Tundra is one of the most sensitive environments of the world in relation to climate changes, since its ecosystems exist close to the limits of plant community tolerance. Besides, tundra vegetation in most of Arctic regions resides on permafrost, which is thermally unstable media. Thus, vegetation and frozen soils are extremely vulnerable to external impacts and are balancing in fragile thermodynamic equilibrium. Thermal and moisture regime shifting lead to changing of thermophysical properties of vegetation cover and thus, the thermal balance of underlying permafrost. In this study we present the results of 2001-2024 in-situ monitoring of vegetation cover and permafrost conditions in remote region of the Chukchi Peninsula, Russian Northeast. The study combines the yearly data on active layer thickness and vegetation cover from two sites of Circumpolar Active Layer Monitoring (CALM) program located within the key site of Eastern Chukotka Coastal Plains (ECCP). The study reveals long-term trajectories of climate, permafrost, and vegetation cover characteristics. Although common biological productivity was growing and active layer was thickening, the particular plant species respond to these changes differently. On sloping plots, the increasing of active layer thickness (ALT) led to correspondent lowering of the permafrost table, drainage of thawing ice and thus, soil drying, which caused the decrease in moss and sedge covers. Meanwhile, within flat poorly-drained surfaces the permafrost thawing contributes to soil moisture with correspondent sedge expansion. Thermokarst-affected terrain triggers the growth of tundra vegetation bioproductivity and serves as a shelter for plants from Arctic winds and facilitates higher snow accumulation.

Permafrost landscapes are particularly susceptible to the observed climate change due to the presence of ice in the ground. This paper presents the results of the mapping and assessment of landscapes and their vulnerability to potential human impact and further climate change in the remote region of Eastern Chukotka. The combination of field studies and remote sensing data analysis allowed us to identify the distribution of landscapes within the study polygon, reveal the factors determining their stability, and classify them by vulnerability to the external impacts using a hazard index, H. In total, 33 landscapes characterized by unique combinations of vegetation cover, soil type, relief, and ground composition were detected within the 172 km(2) study polygon. The most stable landscapes of the study polygon occupy 31.7% of the polygon area; they are the slopes and tops of mountains covered with stony-lichen tundra, alpine meadows, and the leveled summit areas of the fourth glacial-marine terrace. The most unstable areas cover 19.2% of the study area and are represented by depressions, drainage hollows, waterlogged areas, and places of caterpillar vehicle passage within the terraces and water-glacial plain. The methods of assessment and mapping of the landscape vulnerability presented in this study are quite flexible and can be adapted to other permafrost regions.

Permafrost degradation caused by contemporary climate change significantly affects arctic regions. Active layer thickening combined with the thaw subsidence of ice-rich sediments leads to irreversible transformation of permafrost conditions and activation of exogenous processes, such as active layer detachment, thermokarst and thermal erosion. Climatic and permafrost models combined with a field monitoring dataset enable the provision of predicted estimations of the active layer and permafrost characteristics. In this paper, we present the projections of active layer thickness and thaw subsidence values for two Circumpolar Active Layer Monitoring (CALM) sites of Eastern Chukotka coastal plains. The calculated parameters were used for estimation of permafrost degradation rates in this region for the 21st century under various IPCC climate change scenarios. According to the studies, by the end of the century, the active layer will be 6-13% thicker than current values under the RCP (Representative Concentration Pathway) 2.6 climate scenario and 43-87% under RCP 8.5. This process will be accompanied by thaw subsidence with the rates of 0.4-3.7 cm.a(-1). Summarized surface level lowering will have reached up to 5 times more than current active layer thickness. Total permafrost table lowering by the end of the century will be from 150 to 310 cm; however, it will not lead to non-merging permafrost formation.