Among all the mountainous regions of the world, glaciers of the Himalayas constitute the largest concentration of frozen fresh water reserves outside the Polar Regions. These glaciers are unique as they are located in subtropical and high-altitude regions, predominantly of valley type and many of them are covered with debris. Snow and glaciers are vital to human beings as they provide water for our perennial river systems and play an important role controlling global climate. In addition, these glaciers are also important indicators of climate change.
Due to its geo-climatic setting, length of almost 2,400 kilometres, high altitude of its mountain ranges, proximity to Indian Ocean and sub-polar regions, the Himalayan region undergoes annually a cycle of snow precipitation and melting. In the Himalayas, the glaciers cover an area of approximately 33,000 square kilometres, which is one of the largest concentrations of glacier-stored water in the world.
Himalayan glaciers in the Indian subcontinent are broadly divided into three river basins, namely Indus, Ganga and Brahmaputra. In fact, it is the snow and glacier melt run-off from the Himalayan region which sustains the perennial flow of the Indus, the Ganga and the Brahmaputra river systems. The higher altitudes of these three major rivers situated in temperate climate receive heavy snowfall during winters.
The Indus River originates in the Tibetan plateau near Lake Mansarovar and Mount Kailash and flows westward, south of Karakoram Range and north of the Great Himalayas to Mt. Naga Parbat where it turns sharply to the south flowing through Pakistan into the Arabian Sea near Karachi after travelling for 2,880 kilometres. In India the length of Indus River is 1,114 kilometres. The Ganga originates from the Gangotri Glacier where it is known as Bhagirathi which is joined by Alaknanda at Devprayag and combined together it is called as Ganga. The total length of the river is about 2,525 kilometres. The Brahmaputra (Yalu Zangbu or Tsang po) rises in the glacier of the Kailash range, just south of the Lake Konggyu Tsho in Tibet. The Brahmaputra with a length of 2,880 kilometres ranks amongst the longest rivers of the world. It traverses its first 1,625 kilometres in Tibet, 918 kilometres in India and the remaining 337 kilometres in Bangladesh before it drains into the Bay of Bengal.
Melt water from the Himalayan glaciers forms an important source of run-off into the North Indian rivers during critical summer months. In fact, the great northern plains of India sustain on the perennial melt of snow and glaciers meeting the water requirements of agriculture, industries, domestic sector even in the months of summer when large tracts of the country go dry. Snowfall feeds glaciers of the Himalayas and almost 30–50% of annual flow of all the rivers originating from higher Himalayas comes from its melt run-off. The run-off from the Himalayan rivers supports domestic, irrigational and industrial water demand of a very large population residing in the Himalayas and the Indo-Gangetic alluvial plains. Melt water from the Himalayan region also supports generation of hydropower and sustainability of Himalayan biodiversity and environment.
However, this source of water is not permanent as glaciers shrink and expand with change in climate and they serve as a sensitive indicator to change in our climate. Therefore we need information to understand future changes in the Himalayan snow and glacier covers and its influence on stream run-off. For water resources planning and management in North-India, it is essential to study and monitor and the state of snow and glaciers and to know the sustainability of glaciers in view of changing global scenarios of climate and water security of the nation. The inaccessible terrains and the harsh climate prevailing in the Himalayas make the task of data collection extremely difficult, therefore, space-based monitoring of these resources has been found to be an extremely viable and useful alternative.
Himalayan glaciers play an important role as a sensitive indicator of climate change. There is increasing concern among the scientific community that global warming caused by increase in concentration of greenhouse gases in atmosphere can cause significant impact on the snow and glacier melt runoff in the river systems.
The importance of snow fields and glaciers of the Himalaya also lies in their interaction with the atmosphere. Albedo from snow is one of the important components of the Earth’s radiation balance. The difference in temperature between the Himalayan snow-fields and glaciers and the Indian Ocean pulls South-West monsoon towards the Indian landmass during summer. So collectively, snow-fields and glaciers govern the climate system of the Indian land mass at regional and global scales. Sensitivity of snow-fields and glaciers to variations in temperature makes them a key indicator of climate change.
