Syllabus: GS-III & V– Climate change 

Why in the News?

The Himalayan cryosphere is changing rapidly under the influence of global warming. Glacier retreat is creating and enlarging glacial lakes, while unstable ice and moraine dams increase the possibility of Glacial Lake Outburst Floods.

This creates a difficult policy challenge for India: the same glacier-fed rivers that support hydropower and water security are becoming sources of new climate-related risks.

The 2023 South Lhonak Lake disaster in Sikkim, which caused extensive damage in the Teesta valley and destroyed the 1,200-megawatt Teesta-III hydropower project at Chungthang, demonstrated how a high-altitude event can cascade into major infrastructure and economic losses.

Why are Glaciers Important for Hydropower?

The Himalayas act as a major water tower of Asia. Snow and glacier melt contribute to river flows that support agriculture, ecosystems and hydropower generation.

Hydropower is also an important component of India’s clean-energy transition because it provides renewable electricity and can support grid balancing.

However, climate change is changing the risk equation.

• Glacier retreat can alter the seasonal timing and volume of river flows.
• Newly formed or expanding glacial lakes can become potential sources of sudden floods.
• Avalanches, landslides and earthquakes can trigger lake outbursts.
• GLOFs can carry enormous quantities of water, boulders, ice and sediment, damaging dams, tunnels, bridges and powerhouses.

Therefore, hydropower planning cannot depend only on conventional flood estimates.

The 2023 South Lhonak GLOF: A Warning

• In October 2023, a large section of the lateral moraine at South Lhonak Lake collapsed into the lake. 
  • The resulting displacement of water breached the moraine dam and generated a powerful flood and around 50 million cubic metres of water were released downstream. 
• The event devastated parts of the Teesta valley and caused the failure of the 1,200-megawatt Teesta-III Hydroelectric Project.
• The lesson was clear: infrastructure designed mainly for conventional river floods may remain vulnerable to high-altitude cascading hazards.

Why Arunachal Pradesh Needs Special Attention

• Arunachal Pradesh combines three important features: rapidly changing Himalayan landscapes, high hydropower potential & seismic vulnerability.
• Recent assessments have identified around 197 expanding glacial lakes in the State. 
• The National Disaster Management Authority has identified 27 high-risk lakes across five districts: 
  • Dibang Valley – 16 lakes, Tawang – 6 lakes, Anjaw – 3 lakes, Kurung Kumey – 1 lake, Shi Yomi – 1 lake.
• Satellite observations indicate significant expansion in several lakes. 
  • For instance, Sanhapo Lake in the Mago Chu basin of Tawang reportedly expanded from about 55.9 hectares to nearly 88.8 hectares between 2016 and 2026.
• This does not mean that every expanding lake will produce a GLOF. It means that risk assessment and continuous monitoring are necessary before major hazards develop.

Arunachal Is Not Simply Another Sikkim

GLOF risk is site-specific. Many potentially hazardous lakes in the Siang, Subansiri, Dibang and Lohit systems are located far upstream, including areas beyond India. Longer travel distances and intervening reservoirs may reduce flood peaks in some situations. However, this is risk reduction, not risk elimination. The final impact depends on factors such as:

• Lake volume and rate of expansion.
• Breach size and speed.
• Sediment and debris carried by the flood.
• Reservoir storage available at the time.
• Spillway and dam design.
• Location of downstream settlements and infrastructure.

Hence, the same type of hazard can produce very different outcomes in different river basins.

The Hydropower Question

Projects such as the Upper Dibang Multipurpose Project and the proposed Etalin Hydroelectric Project have raised concerns relating to seismicity, slope stability, biodiversity and cumulative environmental risks.

• The policy question is not simply “hydropower or no hydropower.” The more important question is whether projects are planned according to the latest climate and cryospheric risk assessments. Every major project in the Eastern Himalayas should therefore assess:
  • GLOF risk and changing glacial-lake behaviour.
  • Earthquake-triggered landslides and lake outbursts.
  • Sediment-heavy flood flows.
  • Cumulative impacts of multiple dams in one river basin.
  • Downstream effects on communities and ecosystems.

What Is India Doing?

The National Disaster Management Authority has developed guidelines for the management of GLOFs, focusing on risk assessment, monitoring, early warning, preparedness and mitigation. 

Government agencies and State authorities are increasingly using:

• Remote sensing and satellite monitoring to identify changing lakes.
• Automatic weather stations and real-time sensors for high-altitude monitoring.
• Early-warning systems to alert downstream communities.
• Hydrodynamic modelling to estimate possible flood pathways.
• Engineering options such as controlled lake lowering and siphoning where technically and environmentally feasible.

The National Disaster Management Act, 2005 provides the broader institutional framework for disaster preparedness, mitigation and response.

What Should Future Hydropower Planning Look Like?

The traditional approach of designing infrastructure mainly around historical rainfall and river-flow records is becoming inadequate.

Future planning should use climate projections and dynamic hazard assessments.

• Hydropower projects should incorporate GLOF-specific design standards, including debris and sediment-loaded flood scenarios.
• Reservoir operating rules should include GLOF contingencies and sufficient emergency preparedness.
• Downstream villages should have clearly identified evacuation routes, shelters and community-based warning systems.
• Environmental impact assessments should examine cumulative basin-level risks, rather than assessing every project in isolation.
• Since many hazardous lakes are located in transboundary Himalayan basins, scientific data sharing and disaster communication with neighbouring countries are essential.

The Larger Development Lesson

The relationship between glaciers and hydropower is reciprocal.

Glacier-fed rivers provide the water that makes hydropower possible, while replacing fossil-fuel electricity with low-carbon energy can contribute to climate mitigation.

But a clean-energy project is not automatically a climate-resilient project.

For the Eastern Himalayas, sustainable development means combining energy security, ecological security and disaster resilience.

Exam Hook: Key Takeaway

The Himalayan hydropower challenge is no longer only about generating clean electricity; it is about ensuring that climate-induced cryospheric hazards are built into the planning, design and operation of infrastructure.

Mains Question

“Climate change is altering the risk landscape of Himalayan hydropower.” Discuss with reference to Glacial Lake Outburst Floods in the Eastern Himalayas.

One-line wrap: India’s Himalayan energy transition can remain sustainable only when hydropower development moves together with glacier monitoring, GLOF preparedness, seismic safety and ecosystem resilience.