Spatial variability of glacier elevation changes in the Swiss Alps obtained from two digital elevation models

[1] Massive glacier thinning in the Alps during the past 20 years is documented by direct mass balance measurements on nine regularly observed glaciers. How representative this limited sample of glaciers is for the entire Alps, however, remained uncertain. The near-global digital terrain model from the SRTM enables a closer analysis of this question, which is of fundamental importance to assess overall glacier volume change. Here we present elevation changes from 1985 to 1999 for about 1050 glaciers in the Swiss Alps. The analysis reveals extreme thickness losses (>80 m) for flat/low-lying glacier tongues and a strong overall surface lowering. The mean cumulative mass balance of the nine glaciers with direct measurements (−10.8 m w.e.) agrees well with the mean change of the entire region from DEM differencing (−11 m w.e.) and can thus be considered to be representative. Mean thickness change of individual glaciers is correlated with their size, elevation, and exposure to solar irradiation. This implies that mass losses of large glaciers can be underestimated when they are directly inferred from values measured at much smaller glaciers.