Testing the importance of explicit glacier dynamics for mountain glacier change projections

Global glacier models are necessary to project future glacier ice mass loss and the resulting consequences, such as sea level rise. Glacier change is controlled by mass balance, the resulting dynamical geometry adjustments and the interaction between them. The scarcity of ice volume observations makes the calibration, and especially validation, of glacier evolution models difficult. As a consequence, most global models to date used volume/area scaling relations to parameterize dynamical adjustment processes. Over the last years, the increasing accuracy and coverage of global data inventories, in combination with new and automated methods as well as increased computing power allowed for the development of more sophisticated models. This study compares the dynamic response of the global glacier model based on scaling relations by Marzeion et al. (2012) to the globally applicable flowline model based on the Shallow Ice Approximation by Maussion et al. (2019) under controlled boundary conditions. The re-implemented volume/area scaling model is able to correctly simulate glacier changes in response to various climatic forcings. The computed glacier changes are conceptually correct and qualitatively comparable to - but generally smaller than - those of the flowline model. The differences between volume/area scaling model and flowline model are most pronounced for idealized equilibrium experiments and can be attributed to a missing mass-balance-elevation feedback and the overestimation of model-internal time scales. Additionally, these too long time scales result in oscillating adjustments of glacier geometries to step changes in climate. The results of ice volume change projections for Central Europe and High Mountain Asia over the 21st century forced by CMIP6 data are also comparable to the literature, even though on the conservative side. While the values of ice volume change relative to 2020 may differ substantially between the volume/area scaling model and the flowlin
by Moritz Oberrauch
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Masterarbeit University of Innsbruck 2021