Abstract
Glacier evolution with time provides important information about climate variability. Here we investigate glacier surface velocity in the Himalayas and analyse the patterns of glacier flow. We collect 220 scenes of Landsat-7 panchromatic images between 1999 and 2000, and Sentinel-2 panchromatic images between 2017 and 2018, to calculate surface velocities of 36,722 glaciers during these two periods. We then derive velocity changes between 1999 and 2018, based on which we perform a detailed analysis of motion of each individual glacier, and noted that the changes are spatially heterogeneous. Of all the glaciers, 32 % have speeded up, 24.5 % have slowed down, and the rest 43.5 % remained stable. The amplitude of glacier slowdown, as a result of glacier mass loss, is remarkably larger than that of speedup. At regional scales, we found that glacier surface velocity in winter has uniformly decreased in the western part of the Himalayas between 1999 and 2018, whilst increased in the eastern part; this contrasting difference may be associated with decadal changes in accumulation and/or melting under different climatic regimes. We also found that the overall trend of surface velocity exhibits seasonal variability: summer velocity changes are positively correlated with mass loss, whereas winter velocity changes show a negative correlation. Our study suggests that glacier velocity changes in the Himalayas are more spatially and temporally heterogeneous than previously thought, emphasising complex interactions between glacier dynamics and environmental forcing.
Highlights
15 Glaciers are sensitive to climate variability, and are a major contributor to global sea level rise (Kaser et al, 2010; Kääb et al, 2012; Bolch et al, 2012; Yao et al, 2012; Kraaijenbrink et al, 2017; Ren et al, 2006; Brun et al, 2017)
We found that glacier surface velocity in winter has uniformly decreased in the western part of the Himalayas between 1999 and 2018, whilst increased in the eastern part; this contrasting difference may be associated with decadal changes in accumulation and/or melting 10 under different climatic regimes
We found that the overall trend of surface velocity exhibits seasonal variability: summer velocity changes are positively correlated with mass loss, whereas winter velocity changes show a negative correlation
Summary
15 Glaciers are sensitive to climate variability, and are a major contributor to global sea level rise (Kaser et al, 2010; Kääb et al, 2012; Bolch et al, 2012; Yao et al, 2012; Kraaijenbrink et al, 2017; Ren et al, 2006; Brun et al, 2017). It is of great importance to understand glacier evolution with time since it provides direct evidence for climate change (Kääb et al, 2012; Lutz et al, 2014; Dehecq et al, 2019). Researchers have used satellite altimetry (e.g. Kääb et al 2012; Neckel et al 2014; Kääb et al 2015) and optical satellite stereo imagery (e.g. Brun et al 2017; Maurer et al 2019; Ragettli et al 2016) to quantify glacier mass balance in the Himalayas.
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