Quantitative effect of topography and forest type on snow melting process in spring

Snow melting is a main source of river flow and contributes to diminishing drought in spring time in cold regions of northern China. The fact that forest can delay snowmelt runoff has been well known; however, tempo-spatial heterogeneity of snow melting resulted from topography and vegetation still remains unclear. In addition, quantitative estimation of the effect of vegetation and topography on snow ablation would improve the accuracy of watershed hydrology model. In this study, the method of MTCLIM(Mountain microclimate simulation model)was used to calculate or simulate snow evaporation and influence of topography on radiation, the degree day approach modified by topography and vegetation was used to calculate or simulate snow melting rate. The results showed that simulation can reflect the integrated influence of topography and vegetation on snowmelt just as the correlation coefficient of simulation and observation was 0.90. Furthermore, the effect of vegetation on snow melting was greater than that of topography, specifically, regardless of topography, the average snow ablation rate of the entire watershed was 1.26 mm/d which was only 64.6% of that of open plain (1.95 mm/d). However, topography accordingly resulted in a mean snow ablation rate of 1.91 mm/d, almost equal to that of open plain. It should also be noted that simulation accuracy related to specific site still need be enhanced. Snow evaporation cannot be simulated by Priestly-Taylor method based on topography and vegetation, and other factors such as wind need to be taken into account.