Spatio-temporal trends in the surface ice velocities of the central Himalayan glaciers, India

The glacier surface ice velocity (SIV) is important in understanding the glacier state. This study presents results on the SIV of the 18 glaciers spread over the Indian central Himalaya (ICH). The SIV was computed by applying Co-registration of Optically Sensed Images and Correlation (COSI-Corr) technique on the Landsat time series data (1993-2017). Results show that the average SIV of all glaciers was 22.63 +/- 5.8 m a(-1) in 1993/94, which decreased (by similar to 23%) to 17.32 +/- 3.1 m a(-1) in 2000/01 and further declined (by similar to 33%) to 11.50 +/- 1.7 m a(-1) in 2015/16. Though a secular decline in average SIV is observed, rates of slowdown are considerably heterogeneous for the studied glaciers being largely determined by glaciers size, orientation, altitude and debris cover. Slope was found to have comparatively low influence on the glacier movement. Inter-regional comparison reveals that average SIVs of the ICH glaciers were slightly but consistently lower than that of the western and eastern Himalayan glaciers. Nonetheless, though moving slowly, ICH glaciers are more active than nearby Everest region glaciers with sufficient proportion of active glaciers (referred as Type-I; 39%). However, the point of concern is that owing to declining health, ICH-glaciers are progressively converting from Type-I to partially active (referred as Type-II), and Type-II to entirely stagnant (referred as Type-III). This observed slowdown coupled with negative mass balance and continuous debris growth (as reported in previous studies) may form favorable conditions for supraglacial lake development. We thereby recommend regular monitoring of glacier dynamics in this region for tenable assessment of climatic change impacts.