REGIONAL UNEVENNESS OF THE SUMMER WARMING IN THE CONTINENTAL ARCTIC AS AN INDICATOR OF NATURAL BOUNDARIES OF NORTHERN LANDSCAPES

The authors have revealed the features of summer warming in different sectors of the Russian Arctic zone in the modern period and the near future. In connection with the considered features of the summer warming within 1991—2018, the researchers present a unique analysis of the inter-decade distribution of trends in the characteristics of the natural zones surface (vegetation index, total evapotranspiration, surface temperature, albedo). Changes in climatic conditions provide prerequisites for a change in the spectral characteristics of landscape zones, especially in the central sector of the Russian Arctic zone. The warming analysis is based on an assessment of temperature trends and the evection in latitude of the isotherm +10°С in the summer months. According to the physiographic approach, the southern border of the tundra runs approximately along the July isotherm +10°. Under warming conditions, such an indicator is the key one for determining changes in heat supply and vegetation growth in northern landscape zones. During 1991—2018 in the Russian Arctic zone, the isotherm +10°С was moving northwards, increasing from decade to decade. The maximal shift of the isotherm +10°С is noticeable in June in the western and central sectors of the Russian Arctic, resulting in the surface temperature growth and the increase of a zone with active plant vegetation. As a result, positive trends of NDVI and evapotranspiration, as well as negative trends of albedo, reach their maximum values in the forest- tundra of Western Siberia and the tundra of Taimyr. At the same time, in July the shift of the isotherm +10°С is minimal over most of the territory, which is reflected in the minimum changes in the surface spectral characteristics. In August, the isotherm position significantly fluctuates between the decades. Model forecasts assume that in the next decade of 2031—2040 against the background of ongoing warming, fluctuations in the isotherm position in July are expected to be within the standard deviation of the end of the 20th century (1991—2000). In June and August, a more noticeable shift to the north of the isotherm in the western sector of the Arctic zone is possible, which implies a further increase of the active vegetation zone here and a change in the surface spectral characteristics.

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