The effects of forest litter on snow energy budget in the Tianshan Mountains, China

摘要

Forest litter exerts an impact on the energy budget of snow surfaces, which lie beneath forest canopies. In this study, we measured shortwave and longwave radiation levels, as well as quantities of Asian spruce (Picea schrenkinan) forest litter, over 3 snow study plots that representing an open environment, 20% forest canopy openness (20% FCO), and 80% forest canopy openness (80% FCO). The fractional litter coverage (lc) was obtained through the binarization of digital photographs of forest litter. The effects of forest litter on snow surface albedo (alpha), snow surface temperature (T-s), upward shortwave and longwave radiation (K-up arrow and L-up arrow), and sensible heat flux (H) were then analyzed. According to our results, the energy budget over snow surface influenced by forest litter principally due to forest litter forcing decrease and T-s increase. The effects of forest litter on the energy budget increased with time and lc. We found that forest litter exerted the most significant impact on K-up arrow and L-up arrow at daytime during the latter stages of the snowmelt period. The influence of forest litter on H was more apparent on windy days. The presence of forest litter increased gains in shortwave radiation and losses in longwave radiation and decreased gains in H. Compared to the simulated energy (K-up arrow + L-up arrow+H) over a snow surface without litter, the calculated energy decreased by -13.4 W/m(2) and increased by 9.0 W/m(2), respectively, at the 20% FCO and 80% FCO sites during the latter stages of the snowmelt period. Overall, forest litter facilitated snow surface energy gains at the 80% FCO site and impeded them at the 20% FCO site during the latter stages of the snowmelt period.