LARGE-SCALE MAPPING OF PALSAS IN THE SOUTH OF THE CRYOLITHOZONE OF WESTERN SIBERIA

Abstract

In the south of the cryolithozone, permafrost, with rare exceptions, is confined to palsas. Accurate data onthe distribution of palsas and on the area occupied by them is needed to predict changes in landscapes under the influence ofwarming and to organize monitoring. However, large-scale maps showing the spread of palsas are very rare. We havemapped palsas in the area of Siberian Ridges in the zone of island distribution of permafrost. In the course of field research,areas with frozen soils were identified, temperature conditions and thawing depth were measured. High-mound palsas werenoted to warm up to a greater extent in the summer and cool down in the winter. The ground temperature at the depth of zeroannual amplitude is close to 0°C. Landsat satellite images were used as a data source for mapping. Testing of various imageprocessing methods showed that the highest recognition accuracy was achieved using the Random Forest method (the kappacoefficient was 0.96). Repeated mapping using an image from another year showed high similarity: the differences in theselected surface types were less than 2%, which proved the effectiveness of the method. According to the maps, palsasoccupy about a quarter of the research area. This is one of the largest arrays of palsas in the zone of island distribution ofpermafrost. Although the site is located in a zone of high-mound peatlands, high-mound palsas are about three times lesscommon than flat-mound ones, which indirectly indicates their weak stability.