Permafrost feature and wetness gradient monitoring in Northern Western Siberia

The northern part of Western Siberia has been identified as one of the hotspot areas of climate change across the Arctic. This region is rich in typical permafrost features (thaw lakes, thaw slumps and polygonal features) and stretches across the current transition zone from continuous to discontinuous permafrost for more than 1200 km. These features are characterized by distinct wetness patterns which are expected to alter with permafrost thaw. Remote sensing has been shown of high value for monitoring this region in the past. This included e.g. landcover and ground subsidence analyses. A main constraint for satellite observations is, however, the spatial resolution when working over such large areas. UAV and VHR satellite observations are only available locally but can be used to investigate the impact of the scale mismatch of permafrost features and satellite observations.

A recently developed landcover dataset and subsidence (Sentinel-1) records were investigated for this study. The Circumpolar Landcover Unit (CALU) Database provides highly detailed landcover information with a spatial resolution of 10 meters and consists of 23 thematic units. This level of detail is needed for various applications addressing climate change impacts and ecological research. The used retrieval scheme of landcover units employed provides an unprecedented level of detail. The landcover units have been derived by fusion of satellite data using Sentinel-1 (synthetic aperture radar) and Sentinel-2 (multispectral). These units reflect gradients in moisture and vegetation structure. The available spatial detail of CALU has been already shown to provide the means to assess the complexity of lowland permafrost regions, specifically related to thaw lake variations.

The original CALU database covered the Arctic north of the tree line. The latest version extents towards south, providing additional detail within the tundra-taiga. In addition, about a third of the original extend has been reprocessed (including parts of Western Siberia). Numerous issues of the previous version like data gaps, processing artefacts and minor misclassification cases were addressed.

Eventually, the satellite derived information has been compared to VHR data, specifically for polygonal tundra. A database including a range of relevant properties (e.g. low centered versus high centered polygons) has been created for this purpose, covering 25 sites sized 1x1 km with polygonal peatlands spread for 30 kilometers from north to south in the northern part of the Pur-Taz interfluve. Permafrost properties of this area are rapidly changing: while it was considered to be continuous in 1991, it is now discontinuous according to CCI Permafrost data. Statistics based on wetness gradients and landcover for polygonal and non-polygonal features were analyzed. Differences in typical wetness gradients between these features were found to be more pronounced in subsidence retrievals than in landcover.

CALU: Bartsch, A., Khairullin, R., Efimova, A., Widhalm, B., Muri, X., von Baeckmann, C., Bergstedt, H., Ermokhina, K., Hugelius, G., Heim, B., Leibman, M., & Gruber, C. (2024). Circumarctic Landcover Units (2.0) [Data set]. Zenodo. https://doi.org/10.5281/zenodo.14235736