Exploring the causes of glacier velocity anomalies in High Mountain Asia: Analysis from the Karakoram, Spiti Lahaul and Eastern Himalaya

Glaciers in High Mountain Asia (HMA) have been experiencing enhanced mass loss and velocity slowdown since the late 1990s, coincident with rising global and regional temperatures. In each HMA region with distinct climatic characteristics, the dynamical responses of glaciers vary substantially; yet these intra-regional variations are overlooked in regional assessments due to large-scale oversampling. In particular, the role of glacier morphological factors (e.g. size, elevation, hypsometry) in causing the different responses is poorly understood.

We investigated the velocity changes of the glaciers in three regions — the Eastern Himalaya, Spiti Lahaul, and Karakoram — between 2000 and 2016 in order to understand the key components of glacier sensitivity and their relationship with glacier morphology. Using the NASA Inter-Mission Time Series of Land Ice Velocity and Elevation dataset as input, we extracted glacier-specific velocities (and associated errors) using a bespoke MATLAB script, and compiled these into “mean annual velocity anomaly” series following established methods. Anomalies were analysed with glacier morphometric parameters using a linear regression approach, with statistically significant relationships identified.

Our results show that mean velocity anomaly within the Eastern Himalaya varies with glacier aspect, with mean annual anomalies of 0.09 ± 2.32 m yr^-1 per year for north-flowing glaciers and –0.1 ± 1.59 m yr^-1 per year for south-flowing glaciers. Glaciers in the Karakoram also show opposing trends, with anomalies of –0.86 ± 5.69 m yr^-1 per year and –3.23 ± 2.53 m yr^-1 per year in the north west, and 1.00 ± 3.80 m yr^-1 per year in the south east. Glacier slowdown in Spiti Lahaul is –0.37 ± 4.50 m yr^-1 per year, and we do not document contrasts in intra-regional glacier response. Overall, glacier size, minimum elevation and hypsometric integral are the most significantly correlated parameters to mean velocity anomaly. Percentage and area of debris, flow line length, slope and termination environment were also found to be important autocorrelations. Importantly, we find no consistent morphometric interactions contributing to glacier anomaly between all three regions, implying that glacier responses are unique and a cumulative product of their morphometric variability.