Alps-wide high-resolution 3D modelling reconstruction of glacier geometry and climatic conditions for the Little Ice Age

Abstract. Glaciers are crucial indicators of climate change, and reconstructing their past geometries helps to understand past climate fluctuations. Various methods exist for reconstructing past glaciers, including simple power-law scaling and advanced GIS-based techniques that incorporate glacier outlines or surface hypsometry. However, these methods have limitations, such as not explicitly accounting for the physics of ice flow or mass conservation. Numerical glacier models, such as the Instructed Glacier Model (IGM), can overcome these limitations by incorporating ice-flow dynamics and mass conservation. This study presents the first Alps-wide, three-dimensional, model-derived reconstruction of glacier surfaces during the Little Ice Age in the European Alps, a period crucial for understanding pre-industrial natural climate variability. We simulate glaciers to match the empirically mapped Little Ice Age maximum extent at a resolution of 50 m. The simulation of the geometry of all glaciers of the European Alps resulted in a total ice volume of 283±42 km3. The reconstruction reveals regional and local patterns of equilibrium line altitudes derived separately for each glacier. These spatial patterns are influenced by factors such as air temperature, precipitation and shortwave radiation, highlighting the complex interplay of climatic and topographic factors in reconstructing these glaciers and their mass fluxes. A sensitivity analysis indicates an uncertainty of up to 14 % in the total ice volume and minimal sensitivity to parameter modifications for the equilibrium line altitude. Future work could include more sophisticated surface mass balance implementations to better understand the equilibrium line altitude patterns.