Abstract: The air temperature, relatively humidity, wind speed, shortwave and longwave radiation beneath forest with different canopy openness were recorded by automatic weather station, the snowmelt rate was measured by snow lysimeter. The energy budget on snow surface was calculated according to these meteorological factors beneath forest. This paper mainly analyzed the characteristics of the snow ablation process, and how the energy budget influence the snow ablation process beneath forest with different canopy openness. The results showed the differences of snow ablation process beneath forest with different canopy openness were decided by the snow equivalent water content and energy budget on snow surface. The snow depth beneath forest with different canopy openness have the same changing tendency. The bigger the canopy openness was, the shallower the snow depth was, the longer the duration of snowmelt period was. The snowmelt rates beneath forest with different canopy openness was increased with time. The beginning and the end time of forest snow melt was 20~30 days later than snow melt on sunny slope. In the early snowmelt period, the larger the canopy openness was, the higher the snowmelt rates was, but the relationships between forest snowmelt rate and canopy openness in late snowmelt period was contrary to that on early snowmelt period. The snowmelt rates beneath different canopy openness have the similar daily variation. The daily variation of snowmelt rate showed the shape of single peak type in the clear day, and the curve was similar to positive skewness distribution. The variation of snowmelt rate in precipitation was mainly affected by the precipitation form, amount of precipitation, snow depth and other physical property of snow. Due to the difference of energy budget and physical property of snow beneath forest with different canopy openness between different snowmelt period, the snowmelt rate and the daily variation of snowmelt rate beneath forest with different canopy openness was different. The forest snowmelt rate and daily variation of snowmelt rate were decided by net shortwave and longwave radiation. The net radiation was the main energy source for forest snowmelt, the sensible and latent heat flux were not as important as on the sunny slope. Due to the shortwave and longwave radiation on snow surface beneath forest were more complex than on the sunny slope, the air temperature can not indicate the differences of the shortwave and longwave radiation beneath forest with different canopy openness, the simulating of snowmelt runoff should be based on the process of mass and energy balance. This paper also showed that the forest snowmelt runoff may be changed through reasonable managements for forest. However, the observed and analyzed forest snow ablation process only based on a single station, in future, we should focous on the larger temporal and spatial scales to observe and analyze energy budget on forest snow surface and snow ablation.

Key words: snowmelt period, forest snow, snow depth, snowmelt rate, energy budget