Glacier and Snow Studies in Sikkim Himalaya Using Remote Sensing Techniques

Abstract

With limited knowledge on snow and glacier studies in Eastern Himalaya, this study brings out a comprehensive and systematic understanding of the role of cryosphere in the Himalayan state of Sikkim. This study focuses on the long-term monitoring of (i). snow cover distribution, and (ii). glacier area change assessment, presented for the first time. Initially, to understand the distribution of snow and glaciers in the Tista basin of Sikkim, a glacier inventory was prepared, which is discussed in the first part of the thesis, using topographical maps of 1962-66. Hand tracing and cartographic techniques were used for mapping the glacial features. This provided a baseline historical information on the distribution of glaciers, snowfields and lakes in the basin, which yielded 91 glaciers, 215 snowfield and 259 glacial, non-glacial and supraglacial lakes, covering 501.51 km2, 160.51 km2, and 12.39 km2, respectively. The second part of the thesis deals with a long term snow cover monitoring, between 2002 and 2010. The snow cover was monitored (i). monthly, (ii). seasonally, and (iii). annually, for a ten year period. This makes it possible to understand the decadal changes in the seasonal snow cover in the Sikkim Himalaya, which was estimated using 429 enhanced MODIS snow product. The major findings showed (i). 33 % of Sikkim under snow cover area, with (ii). maximum snow cover of 50 % in February, (iii). substantially high snow cover area in November ( 40 %). The third part of the thesis focuses on the long term glacier monitoring, for a 20 year period, between 1990 and 2010. The glacier area assessment and change detection was carried out using multi-temporal satellite images of Landsat and LISS III. A combination of visible, near infrared and short wave infrared multispectral data, combined with image enhancement technique was used for glacier mapping. In addition, the effect of various parameters such as debris cover, moraine dammed lakes, and area altitude of glaciers was studied to understand their role on glacial retreat. The analysis showed that debris covered glaciers retreat less, but the influence of lakes on debris covered lakes accelerates retreat. ix The overall study showed: (i). a decadal decrease of 2.98 1.83 % in the snow cover area, (ii). a decadal decline of 8.30 5.19 % in wintertime snow cover area in December, between 2002 and 2011, (iii). a loss of 6.6 0.38 km2 ( 0.16 % per annum) in glacier area, and (iv). an increase of 2.98 0.27 km2 in the lake area, between 1990 and 2010. These phenomena could be related to a 1.0 C rise in the summer minimum temperature, a 2.0 C rise in the winter minimum temperature, and a decline in the winter precipitation, observed in the region. The hotter summers and warmer winters, accompanied by a slight decrease in the winter precipitation, could enhance a prolonged melting season. The results of this research help in an understanding of the snow cover pattern and glacier area changes in Sikkim Himalaya, a region less studied. The results of this research are further useful for assessing the sensitivity of climate and local environment to the snow pack ablation, snowmelt, glacier retreat, increase in debris cover and glacial lake expansion, which influences stream runoff patterns, important for optimal management of water resources.