| Summary: | International audience Thermokarst depressions, called alasses, are an important feature of the periglacial landscape of the Central Siberia. They are considered as a good indicator of cryogenic history of the terrain and of changes in modern hydro-climate conditions. Alasses play a crucial role in the life of the local people providing a habitat for villagers, areas for grazing and for hay-harvest. Alas lake ice is a main source of the potable water during the winter.Our study is based on synergy of different remote sensing techniques, including optical, SAR and altimetric instruments, and in situ observations. We used Landsat imagery, ground trust data and cartographic sources to understand alass lakes and alass grasslands spatial distribution. Then, by retrieving the series of water masks from 30 TarraSAR-X images, we investigated differences in seasonal dynamic of thermokarst lakes in two sub-regions with different rate of permafrost degradation. With help of altimetric radar missions (ENVISAT and Jason-2) provided an information on long-term water level variability in thermokarst lakes and on relative dynamic of their area, the changes of the hydrological conditions during the last 15 years in large 57 000 km2 domain were assessed. Finally, combination of the Landsat derived alass grasland masks with in situ observations on grassland productivity during last 30 years, was used for assessment of the potential ecosystem services provided by the alasses for local agriculture.This work was supported by the CNES TOSCA "Permasensing", SWOT "Wetlands", ERA.NET RUS Plus S&T #226 “ERALECC”, Toulouse Arctic Initiative and University of Toulouse IDEX “InHERA” projects.
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