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 on
the distribution of palsas and on the area occupied by them is needed to predict changes in landscapes under the influence of
warming and to organize monitoring. However, large-scale maps showing the spread of palsas are very rare. We have
mapped 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 were
noted to warm up to a greater extent in the summer and cool down in the winter. The ground temperature at the depth of zero
annual amplitude is close to 0°C. Landsat satellite images were used as a data source for mapping. Testing of various image
processing methods showed that the highest recognition accuracy was achieved using the Random Forest method (the kappa
coefficient was 0.96). Repeated mapping using an image from another year showed high similarity: the differences in the
selected surface types were less than 2%, which proved the effectiveness of the method. According to the maps, palsas
occupy about a quarter of the research area. This is one of the largest arrays of palsas in the zone of island distribution of
permafrost. Although the site is located in a zone of high-mound peatlands, high-mound palsas are about three times less
common than flat-mound ones, which indirectly indicates their weak stability.