Surface energy budgets in the Polar Urals of Russia, summer 2015-2017

The Arctic has been warming at an accelerating rate. A significant expansion of larch forests to moss-lichen and heath tundra areas over the past 50-60 years has been documented in western Siberia, with horizontal displacement rates of 32-58 meters per decade and altitudinal rates of 3-4 meters per decade. These vegetation changes may have the potential to impact regional hydrology and climate. Two observation sites (‘tundra’ and ‘trees’) on the eastern slope of the Polar Urals range were selected to represent a natural gradient of land-surface conditions in the tundra-forest transitional zone underlain by continuous permafrost. The ‘tundra’ site is located near the upper east-side corner of a continuous altitudinal transect (Mazepa, 2005) in the vicinity of Tchernaya Mountain near town of Kharp. Moss–lichen tundra with rock outcrops (10-25%) and deciduous shrub communities (up to 0.5 meter high dwarf birch, creeping willow, and northern bilberry) are the dominant land covers. The ‘trees’ site is located in mountain heath tundra encroached by the Siberian larch in the past 30 years, with current surface canopy cover of 20-40%, 3-4 meter average height, and individual trees reaching 8 meters. The sites were instrumented with flux towers and various sensors to continuously record air and surface skin temperature, net radiation, upwelling/downwelling shortwave radiation, relative humidity, and wind speed. In addition, the sap flow signal was measured at the ‘trees’ site.