ИСТИНА

Thermokarst lakes dynamics is arguably an indicator of cryolitozone reaction to climate warming. Recent studies show various results, which are interpreted as thermokarst activization but it could be also due to errors. We have developed a method for reliable measurements of thermokarst lake area changes and applied it for various regions, taking in account regional factors. The method compares multitemporal Landsat images, taken throughout the warming period from the 1970s. Different resolution of images forced us to exclude small lakes from analysis, and to use maps (rather than total area statistics) to analyse geographic distribution of emerging and disappearing areas of water. We investigated nearly 40 test sites in all 6 regions of Russian cryolithozone and compiled 40 maps of thermokarst lakes dynamics with over 300 000 lakes. In total we observe small and variable dynamics for 1970-2000 – some lakes decreased (by 2.9%) and some increased (by 1.2%). Mass area decreases were due to drainage of lakes by rivers. Lakes increases were due to activisation of thermokarst in regions with highly icy permafrost (Yamal, Yana-Indigirka lowland). Filling up by rivers acts everywhere, especially at Kolyma lowland, Yana and Indigirka deltas, Transbaikal hollows. Cyclic changes of precipitation control lakes dynamics in CentralYakutia. Anthropogenic impact caused lakes changes in regions of oil and gas extraction in Western Siberia. We conclude that thermokarst lakes dynamics is controlled by multiple factors and so cannot be used as an indicator of climate warming impact at cryolitozone.