Influence of topography on glacier changes in the central Himalaya, India

Assessing the impact of topography on glacier changes is vital because, while climate is the driving force behind these changes, the topography may control their heterogeneity. Present study provides a detailed insight into varied responses of 18 glaciers (1994-2015), spread over the central Himalaya (CH), and systematically explores the influence of topographic factors on changing glacier parameters using satellite remote sensing data (Landsat TM/ETM + /OLI, Cartosat-1 PAN, Resoursesat-2 LISS-4, SRTM digital elevation model) and limited field observations. Results show that the total glaciated area decreased from 313.34 +/- 7.95 km(2) in 1994 to 306.36 +/- 8.04 km(2) in 2015 whereas retreat rates varied from 4.75 +/- 2.25 to 28.25 +/- 2.25 m a(-1) during this period. The total debris-covered area also increased from 86.56 +/- 1.29 to 97.99 +/- 1.75 km(2) and the average snowline altitude upshifted by 67 m during 1994-2015. Various topographic factors analyzed here include: glacier area, length, compactness ratio, altitude, slope, aspect, hypsometry, area accumulation ratio and snout characteristics. Multivariate statistical analysis demonstrates that compactness ratio, glacier size, altitude range and mean slope strongly influence the area loss. Whereas glacier length, mean slope, compactness and altitude range influence the retreat rates. Cumulative influence of these factors was assessed using a novel approach which uses ordinal scale relative weighting-rating technique to compute a Topographic Influence Index (no. Breaks in the frequency of TII values were used for categorizing the glaciers into three groups that experienced different degrees of topographic influence on area loss and retreat namely, modest, moderate and strong. It is observed that, out of 18 glaciers, 5 had modest, 8 had moderate and 5 glaciers had strong influence of topography on area loss. Whereas, 6, 8 and 4 glaciers experienced modest, moderate and strong influence of topography on retreat, respectively. Further, we found that similar to 78% and similar to 61% glaciers in case of area loss and retreat, respectively, are also the ones which exhibit higher glacier wastage. This indicates that the observed heterogeneity in the response of studied glaciers is probably topographically induced.