资源环境科技发展态势分析平台

Observing the isotopic evolution of snow meltwater helps understanding the process of snow melting, but remains a challenge to acquire in the field. In this study, we monitored the melting of two snowpacks near Baishui Glacier No. 1, a typical temperate glacier on the southeastern Tibetan Plateau. We employed a physically‐based isotope model (PBIM) to calculate the isotopic composition of meltwater draining from natural snowpacks. The initial condition of PBIM was revised to account for natural conditions, i.e. the initial δ¹⁸O stratigraphy of snow layers before melting. Simulations revealed that the initial heterogeneity of δ¹⁸O in snow layers as well as ice‐liquid isotopic exchange were responsible for most variations of δ¹⁸O in snow meltwater, whereas new snow and wind drift could result in sudden changes of the isotopic composition of the meltwater. The fraction of ice involved in the isotopic exchange (f) was the most sensitive parameter for the model output. The initial δ¹⁸O in the snowpack is mirrored in meltwater in case of small f and is smoothed with a large exchange fraction f. The other unknown parameter of PBIM is the dimensionless rate constant of isotopic exchange, which depends on water percolation and initial snow depth. The successful application of PBIM in the field might not only be useful for understanding snow melting processes, but might also provide the possibility of predicting the isotopic composition of snow meltwater and improve the accuracy of hydrograph separation.