In view of the importance of snow-fields and glaciers for water security of the nation and assessing climatic impact on Indian sub-continent, the extent of snow and glaciers need to be regularly mapped and monitored. Therefore, it is important to make an inventory, monitor and assess the state of snow and glaciers and to know the sustainability of glaciers in view of changing climate and to ensure water security of the nation using space-based observations, and that is being done by Indian Space Research Organisation (ISRO). Currently there are 14 operational Indian remote sensing satellites in orbit. Images obtained from these satellites are being used for making an inventory and monitoring of Himalayan glaciers and also to carry out mass balance studies.
Compared to polar or Alpine glaciers, there is very little data on Himalayan glaciers as most are located at altitudes beyond 3,700-4,300 metres and are virtually inaccessible. But studying glaciers is critical not just in terms of the environment but for the potential disastrous consequences for people living downstream. That is why the Ministry of Environment, Forest and Climate Change, Government of India has identified ‘Snow and glacier studies of the Himalayan region’ as one of the major thrust areas. Snow and glaciers of Himalayan region are difficult to study using conventional field-based methods due to rugged topography, high altitude and extreme weather conditions. However, space-based monitoring of these resources has been found to be an extremely viable and useful alternative.
Satellite remote sensing is recognised as a viable and productive tool for monitoring the health of the glaciers. Various studies recommend that monitoring the glaciers through temporal satellite data can give the status of the glacier dynamics according to time and change in climate. Satellite data, due to its synoptic view, distinct spectral properties of snow and glaciers, high temporal frequency aided by advanced digital image processing and analysis techniques, provide accurate and reliable observations.
Space Applications Centre (SAC) of ISRO has been contributing to the development of methods/techniques for extraction and dissemination of reliable and quick information from remote sensing data pertaining to snow and glaciers of the Himalayas. The Centre has been instrumental in developing remote-sensing based techniques, models and methods to generate a large amount of digital data and maps to understand the state of Himalayan snow-fields and glaciers. This work has now assumed greater significance when the nation needs to address a large number of questions about the health and state of glaciers. There is no contemporary technique which provides this information to the nation in a very short span of time and for a large number of glaciers occurring in inaccessible regions, and this is where space technology can help. Scientists of National Remote Sensing Centre of ISRO have developed a new automated snow cover estimation algorithm for analysis of satellite imagery, which can overcome several limitations faced in interpreting the images in the conventional way.
The Geological Survey of India lists 9,575 glaciers in the Indian Himalayas. Of them, 267 are over 10 square kilometres in area. In order to assess the impact of climate change on the Himalayan glaciers, India has launched an ambitious project to monitor all Himalayan glaciers above 10 square kilometres to calculate future water availability and plan for the safety of people living downstream. The ambitious project from Kashmir to Arunachal Pradesh is aimed at monitoring 267 glaciers for water availability and retreat/advance movements due to climate change.
A national project entitled, “Monitoring Snow and Glaciers of Himalayan region (Phase-II)” was taken up under National Natural Resources Management (NNRMS) Program and jointly sponsored by the Ministry of Environment, Forest and Climate Change (MoEF&CC) and Department of Space (DOS). The project has been successfully completed by Space Applications Centre, ISRO, Ahmedabad as a nodal agency along with 18 partner institutes. The ISRO study showed that there are 34,919 glaciers spread over 75,779 square kilometres in Indus, Ganga and Brahmaputra basins, covering Himalaya and Trans-Himalaya, including Karakoram region. A large geospatial database on changes in the Himalayan snow and glaciers based on space-based observations has been generated. The information generated under the project can provide accurate and reliable information on Himalayan snow cover and glaciers based on space-based observations. It can provide up-to-date information on the state of the Himalayan cryosphere and could be utilised in climate change research, snow and glacier melt runoff modelling. A Himalayan Glacier Information System (HGIS) has been developed using some of the advanced techniques of satellite data analysis for snow and glacier studies.
