Glacier Extent and Volume of Glacier-Stored Water in the Indian Himalaya
In the Himalaya, glacier inventory has been published by numerous research workers (Kulkarni and Buch 1991; Sangewar and Shukla 2009; Bajracharya and Shrestha 2011; Arendt et al. 2012). These studies suggest that the glacial extent in the Indian Himalaya is between 20,785 and 27,915 km2, indicating large discrepancies in the estimates (Fig. 1). These discrepancies are possibly due to the difference in the time period, scale and methodology of mapping. One of the earliest inventories was carried out in the year 1991 by the Space Application Centre (SAC-ISRO) (Kulkarni and Buch 1991) using satellite data of year 1987, estimating an areal extent of the glaciers in the Indian Himalaya as 23,314 km2. Subsequently, the Geological Survey of India (GSI) also published an inventory using topographic maps and aerial photographs taken in the year 1962-1963 (Sangewar and Shukla
2009). It estimates an areal extent of the Indian Himalaya as 26,775 km2. The difference in SAC and GSI estimates could be because the glacierets were not mapped in the SAC inventory and also, possibly due to the difference in methodology. In the due course, the inventories by the International Centre for Integrated Mountain Development (ICIMOD) and Randolph Glacier Inventory (RGI) were also published, suggesting an areal extent of glaciers in Indian Himalaya as 20,785 and 27,915 km2 respectively, (Bajracharya and Shrestha 2011; Arendt et al. 2012).
Fig. 1 Comparison of areal extent of glaciers in the Indian Himalaya mapped by the International Centre for Integrated Mountain Development (ICIMOD), Space Application Centre (SAC), Geological Survey of India (GSI) and Randolph Glacier Inventory (RGI) (Bajracharya and Shrestha 2011; Kulkarni and Buch 1991; Sangewar and Shukla 2009; Arendt et al. 2012)
However, as the ICIMOD and RGI inventories are available in digital form, they were further analysed to assess their accuracies in the Baspa basin, Himachal Pradesh. The glacier outlines were manually interpreted using Landsat imagery of 2013 and 2014. The glacierised area was estimated at 194 ± 14 km2. The gla- cierised extent of Baspa basin recorded by the inventory of ICIMOD and RGI 4.0 suggests an area of 163 ± 12 and 193 ± 16 km2, respectively. As RGI glacier outlines are closer to our interpretation, RGI outlines were further used to assess glacier volume in Indian Himalaya (Fig. 2). RGI is a compilation of glacier boundaries from different agencies and covers almost all glaciers around the globe.