GANGOTRI GLACIER SYSTEM (GGS)
1. Context
A recent study has reconstructed the long-term discharge flow of the Gangotri Glacier System (GGS), the source of the upper Ganga basin which contributes to the waters of the Bhagirathi river in the central Himalayas. In the wake of climate change, glaciologists the world over have been studying the impact of glacier melt.
2. Gangotri Glacier System (GGS)
- The Gangotri Glacier System (GGS) is one of the largest glacier systems in the Himalayas and holds immense significance both geographically and culturally. Stretching nearly 30 kilometers in length, it serves as the primary source of the river Bhagirathi, which later merges with the Alaknanda at Devprayag to form the Ganga, a river deeply revered in Indian civilization.
- Located in Uttarkashi district of Uttarakhand, the glacier lies in the Garhwal Himalayas at an altitude ranging from about 7,100 meters at its highest peaks to 4,000 meters at its snout, known as Gomukh, which literally means “cow’s mouth” due to its distinct shape. The glacier system is fed by several tributary glaciers such as Raktvarn, Chaturangi, and Kirti, which together form the vast Gangotri Glacier complex.
- Like other Himalayan glaciers, the GGS is highly sensitive to climatic conditions. Over the decades, it has been retreating at a significant rate, largely due to rising global temperatures and local anthropogenic pressures.
- This retreat is a matter of concern because the glacier not only sustains perennial river systems but also supports millions of people who depend on the waters of the Ganga for agriculture, drinking water, and hydroelectric power.
- Apart from its hydrological importance, the Gangotri Glacier holds a sacred place in Indian culture and mythology. It is considered the mythological abode where the Ganga descended to Earth, sanctified by Lord Shiva, before flowing across the plains. Thus, it is both a lifeline and a spiritual symbol for the people of India
3. Significance of Gangotri Glacier System (GGS)
- The snow and ice reserves of the Hindu Kush Himalaya (HKH) play a vital role in feeding major river systems such as the Indus, Ganga, and Brahmaputra. In recent decades, however, the region has witnessed significant climatic variations that have reshaped the cryosphere and disrupted the hydrological cycle.
- These changes have altered the functioning of glacier-fed river systems, leading to faster glacial retreat and shifts in seasonal water discharge.
- To understand these impacts, researchers often rely on modelling studies, which provide theoretical assessments of changing hydrological patterns. Yet, due to the vast size of these river basins, it is difficult to accurately measure river flow and separate the contributions of snowmelt from that of rainfall.
- Smaller glacier systems, like the Gangotri Glacier System (GGS), offer a more manageable scale for such assessments, making them a preferred subject of study among hydrologists and climate scientists.
- In this context, a recent study titled “Hydrological Contributions of Snow and Glacier Melt from the Gangotri Glacier System and Their Climatic Controls Since 1980” seeks to address this knowledge gap.
- Conducted by researchers from the Indian Institute of Technology, Indore, the Universities of Utah and Dayton (U.S.), and the International Centre for Integrated Mountain Development (ICIMOD), Kathmandu, the study has been published in the Journal of the Indian Society of Remote Sensing
4. Findings of the Study
- The study reconstructed the long-term discharge patterns of the Gangotri Glacier System (GGS) using a high-resolution glacio-hydrological model known as Spatial Processes in Hydrology (SPHY).
- This model simulates various components of the terrestrial water balance, including rainfall-runoff, evapotranspiration, and cryospheric processes. To enhance accuracy, it was combined with the Indian Monsoon Data Assimilation and Analysis (IMDAA) dataset covering the period from 1980 to 2020.
- The results revealed that the GGS records its maximum discharge during the summer season, with a peak flow in July reaching about 129 cubic metres per second. On average, the annual discharge over the four decades was calculated at 28±1.9 m³/s, with snowmelt making the largest contribution (64%), followed by glacier melt (21%), rainfall-runoff (11%), and base flow (4%).
- A decade-wise examination highlighted a shift in the discharge peak from August to July after the 1990s, a change linked to reduced winter precipitation and increased early summer melting.
- Further, the mean decadal discharge indicated the sharpest rise—about 7.8%—between the periods 1991–2000 and 2001–2010. While the data reflected a steady rise in mean annual temperatures, there was no significant long-term trend in either annual precipitation or glacier melt.
- Interestingly, snowmelt contributions declined despite warming, primarily due to a reduction in the average snow cover area. In contrast, both rainfall-runoff and base flow showed an increasing pattern from 1980 to 2020.
- Statistical correlations from the study suggested that the mean annual discharge of GGS is primarily influenced by summer precipitation, with winter temperature being the secondary factor
5. Other important glaciers in the Himalayas
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- The Himalayas, often called the “Third Pole,” are home to thousands of glaciers that act as crucial freshwater reserves, feeding some of the largest river systems of South Asia.
- These glaciers not only sustain perennial rivers such as the Ganga, Indus, and Brahmaputra but also serve as important indicators of climate change because of their sensitivity to temperature and precipitation variations.
- Apart from the Gangotri Glacier System, several other glaciers hold immense geographical, hydrological, and cultural importance. The Siachen Glacier, located in the eastern Karakoram range, is the second-longest glacier outside the polar regions, stretching about 76 kilometers.
- It is strategically significant as it lies near the India-Pakistan-China tri-junction, making it one of the most militarized zones in the world.
- Another important glacier is the Baltoro Glacier, also situated in the Karakoram. It is famous for being surrounded by some of the highest peaks of the world, including K2. To the west, the Biafo Glacier connects with the Hispar Glacier, forming one of the longest glacial systems outside the poles.
- In the central Himalayas, the Pindari Glacier in Uttarakhand is a well-known source of the Pindar River and is popular among trekkers. The Milam Glacier, also in Uttarakhand, is another major glacier feeding the Gori Ganga River. The Zemu Glacier in Sikkim, lying on the eastern Himalayas, is the largest glacier in the region and contributes significantly to the Teesta River.
- In the Kashmir Himalayas, glaciers like the Kolhoi Glacier in Lidder Valley and the Drang-Drung Glacier in the Zanskar region are vital for local river systems. The Dokriani Glacier near Gangotri is often used by scientists as a benchmark glacier to study retreat and climatic effects in the Garhwal Himalayas.
- Collectively, these glaciers form the backbone of water security in the Indian subcontinent, regulating river flow, supporting agriculture, hydropower, and drinking water needs for millions of people downstream.
- However, many of them are retreating rapidly due to global warming, making their conservation and continuous monitoring a pressing environmental concern
6. Way Forward
The Gangotri Glacier System (GGS) has shown a rising trend in rainfall-runoff and base flow, pointing towards hydrological changes linked to warming conditions. This year, the summer monsoon in northern India has been unusually intense, recording about 25% higher rainfall than the seasonal average between June and August. The region has witnessed several severe flooding events in Uttarakhand, Jammu, and Himachal Pradesh, which local authorities frequently describe as ‘cloudbursts.’ However, such labels are often made without scientific evidence, since neither ground-based instruments nor satellite data are available to confirm them. By definition, a cloudburst refers to an extreme weather event where more than 10 cm of rainfall occurs within an hour over an area smaller than 30 square kilometers
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For Prelims: Gangotri Glacier System, Siachen Glacier, Indian Monsoon Data Assimilation and Analysis (IMDAA)
For Mains: GS I - Geography
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Source: The Hindu
