The role of supraglacial debris in Himalaya-Karakoram debris-covered glacier systems

Spatiotemporal variability in supraglacial debris properties have the potential to affect estimations of mass balance for debris-covered glaciers. This thesis is concerned with identifying the extent to which debris properties vary in space and time, and the role of these variabilities in estimations of specific mass balance. The research presented uses a combination of methods, including statistical analysis of field data, mapping and classification of thermal and optical remotely sensed data, and numerical modelling. Near-surface debris temperature was measured in the field to investigate short term spatial and temporal variability in debris properties and its influence on debris temperature over a monsoon season. The strongest correlation between timeseries of near-surface debris temperature and meteorological controls was with air temperature, with lesser correlations between rate of change in air temperature and incoming shortwave radiation. Subtle spatial variability was also identified, controlled by site aspect and slope, grain lithology and size, and potentially moisture content and thermal conductance of the bulk debris layer. The occurrence of spatiotemporal variability in supraglacial debris distribution was identified on Baltoro Glacier over a sub-decadal timescale, considered to be primarily due to differences in input of debris to the glacier system through mass movement events. The importance of variability in debris properties was investigated using a surface energy balance and heat transfer model, where the influence of debris thickness, albedo and aerodynamic roughness length was tested. The modelling results, although not directly comparable to mass balance estimates for Khumbu Glacier, showed a 223% increase in total specific mass balance for Khumbu Glacier’s debris-covered area over a monsoon season when a spatially variable debris layer was included. Including spatially variable albedo and aerodynamic roughness length along with debris thickness reduced estimates of specific mass balance, although were still higher than the base line model simulation. Consequently, this thesis confirms the occurrence of spatially and temporally variable supraglacial debris properties, over seasonal and sub-decadal periods, and that such variability is influential for estimates of glacier mass balance.