Landscape-space analysis of change of thermokarst lakes areas and numbers in the permafrost zone of West Siberia

Methodological questions of thermokarst lakes landscape dynamics in West Siberia permafrost territory based on Landsat space images taken at different time during warm seasons of the period 1973-2008 and GIS-tools were considered. The study used the data on the areas (sizes) of the thermokarst lakes which had developed. This was done by using satellite imagery for 30 test sites, located in different landscape zones and subzones of Western Siberia. Test sites were chosen so as to cover the entire territory of the research more evenly. The research into the multiyear dynamics of thermokarst lakes in West Siberia north was carried out by means of lakes areas measurement using a collection of space images taken at different time in the above 30-year period. Areas of thermokarst lakes on all studied test sites were measured on the basis of satellite images. The total number of lakes was from several hundreds to several thousands. Measurements of lake areas were carried out with the help of geoinformation systems (GIS) ERDAS Imagine 8.3 and ENVI 4.4. The array of measured data was analyzed statistically for thermokarst changes research. Summarized areas of thermokarst lakes were determined on each test site for the observation period for determing relative changes of lakes areas. The dependence of summarized area of thermokarst lakes on each test site at latitudes was determined. The study of multiyear changes of thermokarst lakes showed that in the landscape zones of arctic and typical tundra thermokarst lakes expanded their areas by about 7%. It was shown that in other landscape zones and subzones, lakes areas decreased, on average, by about 10-11%. The data about change of thermokarst lake numbers are given for a 35-year period in different landscape zones and subzones. The total of the disappeared lakes during 1973-2008 made 273. The total area of the drained lakes water surface made 10467.9 hectares in 1973. The area of new lakes changed from 4 to 10 hectares. During the research their quantity made about 8 thousand with the total water surface area 13648.7 hectares. Possible factors of thermokarst lake areas change are discussed. The mechanism of drain water draining from small lakes to large lakes, connected with the acceleration of soil drainage with an increasing temperature is considered, which explains the general shrinking of the lake areas owing to global warming.

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