Incorporating moisture content in surface energy balance modeling of a debris-covered glacier

Abstract

Abstract. Few surface energy balance models for debris-covered glaciers account for the presence of moisture in the debris, which invariably affects the debris layer's thermal properties and, in turn, the surface energy balance and sub-debris melt of a debris-covered glacier. We adapted the Interactions between Soil, Biosphere, and Atmosphere (ISBA) land surface model within the SURFace EXternalisée (SURFEX) platform to represent glacier debris rather than soil. The new ISBA-DEBris model includes the varying content, transport, and state of moisture in debris with depth and through time. It robustly simulates not only the thermal evolution of the glacier-debris-snow column but also moisture transport and phase changes within the debris – and how these, in turn, affect conductive and latent heat fluxes. We discuss the key developments in the adapted ISBA-DEB and demonstrate the capabilities of the model, including how the time- and depth-varying thermal conductivity and specific heat capacity depend on evolving temperature and moisture. Sensitivity tests emphasize the importance of accurately constraining the roughness lengths and surface slope. Emissivity, in comparison to other tested parameters, has less of an effect on melt. ISBA-DEB builds on existing work to represent the energy balance of a supraglacial debris layer through time in its novel application of a land surface model to debris covered glaciers. Comparison of measured and simulated debris temperatures suggests that ISBA-DEB includes some – but not all – processes relevant to melt under highly permeable debris. Future work, informed by further observations, should explore the importance of advection and vapor transfer.

The Significance of Convection in Supraglacial Debris Revealed Through Novel Analysis of Thermistor Profiles

“…Thus, accounting for latent heat fluxes, within debris in the context of the Giese et al. (2020) model or a similar moisture content debris model is the next logical step to testing our hypotheses and advancing our understanding of heat flux in supraglacial debris. Such a model could be constrained by the data analysis and nonconductive heat flux constraints that we present in this work.…”

Understanding monsoon controls on the energy and mass balance of Himalayan glaciers

“…However, these thermal properties have been found to be stable during the core monsoon months (Rowan et al, 2020), so we kept k d constant in time at each site in our model. Additional, targeted investigations should examine the possible role of water storage and mobility within debris layers (Giese et al, 2020;Collier et al, 2014).…”

“…Ablation is often expected to be higher on such 'dirty ice glaciers' than at both clean-ice sites and at sites with established debris cover, as shown experimentally (Reznichenko et al, 2010;Östrem, 1959), and by means of modelling (Reid and Brock, 2010), with humidity being a determining factor for this enhancement (Evatt et al, 2015). Moisture in debris is an important factor under monsoonal conditions, controlling the debris' thermal properties and thus ablation (Sakai et al, 2004;Nicholson and Benn, 2006) and has been the focus of devoted modelling studies (Giese et al, 2020;Collier et al, 2014). Moreover, the representation of latent heat due to evaporation (Giese et al, 2020;Steiner et al, 2018) and atmospheric stability correction for turbulent fluxes were shown to be important to improve the simulation of sub-debris melt (Reid and Brock, 2010;Mölg et al, 2012).…”

“…Moisture in debris is an important factor under monsoonal conditions, controlling the debris' thermal properties and thus ablation (Sakai et al, 2004;Nicholson and Benn, 2006) and has been the focus of devoted modelling studies (Giese et al, 2020;Collier et al, 2014). Moreover, the representation of latent heat due to evaporation (Giese et al, 2020;Steiner et al, 2018) and atmospheric stability correction for turbulent fluxes were shown to be important to improve the simulation of sub-debris melt (Reid and Brock, 2010;Mölg et al, 2012). Model implementation, however, remains complex and difficult to validate and transfer.…”

The multi-scale interaction between the atmosphere, cryosphere and extreme topography in High Mountain Asia

“…debris thickness, moisture content, surface roughness; Fyffe et al, 2014) and the contribution of sub-glacial channels to the total melt is not understood (Benn et al, 2017). The limited understanding of basic physical properties, and the high spatial heterogeneity of these glaciers, hinders the development of accurate melt estimates by models (Collier et al, 2014;Giese et al, 2019).…”