Spectral Characteristics of Tundra and Forest Tundra Landscapes during the Years of Summer Temperature Anomalies

The warming at high latitudes that remains in recent years has a direct impact on Arctic and Subarctic landscapes. Possible changes in these landscapes with climate warming are closely related with regulatory mechanisms for the underlying surface temperature. The features of the formation of radiation and evapotranspirational mechanisms of surface temperature regulation in the tundra (from Arctic to southern) and the forest-tundra landscapes of Novaya Zemlya and Western Siberia are studied in this paper. The MODIS data of surface spectral characteristics are used: albedo (Al) and surface temperature (Ts) for July 2000–2019. The radiation mechanism of surface temperature regulation is shown to dominate in glacial and polar desert landscapes of the Arctic and Subarctic with the prevalence of stony and rubble types of surfaces with lichens. At the same time, in the mountainous and Arctic tundra of Novaya Zemlya, the radiative mechanism of surface temperature regulation is practically independent of weather anomalies and currently weakly depends on the surface air temperature trend. In the continental tundra and forest tundra, the evapotranspirational type of surface temperature regulation begins to predominate. This is facilitated by an increase in average monthly air temperatures up to 15–16°C, which favorably affects the diversity of vegetation. In the subzone of the southern tundra and forest tundra, the relation between albedo and surface temperature depends on the height of the terrain, the exposure of slopes, and (especially) on extreme temperature anomalies. In lowlands (hydromorphic complexes), in cold years, against the background of waterlogging, the radiative type of surface temperature regulation prevails, while in warm years, a decrease in humidity leads to the maximal development of vegetation, and the communication mechanism can turn into an evapotranspirational one. At higher elevations, the reverse process, which is also associated with changes in moisture conditions, is observed. In the forest tundra, upon an increase in air temperature and an increase in the height of the vegetation cover, the evapotranspiration mechanism of the relation between the Al–Ts spectral parameters weakens. Thus, in the southern tundra and forest tundra, the existence of two stable positions of equilibrium between the spectral properties of the surface depending on the illumination and temperature anomalies is possible.