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Predicting the fate of mountain glaciers requires reliable observational data to test models of glacier mass balance. Using glacier extents and digital elevation models (DEMs) derived from aerial photographs and ASTER satellite imagery, we calculate changes in area, elevation, and volume of Tiedemann and Klinaklini glaciers. Between 1949 and 2009, Tiedemann and Klinaklini glaciers lost approximately 10% of their area. The total area-averaged thinning of Klinaklini was 40.1 ± 1.5 m water equivalent (w.e.) and total mass loss equaled 20.24 ± 1.36 km 3 w.e., whereas Tiedemann Glacier thinned by 25.7 ± 1.9 m w.e. and lost 1.69 ± 0.17 km 3 w.e. of ice. We attribute lower observed rates of thinning at Tiedemann Glacier to thick debris cover in the ablation area. Both glaciers thickened at mid-elevations after the year 2000. Glacier mass balance and volume change were modeled using temperature, precipitation and evapotranspiration fields dynamically downscaled to the mesoscale (8 km resolution) using the Regional Atmospheric Modeling System (RAMS) model and further statistically downscaled to the glacier scale (100 m elevation bands) using modeled surface lapse rates. The mass balance model over-predicts total volume loss by 1.1 and 6.3 times the geodetic loss for Klinaklini and Tiedemann glaciers respectively. Differences in modeled and observed total ice loss are due to (1) the coarse resolution of the downscaled climate fields, and (2) extensive debris cover in the ablation area of Tiedemann Glacier. Future modeling efforts should dynamically downscale at resolutions that capture the topographic complexity of a region and employ strategies to account for time-evolving debris cover. |
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