Pratima Pandey & G. Venkataraman
Centre of Studies in Resources Engineering,
Indian Institute of Technology, Bombay, Mumbai, India
Glaciers are the visible indicator of climate change. Glacier mass balance, length and snow-melt runoff are some of the glacier parameters directly related to the climate. Glacier length changes in response to climate change with a time delay. This paper studies the change in the length of a benchmark glacier, Chhota Shigri of the Indian Himalayan Mountains, in response to climate change. Remote sensing data and a Toposheet map of 1962 have been used to study the change in the glacier from 1962- 2008. It was found that the glacier has retreated by a length of about 950 meters from 1962 to 2008.
It is now known and accepted that the climate is changing. Glaciers are the most visible indicators of global change . Climate controls the glacier behavior and any change in climate is reflected in the glacier. The glacier study is important in the sense that it has a direct relation with climate change. Glaciers respond to change in climate in terms of glacier length, mass balance and runoff. The climate and glaciers are interrelated. Thereby, the glacier length change, the advance or retreat, is the indirect, delayed, filtered but also enhanced signal to a change in climate, whereas the glacier mass balance, or the change in thickness or volume, is the direct and undelayed response to annual atmospheric conditions . It is the climate that is the driving force controlling the mass balance of a glacier in space and time, and resulting in the recession and advancement of a glacier.
Climatic ice fluctuations cause variation in the amount of snow and ice lost by melting. Such changes in the mass balance initiate a complex series of changes in the flow of a glacier that ultimately results in a change of the position of terminus . Figure 1 is a flow chart showing the relation between glacier length and climate.
The Himalayas are the youngest and highest mountains of the world and have the largest concentration of glaciers outside the polar caps, with glacier coverage of 33,000 square kilometers  . The region is aptly called the “Water Tower of Asia” as it provides around 8.6×106 m3 of water annually . Glaciers in the Himalayas feed many important rivers of Asia including Ganga, Amu Darya, Indus, Brahmaputra, Irrawaddy, Salween, Mekong, Yangtze, Yellow, and Tarim. Apart from feeding the rivers, the Himalayas also play a significant role on the meteorological condition of India. As it is well established that the climate is changing, the same is reflected from the glacier behaviors in terms of size, health and runoff.
Temperature and precipitation are the two most important parameters to study climate change. It is established that the globe is warming. The All-India mean annual temperature has increased by 0.05 degrees Celsius every 10 years from1901-2003, and in the recent three decades, the all-India mean annual temperature has increased by 0.22 degrees Celsius every 10 years, marking a substantial acceleration of the warming trend in the recent period .
Speaking of the Himalayas, it is confirmed that the northwest Himalaya region has warmed significantly at a higher rate than the global average. A significant rise of 1.6 degrees Celsius from 1901-2002 has been reported in the northwestern Himalayas . The seasonal mean and maximum, and minimum winter temperatures from 1985 to 2008 also have increased over the Himalayas . The study also reported change in the pattern of seasonal snowfall during the winter in the western Himalayas from 1989-2007. There is a decreasing trend in the winter snowfall from 1989-2008.
Due to the rising temperature in the Himalayas, Himalayan glaciers are melting faster than in other areas of the world . There is a feedback relationship between the glacier and climate. Less snow in the winter and warmer temperatures in the summer will cause a higher equilibrium line and consequently, a negative mass balance causing the glacier to retreat in response. The mass balance of a glacier is the change in mass per unit area over a period of time. It is the difference between the amount of snow and ice accumulation on the glacier and the amount of snow and ice ablation, melting and sublimation, lost from the glacier. Accumulation includes all processes that add snow and ice to the glacier, and ablation includes all processes by which snow and ice are lost from the glacier . ELA is a theoretical snow line at which the glacier mass balance is zero.
A glacier in response to climate will either advance or retreat with a response time of its own. The glacier response time depends on the size and thickness of the glacier. Studies have been done on the Himalayan glaciers, its change in area and length, change in mass balance, glacier velocity and on the run off. These parameters reflect the climatic effect on the glacier. A geological Survey of India  studied the Gara, Gor Garang, Shaune Garang, and Nagpo Tokpo Glaciers of Satluj River Basin and observed an average retreat of 4.22 to 6.8 meters a year. A study done by Kulkarni and others for 466 glaciers located in northwest Himalayan shows those maximum glaciers of the region are in the state of retreat . The Gangotri glacier of the Himalaya has been in retreat by 2 kilometers from 1780 to 2001 and is still in a retreating state.
The present study makes an attempt to document the change in the length of Chhota Shigri glacier due to change in climate over the past years from 1962- 2008.
2. STUDY AREA
To study the effect of change in climate on glacier length, Chhota Shigri glacier was chosen, as it is located in climatically important region of the Himalayas. The glacier lies in the Chandra basin that is a sub basin of Chenab Basin and comes under Himachal Pradesh, India. The glacier is climatologically important, as it is located in the monsoon-arid transition zone. The glacier is considered to be a potential indicator of the northern limits of the intensity of the monsoon . The glacier is influenced both by the Indian summer monsoon and by western disturbances in winter. The glacier is 9 kilometers long and is located between 32°11’ – 32°17’ N and 77°30’ -77°32’ E and occupies an elevation of 4000 to 5660 m a.s.l. .
