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In the following, we provide the list of technical requirements for the glacier area product according to the Global Climate Observing System (GCOS) requirements for the Essential Climate Variable (ECV) ‘Glaciers’ (Table 1) that is taken from GCOS (2022). Most important here is the required uncertainty of the glacier outlines (better than 5%) which can only be reached by manual editing as e.g. debris-covered glacier parts are not included by the automated mapping and can easily cover 50% or more of the glacier area.
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Figure 1: Glacier coverage and the 19 first-order regions in RGI v7.0 showing regions of improvement in red and unchanged regions in blue The image is taken from [RD1].
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Figure 2: Size-class distribution in RGI 6.0 (blue line) and 7.0 (red line). The image is taken from [RD1].
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Table 1: GCOS requirements for the ECV Glaciers.
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Methods to obtain the uncertainty of the digitized glacier outlines are described by Paul et al. (2013 and 2017).
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Below, we illustrate with selected examples how the vector datasets look like and how they can be displayed. Table 3 illustrates a subset of the information stored for each glacier in the attribute table of the shape file. Apart from just overlaying glacier outlines on a satellite image, one can also colour-code the range of values for a specific attribute within the glacier outlines (Figure 3a) or as filled circles (Figure 3b). The values can also be arranged in histograms, for example to reveal the size-class distribution of glaciers in a region (Figure 4a) or in scatterplots (Figure 4b), revealing possible dependencies among selected attributes. The topographic information can be used to derive several further glacier characteristics (e.g. Haeberli and Hoelzle 1995) or climatic information (Sakai et al. 2015).
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Table 3: Screenshot of the information provided in the attribute table for each glacier. The lower panel is the right continuation of the upper panel. Click on the table for full size image.
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Figure 3: a) Colour-coded mean glacier aspect for glaciers of the Jostedalsbreen Ice Cap in southern Norway. The abbreviations in the legend stand for the terrain aspect orientation: N for North, NE for North-East, E for East, SE for Sout-East, S for South, SW for South-West, W for West and NW for Noth-West. b) Median elevation of glaciers in the Alps represented as colour-coded circles (from Paul et al. 2020). Click on the figure for full size image.
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