Explaining recent heterogeneous glacier change in the Annapurna Conservation Area, central Himalayas

Abstract

Since the 1970s, Himalayan glaciers have been shrinking in area, losing mass and decelerating in conjunction with warming air temperatures. This has serious implications for regional water resources. However, recent glacier change has been spatially heterogeneous and significant uncertainty remains about the sources (e.g. supraglacial debris, glacial hypsometry, avalanche-contributing area) of this local variability in the Himalayan glacier response to climate change. This thesis aims to characterise recent glacier changes in the Annapurna Conservation Area (ACA) in central Nepal and identify the extent and sources of local variability in the glacier change signal across a range of spatial (regional-, glacier- and sub-glacier-scale) and temporal (decadal to hourly) scales. Results show widespread glacier area loss (8.5% between 2000 and 2014/15) and mass loss (-0.28 ± 0.24 m w.e. a-1 between 2000 and 2013/16) in the ACA. However, glacier changes were spatially variable, with distinct glacier responses observed between sub-regions in the ACA. Individual glacier change was also modulated by supraglacial debris and glacier hypsometry. However, glacier elevation and avalanche-contributing area only influenced glacier change in the northern part of the study region, indicating that the strength of local controls was not spatially uniform. This thesis also identified another source of glacier response variability in the ACA, of potentially very localised importance, through the documentation of the first surge-type glacier in the central Himalayas. Sabche glacier had a very short surge cycle (~10 years), which is hypothesised to be modulated by subglacial topography, a mechanism that is rarely documented in published literature. Lastly, field data from Annapurna South glacier showed that the temperature and thermal properties of supraglacial debris varied both seasonally and between debris profiles of different thickness, which in turn had an important influence on the timing and magnitude of ablation. Overall, this thesis demonstrates the scale of local glacier change variability in the ACA and shows that the sources of this variability are complex and far from uniform. This work helps to put bounds on the level of noise occurring in the Himalayan glacier change signal and what can be considered a ‘normal’ range of variability. This heterogeneity should be taken into consideration when predicting how Himalayan glaciers will respond to climate change, and the impact of these glacier changes on local communities