Glacier Retreat in Doda Valley, Zanskar Basin, Jammu & Kashmir, India

Glacier monitoring is important to provide estimates of freshwater storage in Himalayan region. Therefore, understanding the spatio-temporal glacier retreat is important for utilization of the Himalayan water resource. The study area covers Dodavalley, Zanskar basin in Jammu & Kashmir. An attempt is also made here to analyze the glacier retreat and morphometric parameters like, length, width, area, area accumulation ratio (AAR), specific mass balance etc., of the glaciers using multi-temporal satellite data of IRS-1C LISS III of August 2001, Landsat of 1975, 1992 and 2002and in conjunction with Survey of India (SOI) topographical map of 1962 and United State of Geological Survey (USGS) map of 1925. In this study, it was found that, total glacier area loss from 1962 to 2001 is 18.16%. Though in the years 1975 and 1992, there is positive specific mass balance but in the year 2001, specific mass balance of all glaciers was negative.


Introduction
The Himalaya, the youngest and fragile mountain system of the earth, has direct influence on climate control, regional hydrology and environment of our subcontinent. About 17% of its mountain area is covered by glaciers (Dobhal et al., 1999). Fresh water resources in the Himalayas are stored in the form of glaciers. Change in climate directly affects glacier mass and thereby, the water resources. Melting from snow bound areas during the summer forms an important source of many perennial rivers originating in the higher Himalaya. Most of the glaciers in the mountain region of the Himalayas have receded subsequently during the last century, in response to climatic warming. Recent studies have shown wide-scale retreat of glaciers not only in the Himalayas but also in Alps, Andes and Rocky mountains (Kulkarni et al., 2002). Investigation carried out in the Himalaya suggests that almost all glaciers are retreating and annual rate of retreat is varying from 16 to 35m (Dobhal et al., 1999). Optical multispectral space borne imaging represents a well-established satellite remote sensing method for mapping and monitoring glaciers and their retreat. Remote sensing techniques using satellite optical stereo data combined with multispectral images would enable the computation of accurate DTMs for glacier morphometric characterization (Bahuguna et al., 2003). Morphometric analysis of the glaciers is an essential requirement to evaluate the nature of changes in glacier dimensions and also to establish relationship between climatic change and dynamics of glaciers (Kulkarni et al., 2002). In the Indian Himalaya, glaciers cover approximately 23,000 sq km of area and have one of the largest concentrations of glacier-stored water outside the Polar Regions. Change in climate directly affects glacier mass and thereby, the water resources. Melting from snow-bound areas during summers forms an important source of water for many perennial rivers originating in the higher Himalaya (Dobhal et al., 1999). Further, acceleration in worldwide glacier mass loss over the last few decades has significant implications in terms of global sea level rise. The glacial terrain being very difficult to have access to and limitations of conventional methods of mapping, remote sensing data plays a crucial role in glacial domain mapping (Praveen et. al, 2009). Optical range bands give good registrations of glaciers in remote sensing data.
In the present study authors attempted to analyze glacier retreat over 13 selected glaciers and its morphometric characteristics in the Doda valley of part of Zanskar basin based on multi temporal satellite data acquired during the years 1975, 1992, and 2001 and topographical maps of the years 1925 and 1962. Similar such studies on glaciers using remote sensing data were carried out by Dozier and Hall (1987) using remote sensing data. In Indian Himalayas Kulkarni et al., (2002Kulkarni et al., ( & 2005 carried out studies using remote sensing data on various aspects of glacial retreat.  Figure 1). Its elevation ranges from 3071-6401 m above msl. The highest relief areas are located in the south western parts where as the lowest relief areas are found in north eastern parts of the Doda valley. In the winters starting from mid-October and usually continuing till May, almost all parts of the valley are covered with a thick layer of snow. Throughout winter the temperature is around -20° centigrade in Zanskar valley. The summer season begins in May and it becomes warm fairly quickly. The summer season lasts relatively longer till August than in other parts of Ladakh. No tree covers exist on mountainous slope although good crop flourish in the wide valley of Padam area during summer season. In geological terms, the Doda valley is a young land, formed only a few million years ago by the buckling and folding of the earth's crust as the Indian sub-continent pushed with irresistible force against the immovable mass of Asia.In the study area various geological formations are well exposed due to no vegetation cover of the rock formations. The meta sedimentary formation exhibit well developed bedding planes, folding and faulting.

Study Area
The study area is a part of higher Himalayan Mountains and possesses a variety of slopes ranging from very gentle to steep slopes. The development of slopes largely depends on the rock composition, structure and the geomorphic processes operating in the region. The general slope of the study area is from northeast to southwest. Slope within all the glaciers of the study area generally range between 5°-15°. Doda and Zanskar are the main rivers in the study area. The direction of flow of Doda river is from northwest to southeast and it confluence with Zanskar river in south-eastern part of the study area at Padam. In the present study 13 glaciers in the Doda valley having distinct accumulation and ablation zones with well delineated boundaries in all the satellite images were taken up for studying the spatio-temporal retreat of glacier. Initially, boundaries of various glaciers were mapped using topographical map from Survey of India and subsequently by using satellite images of different time periods covering the area.

