Abstract ID: 28.7302 | Accepted as Talk | Talk | 2025-02-28 14:45 - 15:00 | Ágnes‐Heller‐Haus/Small Lecture Room

Mountain glaciers are a major contributor to sea-level rise and serve as an important freshwater resource for many mountainous regions. Accurate mass balance estimates are therefore essential for predicting and managing the global and local impacts of climate change. In a warming climate, glaciers will experience increased liquid precipitation and melt, making it crucial to better understand and model the associated surface processes. In this study, we present a modelling approach developed to investigate the dynamic interaction between surface liquid water and glacier mass balance using the SURFEX-ISBA-Crocus model. As Crocus is primarily a snowpack model, some adaptations were necessary for its application to glacier environments. The research focuses on a specific process: the retention of liquid water at the ice surface, which affects both the mass and surface energy budgets. Our implementation temporarily retains liquid water from melt or rain events when glacier ice is exposed at the surface. This water impacts the energy balance and can refreeze over time depending on meteorological conditions. To prevent over-accumulation, excess water is drained according to a predefined coefficient. This process has a significant impact on glacier properties, through the presence of liquid water at the surface and the production of refrozen ice, which directly affects the albedo and mass balance. We applied this new development to Mera Glacier in Nepal to analyse its impact on point mass balance, mass fluxes such as melt and refreezing, and their seasonal variations. The case study highlighted the role of the liquid water reservoir in modulating the effects of melt and rain events. During the pre-monsoon season, the developed model showed greater mass loss due to surface liquid water, which enhanced warming rather than compensating through refreezing. In contrast, during the monsoon and post-monsoon seasons, the behaviour shifted, with the developed version showing less negative mass balance as refreezing increased. The mean annual difference between the two model versions was 0.22m w.e. over the four simulated years, with a larger difference of 0.38 m w.e. observed in 2021-2022. Sensitivity tests on key parameters of the buffer model indicated that the differences are driven not only by the amount of liquid water retained, but also by a positive feedback on albedo, which strongly influences the energy balance. To further validate and refine the method, future work will focus on comparing this modelling approach with observations and measurements.