Impact of glacial retreat in Himalayas on Hydrology: A Comprehensive Review
Often referred to as the “Third Pole,” the Himalaya and Hindu Kush, are the largest concentration of glaciers outside the polar regions. Himalayan glaciers are critical of freshwater in Asia, feeding major river systems like the Indus, Ganges, Brahmaputra, etc. Supporting about 1.9 to 2 billion people. With climate change and global climate change, growing rate of glacial retreat is becoming a major issue which is leads to major issues related to water and food security, river discharge change, underground water recharge, the risk of floods and droughts across the region (Bolch et al., 2012; Kulkarni et al., 2021). This literature review examines the hydrological impacts of Himalayan glacier retreat and explores its subsequent socio-economic implications.
Glacier Retreat in the Himalayas
Rising global temperatures has accelerated Himalayan glaciers retreat over the past few decades. According to studies up to 67% of Himalayan glaciers has been lost in last decade itself, and projections predict more paid decline with current temperature rise (King et al., 2021). Some recorded examples are Gangotri Glacier has been retreat at an average rate of 18.5 meters per year from 1963 to 2006 (Ramanathan, 2011) and Samudra Tapu Glacier receded by 862 meters during the same period (Kulkarni et al., 2007). The annual rate of glacial shrinkage in the Indian Himalayan region ranges from 0.2–0.7% for 11 river basins between 1960–2004, with a mean extent of 0.32–1.4 km² (Kulkarni et al., 2011; Bolch et al., 2012).
The Himalayan glaciers are retreating at rates ranging from 10 to 60 meters per year, with many small glaciers already disappearing (Dasgupta & Sen, 2020). Satellite imagery shows the Zemu Glacier in Sikkim has significantly receded since 1935 (Singh, 2016). This trend is attributed to rising temperatures, reduced snowfall, and black carbon deposition that decreases the reflective capacity of ice, accelerating melt (Lee et al., 2021).
The rate of glacier retreat is influenced by various factors , including rising temperatures, changes in precipitation patterns, and the deposition of black carbon, which reduces the albedo effect and accelerates melting. The rate of glacier retreat is not uniform across the Himalayas; it varies due to regional climatic conditions, glacier size, and topographical features. Research shows that smaller glaciers are retreating faster compared to larger ones due to their lower ice mass and surface area (Bolch et al., 2012).
Hydrological Impacts
1. Variation in River Runoff
Glacier melts significantly impact on the rivers water discharge originating from the Himalayas. Major rivers like Indus, Ganges, Brahmaputra etc are glacier-fed water, especially during dry seasons. Glacier retreat initially cause increase in river discharge due to accelerated melting, which raises the risk of floods and soil erosion (Immerzeel et al., 2010). But, with continued glacial retreat, there is reduction in river flow due to decreased discharge which leads to water availability for agriculture, drinking, and industrial use (Prakash, 2020).
Studies predict that the upper catchments of these rivers will experience an initial increase in streamflow due to accelerated melting, followed by a sharp decline as glacial storage is exhausted (Singh et al., 2013). For instance, the Indus Basin, heavily reliant on glacial melt, may see its water availability significantly impacted by mid-century (Lutz et al., 2014).
Seasonal variations in runoff patterns are also becoming more pronounced. The shift from glacial to rainfall-dominated river systems can result in more erratic flow regimes, increasing the frequency of both floods and droughts. This has significant implications for water resource management, particularly in regions that depend on consistent river flows for irrigation and hydropower (Immerzeel et al., 2010).
2. Variability in Seasonal Flow
Observed shift in period of peak flow from glacier to earlier period of the year , which was originally observed during summer months (Rasul & Molden, 2019). This has lead to decreased water availability during critical agricultural periods, affecting crop irrigation and also affects hydropower generation, during summers which is period of high energy demand (Pathak et al., 2017).
This shift in seasonal flow patterns can lead to mismatches between water supply and agricultural demand. For example, earlier peak flows may coincide with periods when water demand for irrigation is low, while reduced flows during the actual growing season can negatively impact crop yields. Moreover, changes in flow timing affect aquatic ecosystems, disrupting the life cycles of fish and other aquatic organisms dependent on specific flow conditions (Pathak et al., 2017).
3. Groundwater Recharge
Initial increase in river runoff assist in groundwater recharge especially during dry months , (Kulkarni et al., 2007). But as glaciers retreat, there is reduction in meltwater flow which leads to declining groundwater levels (Rasul & Molden, 2019). When this situation persists for long period it far reaching impacts.
Groundwater systems are particularly vulnerable to changes in glacial meltwater input. In many Himalayan regions, groundwater serves as a critical buffer against seasonal water shortages. The decline in recharge rates due to reduced meltwater can lead to the over-extraction of groundwater resources, exacerbating water scarcity issues. Additionally, changes in groundwater recharge can affect water quality, as lower recharge rates reduce the dilution of pollutants (Rasul & Molden, 2019).
