Evapotranspiration in Summer on the permafrost area on the North Side of the Tanggula Mountains, the Tibetan Plateau

This study emphasized the role of vegetation in land surface processes occurring on the permafrost area on the Tibetan Plateau. In order to understand the effect of vegetation in the energy and water cycle of the permafrost area, albedo on various surface conditions was measured in the north side of the Tanggula Mountains. In addition, evaporation and transpiration were measured by using micro-lysimeters. The surface conditions of five micro-lysimeters were water, bare soil, grass with natural moisture soil, grass with saturated soil, and grass with surface-sealed soil, respectively. The effect of surface conditions was evaluated as surface moisture availability in the bulk transfer equation. Albedo of the permafrost area without snow cover in summer can be estimated as the weighing average of the area ratios of grass, dry soil and wet soil. The albedo at the study site is 0.176. The surface moisture availability of grass with surface-sealed soil decreased with the increase of the vapor pressure difference between leaves and atmosphere. The evapotranspiration of grass with saturated soil is divided into evaporation from wet leaves, transpiration and evaporation from soil surface in terms of surface moisture availabilities. The surface availability of wet leaves ranges from 1.0 to 0.75. The maximum of the surface moisture availability of grass with saturated soil is 0.75, including the contribution of the surface moisture availability, that is 0.18.