Modelling supraglacial debris-cover evolution from the single glacier to the regional scale: an application to High Mountain Asia
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2021-08-27
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Abstract
Currently, about 12–13 % of High Mountain Asia's glacier area is debris-covered, altering its surface mass balance. However, in regional-scale modelling approaches, debris-covered glaciers are typically treated as clean-ice glaciers, leading to a potential bias when modelling their future evolution. Here, we present a new approach for modelling debris area and thickness evolution, applicable from single glaciers to the global scale. We implement the module into the Global Glacier Evolution Model (GloGEMflow), a combined mass-balance ice-flow model. The module is initialized with both glacier-specific observations of the debris’ spatial distribution and estimates of debris thickness, accounts for the fact that debris can either enhance or reduce surface melt depending on thickness, and enables representing the spatio-temporal evolution of debris extent and thickness. We calibrate and evaluate the module on a select subset of glaciers, and apply the model using different climate scenarios to project the future evolution of all glaciers in High Mountain Asia until 2100. Compared to 2020, total glacier volume is expected to decrease by between 35 ± 15 % and 80 ±11 %, which is in line with projections in the literature. Depending on the scenario, the mean debris-cover fraction is expected to increase, while mean debris thickness is modelled to show only minor changes, albeit large local thickening is expected. To isolate the influence of explicitly accounting for supraglacial debris-cover, we re-compute glacier evolution without the debris-cover module. We show that glacier geometry, area, volume and flow velocity evolve differently, especially at the level of individual glaciers. This highlights the importance of accounting for debris-cover and its spatio-temporal evolution when projecting future glacier changes.
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Copernicus
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09599 - Farinotti, Daniel / Farinotti, Daniel
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