GPR-derived ice thickness of the temperate Hintereisferner glacier (Austrian Alps): evaluation of thickness models

Abstract. Alpine glaciers are retreating rapidly and have a potential for near complete ice loss at the end of the 21st century thus accurate glacier evolution models are crucial for predicting the magnitude and rate of future glacier changes. Without reliable ice thickness assessments, such models lack credibility and cannot be validated, thus here we evaluate several ice thickness models and present new ground-penetrating radar (GPR) ice-thickness measurements of the Hintereisferner – a temperate glacier located in the Ötztal Alps, Austria, which despite of being one of the WGMS reference glaciers lacks up-to date measured ice thickness data. The GPR data is characterized by strong signal scattering, typical for temperate ice with high water content, however the glacier bed is detectable in most profiles. GPR measurements reveal a maximum ice thickness of ~160 m along the central flowline and a mean thickness of ~81 m across the surveyed area. We further select three widely used, open-source ice-thickness models, GlabTop2, OGGM, and Millan et al. (2022), and compare their output to the GPR-derived ice thickness. All models systematically overestimate ice thickness across the surveyed area, with mean positive biases of ~37–40 m for GlabTop2 and OGGM and ~59 m for the Millan model, while only minor and localized underestimation occurs along the central flowline. These results highlight the limitations of predominantly geometry-based and velocity-informed modelling approaches when applied to small, temperate valley glaciers, where ice rheology and basal conditions may have greater influence on the resulting thickness than these algorithms allow. The GPR data presented here is made freely available in the section “Code and data availability” and provides an updated ice thickness benchmark for the Hintereisferner, to be used for future model calibration and improvement for Alpine glacier evolution projections.