Glacier surface velocities in the Jankar Chhu Watershed, western Himalaya, India: Study using Landsat time series data (1992–2020)

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This study presents a spatial and temporal surface velocity analysis of 33 glaciers in the Jankar Chhu Watershed (JCW), western Himalaya. The surface velocity was computed using the Co-registration of Optically Sensed Images and Correlation (COSI-Corr) tool on the Landsat images spanning nearly three decades (1992–2020). Long-term (1948–2018) inter-annual and seasonal climatic trends are also evaluated based on the US NCEP/NCAR reanalyzed gridded data. The role of several topographic and climatic parameters was examined to characterize heterogeneity in velocity.Glaciers in the JCW exhibit three distinct spatial velocity patterns. The type-I glaciers show nearly stagnant (<5 m yrˉ1) debris-covered tongues but a maximum velocity of >60 m yrˉ1 in the debris-free accumulation area. The type-II glaciers exhibit active tongues (>50 m yrˉ1) yet have slow movement in the accumulation zone. The type-III glaciers show prolonged (<10 m yrˉ1) yet consistent movement throughout the flow line. Results show that the average surface velocity of studied glaciers was 11.10 ± 4.1 m yrˉ1 in 1992/93, which increased (by ~43%) to 15.87 ± 2.4 m yrˉ1 in 2000/02 and further increased (by ~59%) to 25.25 ± 1.5 m yrˉ1 in 2017/18. Glaciers show seasonal fluctuations in surface velocities with an apparent “summer speedup” of ~19%–200% compared to the winter velocities. Inter-annual velocities show an increasing trend during the observation periods. Analysis of NCEP/NCAR gridded data also reveals that the temperature increased by 0.55 °C while precipitation decreased by 0.73 mm during 1948–2018.Our results indicate that glaciers remain dynamic throughout their length with systematic spatiotemporal variations in surface velocity that points towards the control of several topographical and morphological factors. The spatially heterogeneous pattern in surface velocity is characterized by zones of high activity crevasses with steep gradients (>30°) showing maximum ice movement at higher elevations, while debris-covered tongues in the low elevations having gentle slopes (<2°) are nearly stagnant. Based on our results and evidences from the literatures, we suggest that seasonal variations (i.e., summer speedup) in surface velocity in the JCW are due to seasonal temperature fluctuations that alter meltwater availability to the subglacial processes akin to the other Himalaya glaciers. An increasing trend in annual velocity manifests the rising trend in temperature in the western Himalaya. Local topographic configuration, combined with regional climatic systems, controls the amount and types of precipitation received in areas like ours to sustain glaciers on a millennial-scale.