Modelling supraglacial debris-cover evolution from the single glacier to the regional scale: an application to High Mountain Asia

Abstract

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.

Controls on the relative melt rates of debris-covered glacier surfaces

“…Radić et al 2014, Huss and Hock 2015, Marzeion et al 2020. New debris thickness datasets offer promise for explicit representation of these areas in glacier models (Kraaijenbrink et al 2017, Compagno et al 2021, Rounce et al 2021, but the spatial variability of supraglacial debris thickness (McCarthy et al 2017, Nicholson et al 2018 and model parametric uncertainty pose considerable obstacles. Furthermore, bare ice exposures (i.e.…”

Projected 21st-Century Glacial Lake Evolution in High Mountain Asia

“…Although the employed parameters are a good compromise for large-scale applications (Maussion et al, 2019), they may lead to overestimated ice volume (Farinotti et al, 2019a). Debris cover on glaciers, which considerably influences glacier mass balance (Rounce et al, 2021), is often investigated at a local scale (Anderson and Anderson, 2018;Rowan et al, 2021) and has only recently been incorporated into a global glacier model (GloGEM, Compagno et al, 2021). Because debris cover can both accelerate and reduce ice loss, we cannot comment at this point on the extent to which debris cover will influence glacial lake formation in HMA in the 21st century.…”

Ice‐Dynamical Glacier Evolution Modeling—A Review

“…By including these physical processes, important feedback mechanisms (e.g., related to the surface elevation and SMB) can be represented. Moreover, an ice-dynamical representation allows for an improved representation of processes such as debris-cover evolution (e.g., Compagno et al, 2022) and mass transfer to glacier tongues of marine-terminating glaciers (e.g., Recinos et al, 2019), which is important for modeling glacier calving realistically.…”