Slowdown of glacier velocity emerging in the Zanskar Himalayas

Abstract. Trends in glacier surface velocity provide insight into the response of glaciers to climate change as well as local drivers of ice dynamics. The Zanskar Himalayas are heavily glacierised, but retreating glaciers pose a threat to local and regional water security. Remote sensing provides a tool for observing surface velocity over multiple glaciers in a remote and challenging area for field work, providing key observations for tracking changes in this important region. This study provides a comprehensive analysis of long-term (1992–2023) interannual glacier surface velocity and elevation change for 12 selected glaciers in the Zanskar Basin of the Ladakh Himalayas. We show that glaciers have overall experienced deceleration at an average rate of -2.43 m year^-1 decade^-1 in this region. This reduction in ice velocity corresponds with a mean glacier surface elevation decrease of ~ -0.21 m yr^-1 between 2000–2005, increasing to ~ -0.57 m yr^-1 by 2015–2020. While glacier mass loss, particularly through thinning, and associated reduction in driving stress was identified as the primary driver of velocity deceleration, glacier-specific characteristics, such as geometry, topography, debris cover and terminus type, also influenced glacier response. For example, lake-terminating glaciers exhibited local increases in ice velocity near their termini. Overall, our results confirm a reduction in glacier health in this region, as glaciers thin and slow down as a consequence of climate warming.