Effect of Snow Cover on Water and Heat Transfer in Alpine Meadows in the Source Region of Yellow River

The extreme snowfall events have increased in recent years in the Tibetan Plateau (TP). However, soil water-heat transfer under different snow conditions has rarely been explored in detail. Here, multi-source observational data of five years is analyzed for the influence of snow cover on water-heat transfer in alpine meadows of the source area of the Yellow River. The main results are as follows: The warming rate of deep soil in the yearly cycle was much faster than the cooling rate, which was reversed in shallow soil. Snow cover reduced the average temperature and extreme low temperature events of the shallow soil, whose insulation effect mainly presented in the mid-frozen period, insufficient to offset the heat lost by the high albedo in the early and late frozen periods. In more snow year, the similar thawing dates at different depths of soil, as well as plenty of soil voids due to low ice content and high gravel content, were conducive to snowmelt infiltration and making it pass through the frozen soil layer and arrive on soil at 3.20 m or deeper. The snowmelt greatly increased soil thermal conductivity in May of more snow year. Even if covered with snow cover, the surface air at noon was warmer than the upper layer and there was not a temperature inversion. Except in more snow year, opposite temperature gradients appear in soil around 0.80 m depth in mid-spring, impeding the heat transfer in the vertical direction. In less snow year, the long-term freezing-thawing cycles aggravate the evaporation and loss of surface soil water in spring. Between more and less snow years, the difference in sensible heat flux was much larger than the latent heat flux in winter and early spring. This study will bring to light the snow cover-frozen soil interaction in the TP