Zanskar region of Ladakh have slowed significantly over the past three decades. 

Key Findings of the Study

• Declining Glacier Velocity: The study found that glaciers in Zanskar slowed by an average of 2.4 metres per year per decade between 1992 and 2023.
• Accelerating Thinning: The rate of surface thinning increased from around 0.22 metres per year during 2000–2005 to approximately 0.57 metres per year during 2015–2020.
• Thinning–Slowdown Mechanism: When glaciers lose more ice than they gain, their thickness decreases. This reduces the driving stress responsible for glacier movement.

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Climate Drivers

• Western Disturbances: Zanskar receives much of its winter snowfall from Western Disturbances. Changes in their frequency, intensity, and temperature can reduce winter accumulation and worsen the negative mass balance of glaciers.
• Rising Temperatures: Increasing temperatures enhance snow and ice melt, causing sustained glacier thinning and retreat.

• Black Carbon and Dust: Deposition of black carbon and dust reduces the snow albedo, causing the surface to absorb more solar radiation and accelerating snow and ice melt, particularly at high elevations.
  • Albedo refers to the fraction of incoming solar radiation reflected by a surface.
  • Fresh snow has a high albedo, reflecting most of the Sun’s radiation and therefore absorbing less heat.

Why Do Glaciers Behave Differently?

• Glacier response is influenced by geometry, debris cover, slope, ice thickness, and terminus conditions.
• Land-Terminating Glaciers: Their flow is largely governed by ice thickness, surface slope, and basal conditions, making thinning an important factor in declining velocity.
• Lake-Terminating Glaciers: These glaciers can display different behaviour because interaction with pro-glacial lakes may reduce resistance at the terminus. 
  • Calving and reduced basal friction can cause localised acceleration, even when the broader glacier is losing mass.
    • Calving is the process in which large pieces of ice break off from the terminus of a glacier, usually into a pro-glacial lake or the ocean. 
• Thus, glacier slowdown is not uniform and cannot be attributed to warming alone.

Environmental and Disaster Risks

• Glacial Lake Formation: Retreating glaciers can leave behind depressions that fill with meltwater, creating pro-glacial lakes.
• Glacial Lake Outburst Floods: Meltwater accumulated behind unstable terminal moraines can suddenly breach the natural dam, triggering Glacial Lake Outburst Floods (GLOFs).
• Positive Feedback: As glaciers retreat, expanding pro-glacial lakes can enhance ice loss through processes such as calving, potentially accelerating glacier retreat.
• Downstream Vulnerability: Sudden floods can threaten settlements, roads, bridges, hydropower infrastructure, agriculture, and ecosystems in downstream valleys.

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Implications for the Indus Basin

• Peak Water: Increased glacier melting can initially raise river discharge, a phenomenon known as peak water. However, once glaciers lose a substantial portion of their stored ice, their contribution to river flows can decline.
• Water Security: Long-term glacier thinning could reduce the availability of summer meltwater, particularly during periods when rainfall and snowfall are limited.
• Agriculture and Hydropower: Changes in glacier-fed flows can affect irrigation, hydropower generation, and downstream ecosystems across the Indus Basin.
• Long-Term Risk: Glacier slowdown does not immediately imply water scarcity because river flows also depend on snowfall, rainfall, groundwater, and water management. However, continued ice loss indicates declining long-term water storage capacity.

Way Forward

• Strengthen Glacier Monitoring: Combine satellite remote sensing with ground-based measurements of ice thickness, mass balance, temperature, and meltwater discharge.
• Improve GLOF Preparedness: Regularly map pro-glacial lakes, assess their stability, establish early-warning systems, and strengthen downstream disaster preparedness.
• Monitor Black Carbon: Reduce black carbon emissions from transport, biomass burning, and other sources to limit their deposition on Himalayan snow and ice.
• Strengthen High-Altitude Weather Networks: Expand meteorological observations to better understand interactions between Western Disturbances, snowfall, temperature, and glacier mass balance.
• Promote Climate-Resilient Water Management: Integrate changing glacier dynamics into planning for agriculture, hydropower, drinking water, and ecosystem conservation.
• Scale Local Adaptation: Promote community-based solutions such as Ice Stupas, artificial glaciers, water harvesting, and efficient irrigation in water-stressed Himalayan settlements.

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Conclusion

The slowdown of Zanskar’s glaciers reflects the impact of climate warming, ice loss, and changing snowfall patterns on Himalayan cryospheric dynamics. While meltwater may provide short-term gains, declining glacier storage poses long-term risks to the Indus Basin, requiring stronger monitoring, GLOF preparedness, and climate-resilient water management. 

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