Review of glacial lake inventories in the Sikkim Himalaya

This article aims to review the existing research associated with the preparation of glacial lake inventories in the Sikkim Himalaya, to understand their evolution over the past two decades and analyse them. The number and areal extent of glacial lakes has been increasing in the Sikkim region due to climate change and global warming in the Himalayas. This makes glacial lakes vulnerable to the occurrence of Glacial Lake Outburst Floods (GLOF). This review analyses the findings from 30 research studies of glacial lakes, including key parameters, such as temporal coverage, criteria for lake delineation (including minimum size thresholds), lake typology criteria, remote sensing data sources, and methodologies employed for glacial lake identification and also the GLOF analysis. The review highlights inconsistencies such as variations in data sources, automatic or semi-automatic mapping technique, minimum size criteria and need for expert interpretations. The study finds that Normalised Difference Water Index (NDWI) based identification of glacial lake is the most preferred technique with visual interpretation. It is also observed that the source of water for a glacial lake is the prominent typological criterion for both glacial lake mapping and GLOF analysis. This study highlights the possibility of preparing a comprehensive inventory of glacial lakes having at least 0.0036 km2 area from 1962. Such inventory may further improve our understanding of glacial lake dynamics and facilitate an effective GLOF risk analysis in the Sikkim region.