Heterogeneity in topographic control on velocities of Western Himalayan glaciers

Anshuman Bhardwaj,Manfred F Buchroithner,Lydia Sam,F Javier Martín-Torres,Rajesh Kumar

doi:10.1038/s41598-018-31310-y

Anshuman Bhardwaj, Manfred F Buchroithner + Show 3 more

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https://doi.org/10.1038/s41598-018-31310-y

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Abstract

Studies of the seasonal and annual patterns of glacier velocities improve our understanding of the ice volume, topography, responses to climate change, and surge events of glaciers. Such studies are especially relevant and equally rare for the Himalayan glaciers, which supply many rivers that sustain some of the most heavily populated mountainous regions in the world. In particular, the control of the hypsometric distribution of geomorphometric parameters, such as slope, aspect, and curvature, on the dynamics of Himalayan glaciers have never been studied so far, at the river basin scale. Here, we present the degree to which topographic and hypsometric parameters affect the seasonal and annual average flow velocities of 112 glaciers in the Baspa River basin in the Western Indian Himalaya by analysing Global Land Ice Velocity Extraction from Landsat 8 (GoLIVE) datasets for the years 2013–2017. We observe, (i) significant heterogeneity in topographic controls on the velocities of these glaciers, (ii) elevation and the seasons play important roles in regulating the degree to which morphometric parameters (slope, aspect, and curvature) affect these velocities, (iii) a possible polythermal regime promoting both sliding and deformational forms of motion in a majority of these glaciers, and (iv) a detailed analysis of complex topographic controls within various elevation zones using a novel hypso-morphometric approach. These findings can help us to better model the dynamics of Himalayan glaciers and their responses to the future climatic scenarios. The inferences also suggest the need to incorporate dynamic topography in glacio-hydrological models in the wake of constant glacial evolutions.

Highlights

Global glacier monitoring is pertinent for observing the direct impacts of changes in climate on water security and future sea levels[1]
(i) we segregated the available GoLIVE data (Fig. 2a) according to the hydrological seasons in the study area determined from published field runoff measurements[40] and long-term temperature records (1985–2007) from the Rakchham (3045 m asl) observatory (Fig. 2b) marked in Fig. 1a40. (ii) We established optimal thresholds for the corr (>0.4) and del_corr (>0.3) rasters, based on the available field velocity measurements[33,38] for various seasons. (iii) Further, we discarded any seasonal or annual average velocity pixels that are over 2 standard deviations (2 SDs) of the velocity values, in order to use only the most reliable velocity values in our analyses
(iv) we performed Ordinary Least Squares (OLS) linear regression analyses (Supplementary Fig. 1) before and after the 2 SD thresholding to observe improvements and the degree of topographical controls as explanatory variables for velocities, and to perform additional thresholding of the pixels that show the smallest degree of topographic control by excluding ±1 SD of the standardised residuals for the OLS-modelled velocities compared to the GoLIVE velocities

Summary

Introduction

Global glacier monitoring is pertinent for observing the direct impacts of changes in climate on water security and future sea levels[1]. Our study aims at determining the extent of topographic and hypsometric controls on the seasonal and annual average flow velocities of 112 glaciers of Baspa River basin in the Western Indian Himalaya (Fig. 1) that were sufficiently large to encompass at least one representative velocity pixel from the GoLIVE products and to permit the reliable extraction of second-order geomorphometric derivatives[36] (see Methods) The glaciers in this river basin have been extensively studied for remote sensing-based mapping[37,38], glacier dynamics[33], glacial lakes[39], and runoff estimations[40]. The highest glacier velocities were observed during the melting and pre-melt seasons, followed by the post-melt season, which highlights the influence of westerly-derived winter accumulation on the cumulative dynamics of the glaciers in this part of the Himalaya

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