Chhota Shigri was selected as the benchmark glacier in the HKH region by the International Commission of Snow and Ice (now this is Commission of Cryospheric Science) in 2002. The glacier has been monitored and studied by many glaciologists. Continuous field mass balance measurement was carried out on the glacier by a joint team of Indian and French researchers from 2002-2007. The glacier has shown negative mass balance for last 20 years . The cumulative specific mass balance of Chhota Shigri glacier from 1986-1989 was -0.21 m.w.e. . A study on the ELA variation of the glacier has shown that the ELA has an average rate of upward shifting by 31 meters per year from 1987- 2004 .
Field investigations at the Chhota Shigri glacier done in 1988 and 2003 suggest a retreat of 800 meters from 1988- 2003 . Kumar and Dobhal have examined the fluctuation of the snout position of Chhota Shigri glacier from 1962-1989 and stated that period as one of general retreat . In their study, they reported that the glacier had been retreating for every year between 1962 and 1989, except in 1987 when it advanced about 17.5 meters. The total recession of the glacier was 195 meters with an average rate of 7.5 meters a year over 26 years .
3. RESULTS AND DISCUSSION
Due to the harsh weather and rugged terrain of the Himalayas, monitoring of glaciers is difficult by direct field methods. Remote sensing offers an efficient technique for glacier monitoring and mapping for glaciological studies. Remote sensing has the advantages of giving a synoptic view of the Earth on a regular basis and estimation of glacier extent on satellite imagery is an important aspect of glacier retreat estimation. The change in length of a glacier shows how the climate has changed in terms of temperature and precipitation. The change in the length and in area of the Chhota Shigri glacier was studied from 1962 to 2008 using various data sources, including Toposheet maps and satellite images from different sensors.
This study was done using satellite images obtained from 1999-2008 from Indian remote sensing satellite (IRS) images, images from ASTER, and a 1963 Survey of India topographic map (1:50,000 scale) of Chhota Shigri glacier. Images taken from August through September were used, as during this period the glacier is exposed. Images with cloud cover and with recent snowfall were avoided. LISS III obtains high-resolution, 23.5 meters, images of the Earth in four different wavelengths of the electromagnetic spectrum, ranging from visible to short wave infrared (0.52µm – 1.75 µm). AWiFS sensor is an improved version compared to the WiFS sensor flown in IRS-1C/1D. AWiFS operates in four spectral bands identical to LISS-III, with a spatial resolution of 56 meters. ASTER (Advanced Space borne Thermal Emission and Reflection Radiometer) is an imaging instrument flying on Terra, a satellite launched in December 1999 as part of NASA’s Earth Observing System (EOS). It obtains high-resolution, 15 to 90 square meters, images of the Earth in 14 different wavelengths of the electromagnetic spectrum, ranging from visible to thermal infrared.
All the satellite images were georeferenced using the SOI topographic map. Images were co-registered with each other and resampled to the same resolution. The boundary of the glacier was delineated using a topographic map and the area was digitized using the Geographic Information System. The glacier boundary was delineated by visual interpretations and manual techniques using GIS. False color composite made from visible and near-infrared satellite images could be used successfully to map various glacial features such as glacier boundary, accumulation area, ablation area, equilibrium line and moraine-dammed lakes .
The change in length was measured along the centerline of the glacier, also called the glacier tongue. The shrinkage in glacier was measured in terms of change in area over the studied period. From the study of satellite images and Toposheet map, it was found that the glacier has receded by a length of about 950 meters from 1962- 2008. The glacier has vacated an area of 0.19 square kilometers from 1962- 2008, with a standard deviation of 0.065046. From 1999-2008, the glacier retreated by about 190 meters.
According to the satellite images study, the glacier has retreated at a rate of 15 meters per year from 1999-2008 (Figure 3a). The average loss in glacier area from 1999-2008 was 0.0215 square kilometers, with a standard deviation of 0.0179. Figure 3b shows the trend in the change in the glacier area from 1962 -2008. There is a decreasing trend in the glacier area with r2=0.95. The glacier has been in the continuous state of retreat as studied by the remote sensing data (Figure 4).
A glacier will happily advance in a healthy climate and retreat in response to a warmer climate. We have seen from the change in the length of the Chhota Shigri glacier for 46 years, from 1962-2008, that the glacier has retreated significantly. This change in the length is due to the change in temperature and the snowfall pattern in the Himalayan region. The glacier length change study also is important for the melt and runoff modeling purpose, which again is done for the hydrological study.
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Pratima Pandey is a Ph.D. student at the Centre of Studies in Resources Engineering (CSRE), Indian Institute of Technology, Bombay.
G. Venkataraman is a professor at CSRE.