Abstract
Knowledge on ice thickness distribution and total ice volume is a prerequisite for computing future glacier change for both glaciological and hydrological applications. Various ice thickness estimation methods have been developed but regional differences in fundamental model parameters are substantial. Parameters calibrated with measured data at specific points in time and space can vary when glacier geometry and dynamics change. This study contributes to a better understanding of accuracies and limitations of modelled ice thicknesses by taking advantage of a comprehensive data set of in-situ ice thickness measurements from 58 glaciers in the Austrian Alps and observed glacier geometries of three Austrian glacier inventories between 1969 and 2006. The field data are used to calibrate an established ice thickness model to calculate an improved ice thickness data set for the Austrian Alps. A cross-validation between modelled and measured point ice thickness indicates a model uncertainty of 25-31% of the measured point ice thickness. The comparison of the modelled and measured average glacier ice thickness revealed an underestimation of 5% with a mean standard deviation of 15% for the glaciers with calibration data. The apparent mass balance gradient, the primary model parameter accounting for the effects of surface mass balance distribution as well as ice flux, substantially decreases over time and has to be adjusted for each temporal increment to correctly reproduce observed ice thickness. This reflects the general stagnation of glaciers in Austria. We applied optimized apparent mass balance gradients to all glaciers of the latest Austrian glacier inventory and found a volume of 15.9 km³ for the year 2006. The ten largest glaciers account for 25% of area and 35% of total ice volume. An estimate based on mass balance measurements from nine glaciers indicates an additional volume loss of 3.5 ± 0.4 km³ (i.e. 22 ± 2.5%) until 2016. Relative changes in area and volume were largest at glaciers smaller than 1 km², and relative volume changes appear to be higher than relative area changes for all considered time periods.
Highlights
Climate observations as well as climate scenarios reveal a rise of temperatures around the globe (IPCC, 2014), with almost twice the global rate in the Alps, and, for example, in Austria (Auer et al, 2007; APCC, 2014)
This study provides a state-or-the-art estimate of ice volume for all Austrian glaciers based on ice thickness modeling calibrated with all existing ice thickness measurements
A comprehensive data set of in-situ ice thickness measurements at 58 glaciers and data on glacier surface elevation and extent from three glacier inventories (GI) between 1969 and 2006 was used
Summary
Climate observations as well as climate scenarios reveal a rise of temperatures around the globe (IPCC, 2014), with almost twice the global rate in the Alps, and, for example, in Austria (Auer et al, 2007; APCC, 2014). Assessments of anticipated sea-level rise caused by glacier mass loss importantly depend on initial ice volume estimates (e.g., Marzeion et al, 2012; Radicet al., 2014; Huss and Hock, 2015). Most regional and global glacier models estimate initial ice volume applying simple volume-area scaling relations (e.g., Bahr et al, 1997; Radicand Hock, 2010; Bahr et al, 2015) on the basis of global glacier inventories (GI) (e.g., Pfeffer et al, 2014). Huss and Farinotti (2012) presented the first estimate of ice thickness distribution for all roughly 200’000 individual glaciers on Earth allowing the application of a global glacier-specific model for future sea-level rise and the response of glacier runoff (Huss and Hock, 2015, 2018) A considerable variability among the individual approaches has been found when not calibrating against withheld ice thickness measurements. Huss and Farinotti (2012) presented the first estimate of ice thickness distribution for all roughly 200’000 individual glaciers on Earth allowing the application of a global glacier-specific model for future sea-level rise and the response of glacier runoff (Huss and Hock, 2015, 2018)
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