4. Glacial Lake Outburst Floods (GLOFs)
Glacial lakes which are formed due loose moraine or ice left by glacier retreat that are highly vulnerable to sudden breaches, causing catastrophic Glacial Lake Outburst Floods (GLOFs) (Mool et al., 2001). GLOFs can lead to widespread flooding, causing the destruction on large scale. More than 32 GLOF events have been recorded in the Himalayas, with increasing frequency in recent years. (Dasgupta & Sen, 2020)
5.Floods and Droughts
During period of initial glacier retreat due to high river discharge, risk of seasonal flooding increases particularly during monsoons (Immerzeel et al., 2010). But as glaciers continue to shrink, the long-term reduction in meltwater will lead to water scarcity and an increased risk of drought, particularly affecting agriculture and drinking water supplies (Prakash, 2020).
5. Sediment Transport and River Morphology
Glacier retreat also changes the sediment transport dynamics. Initially, increased meltwater flow raises sediment loads, leading to riverbed aggradation and flood risks. Over time, reduced sediment supply can cause river incision, affecting aquatic habitats and infrastructure stability (Singh et al., 2013).
Sediment transport plays a crucial role in shaping riverine landscapes and maintaining the ecological health of river systems. Changes in sediment load can alter river channels, increase erosion rates, and impact the stability of infrastructure such as bridges and dams. Moreover, sediment deposition in reservoirs can reduce their storage capacity, affecting hydropower generation and water supply for irrigation (Biemans et al., 2019).
Socio-Economic Impacts
Hydrological changes due to glacier retreat have far-reaching socio-economic impacts, impacting agriculture, energy production, livelihoods, and public health. These impacts are interconnected, creating complex challenges for communities and governments across the Himalayan region and downstream areas.
1. Agricultural Productivity: Reduced water availability affects irrigation, leading to lower crop yields and food insecurity (Easterling et al., 2007; Rasul & Molden, 2019). Climate change-induced water stress can exacerbate existing vulnerabilities in agricultural systems, particularly in regions that rely on subsistence farming. The shifting of seasonal water availability disrupts traditional cropping patterns, leading to reduced agricultural productivity. Farmers face increased risks of crop failures, especially in regions dependent on glacier-fed irrigation systems. This situation forces many to adopt costly water management technologies or shift to less water-intensive crops, often at the expense of food diversity and nutrition (Immerzeel et al., 2010).
2. Hydropower Generation: Fluctuations in river flow impact hydropower production, affecting energy security (Biemans et al., 2019). Inconsistent water flow can reduce the efficiency of hydropower plants and increase the costs associated with energy production. The unpredictability of water discharge also complicates long-term planning for energy infrastructure, posing challenges for countries that rely heavily on hydropower as a renewable energy source. For example, Nepal and Bhutan face potential revenue losses from hydropower exports due to fluctuating water availability (Rounce et al., 2020).
3. Migration and Livelihoods: Water scarcity and agricultural decline drive migration, altering demographic patterns (Rasul & Molden, 2019). Rural communities are particularly vulnerable, as they often lack the resources to adapt to changing environmental conditions. Loss of traditional livelihoods in agriculture, animal husbandry, and related sectors forces people to migrate to urban areas in search of employment, leading to urban overcrowding and socio-economic tensions. This form of climate-induced migration disrupts community structures, erodes cultural heritage, and places additional stress on urban infrastructure and services (King et al., 2021).
4.Public Health: Changes in water availability and quality have direct and indirect impacts on public health (Dasgupta & Sen, 2020). Reduced freshwater supply can lead to poor sanitation and hygiene, increasing the risk of waterborne diseases such as cholera and dysentery. Additionally, the stress associated with displacement, livelihood loss, and environmental degradation contributes to mental health issues, which are often overlooked in disaster response frameworks.
5.Economic Stability: The economic costs of glacier retreat are substantial (Biemans et al., 2019; Wester et al., 2019). Infrastructure damage from floods, landslides, and GLOFs leads to significant repair and recovery expenses. Declines in agricultural productivity and hydropower generation reduce national GDPs, especially in countries where these sectors form the economic backbone. Furthermore, increased investment in climate adaptation measures and disaster risk reduction places additional financial burdens on governments (Rasul & Molden, 2019).
6.Biodiversity and Ecosystem Services: Changes in hydrology affect not only human systems but also natural ecosystems (Singh et al., 2013). Altered river flows impact freshwater biodiversity, disrupt aquatic habitats, and reduce the availability of ecosystem services such as clean water, fisheries, and flood regulation. These ecological changes can have cascading effects on local economies that depend on natural resources for livelihoods (Mool et al., 2001).
Conclusion
Himalayan glacier retreat poses significant hydrological which lead to numerous socio-economic and ecological challenges. Addressing these issues requires integrated water resource management, climate adaptation strategies, Disaster Risk Reduction (DRR), Sustainable Agricultural Practices and regional cooperation.
