Study of permafrost distribution in Sikkim Himalayas using Sentinel-2 satellite images and logistic regression modelling

Abstract

In this study, Sentinel-2A (S-2A) Multi-Spectral Instrument (MSI) Level 1C (L1C) products are used for identification and mapping of rock glaciers within a transect under observation in Sikkim Himalayas. The mapped rock glaciers were classified on the basis of their activity (intact or relict) and their origin (glacier-derived or talus-derived). Logistic regression models were applied to calculate the probability of permafrost distribution within transect under observation. We observed that freely available high resolution S-2A MSI L1C products are a valuable addition to the already existing freely available high resolution satellite images that can be exploited to study rock glaciers in Himalayan region. The distribution of rock glaciers in Sikkim Himalayas is found to be strongly controlled by elevation and aspect. Topoclimatic conditions above 5000 m a.s.l. are favourable for the presence of permafrost in Sikkim Himalayas. More glacier-derived rock glaciers than talus-derived rock glaciers were observed within transect under observation. Outputs from logistic regression models were capable to reasonably estimate the spatially-distributed probability of permafrost occurrence in the region. However, outputs from these models depended upon the selection of the initiation line location points of rock glaciers and topoclimatic and topographic variables used as predictors for model computation. Based on probability distribution maps, more than 60% (>800 km 2 ) area of transect under observation could contain permafrost. This high areal abundance of permafrost in Sikkim Himalayas suggests increased risks of thawing permafrost under the influence of climate warming in future.