Lilian Schuster , David Robert Rounce, Fabien Maussion

Glacier models contribute significantly to the uncertainty of glacier change projections. In this study, we focus on temperature-index mass-balance (MB) models and their calibration, exploring the impact of various design choices on projections. Using the Open Global Glacier Model (OGGM), we compare the effects of different surface-type dependent degree-day factors, temporal climate resolutions (daily, monthly) and downscaling strategies (temperature lapse rates, temperature and precipitation correction) on projections for 88 glaciers with in-situ observations. Our analysis shows that higher spatial and temporal resolution MB observations lead to more accurate MB gradient representations thanks to an improved calibration. Some choices have systematic effects. For example, weaker temperature lapse rates result in smaller glaciers in a warmer climate. However, we often find nonlinear effects, such as with the sensitivity to different degree-day factors for snow, firn, and ice, which depends on how the glacier accumulation area ratio changes in the future. Similarly, using daily versus monthly climate data can have opposite effects on different glaciers. Our study highlights the importance of considering minor model design differences to predict future glacier volumes and runoff accurately. However, the lack of independent observations limits our ability to evaluate the added value of additional model complexity.