Characteristics of Water and Heat Exchanges and Their Crucial Influencing Factors on the Alpine Wetland during the Warm Season in the Source Region of the Yellow River

Wetland is a natural complex of land and water, which has important functions in ecology, hydrology and biogeochemistry. The alpine wetland in the source region of the Yellow River (SRYR) is a key water conservation area of the Yellow River, and it is important to understand the characteristics of water and heat exchanges and their crucial influencing factors in this region. In this paper, the characteristics of water and heat exchanges are analyzed using the field observation data provided by Maduo Climate and Environment Monitoring Labotory of Nothwest Institute of Eco-Environment and Resources, CAS (Chinese Academy of Sciences) for June-August 2014 over the alpine wetland in the SRYR. The Community Land Model (CLM) is applied to simulate heat flux. A roughness length scheme, which aims at the alpine wetland, is designed based on the simulation results. The main results are as follows:(1) The upward and downward short-wave radiation and net radiation fluxes in the warm season have similar diurnal variation patterns, and the diurnal fluctuations of the upward and downward long-wave radiation fluxes are small. The increase in surface temperature lags the increases in downward shortwave radiation flux, and the latent heat flux is always positive and greater than the sensible heat flux. (2) The soil layer in which temperature has significant changes is the top shallow layer in 0-20 cm depth, where there exists an obvious diurnal cycle of temperature variation. The soil temperature starts increasing when heat is transferred down to 5 cm depth at 0900 BJT (Beijing time), and the heat reaches 10 cm depth at 1100 BJT and 20 cm depth at 1300 BJT. Soil temperature starts decreasing because of the upward transfer of heat after 1800 BJT. The soil layer below 40 cm is hardly influenced by the radiation flux, and the general characteristics of heat transfer is from the shallow top layer to deep layers. (3) The diurnal variation of soil moisture is small, and the soil at 5 cm and 10 cm depths have the minimum and maximum moisture content, respectively. (4) The roughness length for momentum (Z_0m) over the alpine wetland in Maduo during the warm season is stable, which can be set to be a constant Z_0m=0.0143 m. (5) The newly added damping kB^-1 schemes are designed for local alpine wetland, which have a better performance in simulating the surface heat flux than the original scheme of CLM. All these results have significant contributions to the research of land surface process over the wetland.