Emergence and evolution of a new glacial lake during last climate normal by using remote sensing and GIS in Sikkim, India

Abstract

Glaciers are important indicators of climate change. Melting of glaciers in the Himalayan region has resulted in formation of many glacial lakes. A newly formed lake was observed near the snout of the glacier. This study investigates evolution of this glacial lake using remote sensing satellite data from Landsat mission in last climate normal of around 30 years. Cloud-free data from years 1990, 1996, 2000, 2004, 2010, 2017, and 2021 are used for analysis. Normalized Differential Water Index and Normalized Differential Snow Index thresholding are applied to extract the surface area of the glacial lake and surface glacier cover. It was observed that during beginning of the last climate normal, lake area was 900 m2, and in 2021 it reached 51,300 m2. The clean glacial area decreased from 3,593,700 m2 in 1990 to 3,230,100 m2 in 2021. These changes are indicative of rapid deglaciation and an increase in debris cover as melting ice exposes and deposits debris previously embedded within the glacier. Land Surface Temperature (LST) change was analyzed using empirical equations to understand its relation with observed changes. It was observed that in last climate normal, the average LST was increased by +1.76 °C. The snout regions showed the highest LST change of +3.14 °C. Polynomial, spline and logarithmic regression was applied to access quality of results. A strong correlation between lake area and glacier area was observed with r2 of 0.93. An accuracy of 96.45% was achieved for the estimated changes of the lake with latest field-based result and 96.89% with latest Landsat image. This study successfully generated baseline data for the newly emerged East Rathong Glacial lake during the last climate normal, utilizing normalized differential index time series thresholding of glacier and lake, along with LST change detection.