Data Source & Methodology
The oldest information about extent of the glaciers in the study area is extracted from USGS topographical map of 1925.The digital elevation model was generated using SRTM data. The generation of digital terrain model (DTMs) by draping false color composite over DEM helped in visualizing glacial processes and in glacier mapping from ablation to accumulation zones ( Figure 2). Band ratioing using Normalized Difference Snow Index (NDSI) and ratio of TM 4 / TM 5 bands was used to delineate glacier area on Landsat TM. The ratio TM-4/TM-5 effectively separate ice and snow zones over glacier surfaces, particularly in areas containing shadow (Dozier et al. 1987) and to enhance contrast in the snow zones (Paul, F., 1999). Normalized Difference Snow Index (NDSI) was effective in distinguishing snow from similarly bright soil and rock, as well as from clouds in TM imagery (Dozier et al., 1987). Flowchart of methodology is shown in the figure 3.     Table 2. It was found that due to shrinkage in glacier area few glaciers have been fragmented from its tributary glaciers. This has resulted in reduction in the total glacier extent but conversely increases in the number of glaciers.

Changes in the Snout Elevation
Change in the snout elevation reflects the dynamic processes operating in the snout region of the glacier ( (Table.3).

Retreat of Glacier Snout
On satellite images position of snout could be delineated by identifying geomorphic features such as origin of stream from the snout and disposition of end moraines (Kulkarni et al. 2005).SRTM DEM is highly useful in glacier morphometric analysis and evaluating vertical shift in the snout location. Elevation of the each glaciers snouts position during 2001 measured using SRTM DEM derived contours are also given in table 4. These glacier snouts are mainly located at more than 4000m above mean sea level. The contour data can also be used for slope and aspect calculation for evaluating terrain morphologic control on glacier retreat.

Morphometry of Glaciers
Several morphometric parameters including length, width, area, perimeter, orientation etc. were estimated directly. Glacial accumulation area was measured with respect to snow-line altitude. Snow-line altitude was obtained by measuring the distance between the ablation area (where snow-melting is the dominant process) and the accumulation area.
Another important parameter called Area Accumulation Ratio (AAR) is a ratio between accumulation area and total glacial area. Specific mass balance is computed using AAR.
In fact, the glacier and snow/ice covered area of the total study area has been divided into 147 glaciers/polygons. The glacier and snow/ice covered area in the total study area has where 'b' is the specific mass balance in water equivalent (cm) and 'X' the AAR.
The individual morphometric characteristics of the 13 selected glaciers of three time periods of satellite data are presented in Table 5 and a look into the parameters reveal that there are minor to major changes in the linear, areal and volume characteristics of all the glaciers in the study area from 1962 to 2001. Most of the glacier snouts are mainly located at more than 4000m above msl. There is general recession of snouts of all the 13 glaciers to various distances. The advancing and retreating snout positions are clearly visible through the presence of terminal moraines. Naithani et al., (2001) have observed that recession of snout is very common to most of the glaciers in the Himalayan region and that the recession is irregular in quantity and time of occurrence. Results indicate that all 13 selected glaciers in this study retreated between 1962 to 2001 as indicated in Table 4. Accumulation area for each glacier will vary from year to year depending upon the snow-line altitude at the end of the ablation season. Accumulation area of each glacier is reduced from year 1975 to 2001, whereas ablation area of each glacier is very much increased during 1975 to 2001.Especially in the case of small glaciers including snow/ice which number around 134 in the study area, the accumulation area has also reduced drastically from 1975 to 2001.
Mass balance is one of the important parameter which is influenced by global warming. Mass balance is usually referred to as a total loss or gain in glacier mass at the end of the hydrological year (Heilskanen et al., 2002). Though in the years 1975 and 1992, there is positive specific mass balance but in the year 2001, specific mass balance of all glaciers was negative.

Conclusions
It can be summarized that inventory of the glaciers is of prime interest to evaluate the nature of changes in glacier dimensions and also to establish relationship between climatic change and dynamics of glaciers. As per glacier inventory based on satellite images of September 1975, 1992 and 2001, 13 major glaciers have been chosen for the detailed study in the study area. Total area loss of glaciers from 1962 to 2001 is 18.16%. The glacier G5 and G3 showed 30.48% and 28.91% of the area loss respectively. It is estimated that during last 40 years (1962-2001) majority of glaciers has been retreated. Highest retreat is recorded along G2 (1.3km) and G12 (0.93km) glacier whereas lowest retreat is recorded along G6 (0.24 km), G9 (0.56 km) and G10 glacier (0.55 km). It is to remark that smaller glaciers are retreating at lower pace as compared large glaciers. Most of the glacier snouts are mainly located at more than 4000m. There is general recession of snouts of all the 13 glaciers to various distances. Though in the years 1975 and 1992, there is positive specific mass balance but in the year 2001, specific mass balance of all glaciers was negative above msl.