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Abstract

To compensate for the high computational costs when modelling large-scale mountain glaciers, ice fields or ice sheets over multiple millennia, it is common practice to coarsen the spatial resolution of numerical models to 1 km or more, which is not sufficient to describe complex valley topographies. Here, we examine the influence of spatial resolution by modelling a growing and retreating exemplary ice field in the European Alps at resolutions ranging from 50 m to 2 km using the Instructed Glacier Model (IGM). We find that while ice-covered areas remain similar, ice volume increases substantially with coarser resolution. Compared to the reference run at 50 m spatial resolution, model results at a resolution of 300 m and finer are comparable and sufficiently accurate to simulate topographically constrained ice flow. However, at resolutions coarser than ∼800 m, topographic resampling artificially lowers slope angles and mountain peaks, providing a larger accumulation area at high altitudes, with thicker glaciers that are typically warm-based, while thinner glaciers at fine resolutions remain cold-based. Raised valley floors at coarse resolutions result in slower-flowing ice with increased thickness and glacial response times. The resulting hysteresis between climate forcing and glacial response at coarse resolutions is only partially decreased with slower temperature change. Seemingly stable model results at coarse resolutions may be misleading and accurate glacier geometries might arise from parameter choices that compensate for poorly resolved topography. Similar non-linear and altitudinal-dependent resolution effects are likely in mountain regions worldwide and emphasize the need for model advances to enable simulations at sufficiently high spatial resolutions to accurately resolve glacier dynamics.