Features of land surface process over wetland at Tibetan Plateau during soil freezing and thawing periods

Using observed data at Longbao wetland, Yushu from July 2015 to July 2016, features of soil temperature, soil moisture and surface energy budget were analyzed. The results show that the frozen period of soils lasts from preceding December to subsequent April. The soils at deeper depths freeze later than that near the surface. The thawing process is faster than the freezing process. The soil at 5-40 cm depth completely freezes within 51 d and thaws within 19 d. The magnitude of annual variability of soil water content is up to 0.6 m³/m³. 5-40 cm soil moisture decreases during the freezing period and 5-10 cm soil moisture increases during the thawing period. When the soil is frozen, sensible heat flux increases while latent heat flux decreases during the daytime, net radiation and soil heat flux both decrease, and the diurnal variation of soil heat flux becomes larger. After thawing, latent heat flux, net radiation and soil heat flux all increase during the daytime. Surface albedo, the Bowen ratio, and the thermal conductivity and diffusivity of soil increase after freezing and decrease after thawing. The soil thermal capacity decreases after freezing and increases after thawing.