Investigations on physical properties and ablation processes of snow cover during the spring snowmelt period in the headwater region of the Irtysh River, Chinese Altai Mountains

摘要

To explore the effects of the underlying surface on snow properties and the "forest effects'' on snow accumulation and ablation processes in the headwater area of the Irtysh River in the Chinese Altai Mountains, the physical properties of snow and certain snowmelt processes were investigated during the snowmelt period in 2014. Our observations showed that the diurnal and daily variations of air and snow temperatures, the liquid water contents (LWCs), and the densities of surface snow layers at 0-5 cm depths were in agreement, but differences in snow properties were obvious at the bottom snow layers. The LWCs were divided into three categories according to snow temperature (T-s): LWC = 0, T-s <-3 degrees C; LWC <1 %, -3 <= T-s <-1 degrees C; LWC <7 %, T-s -1 degrees C. The snow densities were greatest in the top layers above all underlying surfaces (grassland, concrete, and river ice) during the snowmelt period. The snowmelt experiment indicated that the mean air temperature was the highest on the grassland and lowest in the glade, but the diurnal temperature range was the lowest in the continuous forest and highest on the grassland. The canopy snow interception rate of Abies sibirica reached up to 70 % and the mean value of the continuous forest cover was about 30 %. The snowmelt duration periods were 20 days on the grassland, 35 days in the continuous forest, and 43 days in the forest glade, and the corresponding average snow melt rates (SMRs) were 2.1, 1.2, and 1.4 mm d(-1). For one single A. sibirica tree, the SMR in the sub-canopy was only half that on the edge and outside of the forest canopy.