Glacier fraction map

The glacier fraction map can be calculated from a vector file with glacier outlines. In QGIS from the Processing toolbox, select the “v.to.rast.value” tool like in the previous section.

Select your glacier outlines as vector input layer and convert it to raster at the same extent of the clone map. Set the cellsize at a lower value than your model resolution. For example, if your model cell size is 200 m, select 20 m for the converted raster.

The “nodata” values need to be reclassified to zeros. To do this use SAGA’s Reclassify tool from the Processing toolbox. You can easily find it by typing Reclassify in the search field.

Figure 39: Reclassify tool

In the dialog box set all values to 0.0, and set “replace no data values” to “Yes”, set “new value for no data values” to 0.0 and set “replace other values” to “No”. Select an output filename and click “Run”.

Figure 40: Reclassify tool dialog box

Now we aggregate the fine resolution grid with glaciers to the model resolution. This can be done using the “r.resamp.stats” tool selected under Processing Toolbox 🡪 GRASS commands 🡪 Raster 🡪 r.resamp.stats.

Figure 41: GRASS aggregation tool

In the dialog box, set the fine resolution glacier grid as input raster layer and choose aggregation method “average”. Import the processing extent from the clone map and set the cell size to the model resolution (in the screenshot below it is 200m as in the example of the Trisuli case study).

Figure 42: GRASS aggregation tool dialog box

The resulting grid can be converted to a PCRaster map using step 8 from Section 5.3.