According to ISRO, analysis of satellite images has revealed an “alarming recession” of glaciers in the Bhilangna basin of the Garhwal Himalayas, which were mapped from Cartosat satellite images acquired in 1965 and 2014. The ISRO study found that this main glacier had receded 4,340 metres since 1965 and had fragmented into multiple valley glaciers resulting in the total loss of 10 per cent of glacier area. The Bhilangna basin is bounded by the Bhagirati group of glaciers in north and west and the Mandakini group of glaciers in east. The basin supports 33 glaciers, of which Khatling is the largest. The water melt from Khatling and its tributary glaciers in the basin contribute to the source of Bhilangna river – the southernmost tributary of the Bhagirathi. According to the scientists, “The alarming retreat and fragmentation of valley glaciers into smaller glaciers may have profound impact on the future sustainability of Himalayan glaciers and water availability.”
Study by ISRO during last four decades has revealed a loss of 0.15 square kilometres in area of the Gangotri glacier between 2007 and 2016, although according to National Institute of Hydrology, retreat of Gangotri glacier will not have drastic influence on the flow of river Ganga because the latter is not totally dependent on glaciers for its water even in the head-waters region. The percentage of snow and glacier-fed contribution progressively reduces as one moves downstream. Rainwater and sub-surface flows contribute more than 70% of the flow of river Ganga at Haridwar. An earlier study, led by ISRO, monitored 2,018 glaciers from different regions of Himalayas from 2001 to 2011 using satellite data. The study, published in Current Science in April 2014, concluded that 1,752 glaciers (86.8%) were stable, 248 (12.3%) had retreated and 18 (0.9%) had advanced. Overall the glaciers had lost about 20.94 square kilometres (0.2%) of total area. All 18 advancing glaciers were located in Karakoram Range for which no field data was available. Himalayan glaciers are being further monitored as part of a new project entitled “Integrated Studies of Himalayan Cryosphere using Space-based inputs and Impact Assessment due to Climate Change”, funded by the Department of Space.
One of the impacts of melting of glaciers is the formation of new glacial lakes by accumulation of meltwater resulting from the glacier retreat. These new lakes formed due to shrinking glaciers in the Himalaya and other mountainous regions have increased the risk of glacial lake outburst floods (GLOFs). The Hindu Kush Himalaya also has widespread presence of such glacial lakes and many of them are potential sources of flood. A number of GLOFs have occurred in the Hindu Kush Himalayas in recent years, some of which have caused considerable damage across international borders. Lives have been lost, livelihoods destroyed, and extensive damage to infrastructure has occurred.
According to Anil Kulkarni, distinguished visiting scientist at the Divecha Centre for Climate Change (DCCC) at Bengaluru’s Indian Institute of Science, who for three years has been heading a team studying the Gangotri glacier at the source of the Ganga river, investigations in Indian Himalaya suggest that most of the glaciers are retreating and also losing mass. This consistent shrinkage in mass and extent can affect stream runoff over a long term. In addition, this process can be further influenced if more glacial lakes are formed due to increase in debris cover and if black carbon (soot) is transported in accumulation areas of the glaciers. Therefore, continuous monitoring is needed to understand changing dynamics of Himalayan glaciers. He says the remote sensing method is able to check whether the glaciers are retreating or advancing and if retreating, where glacial lakes will form. He says the method they are working on will give an idea if glaciers retreat, how big a lake and exactly where (size and location both) it would form. The Divecha Model, as Kulkarni calls it, involves collecting detailed field data and is strategically important not just to know future water availability but also to plan for safety and security of people downstream. While the new programme has enthused the scientific community, environmentalists and disaster management experts say it is too soon to be useful for the people who would be directly affected, in this case, people living downstream of potential glacial lake outburst floods (GLOFs). The reason is simple. According to ISRO, all its remote sensing images of Himalayan glaciers are available online for anyone to access and interpret for application on ground. But we cannot really expect a layman from a remote hilly hamlet to access ISRO image to know if his village will be hit by floods or not. Satellite-based monitoring of Himalayan snow-fields and glaciers can nonetheless provide a means to predict any impending danger and help authorities take precautionary measures like issue advance warning and evacuating affected population from the threatened areas if necessary.