关键词: 高寒草甸, 能量交换, 蒸散, 涡动相关, 若尔盖高原, 青藏高原

Abstract: The alpine meadow ecosystems of the Zoige Plateau play important roles in the energy and water cycle of the Qinghai-Tibet Plateau, but observation data of this region regarding to surface energy and water fluxes are very scarce. In this study, annual flux measurements were conducted based on the eddy covariance technique at a typical alpine meadow on the Zoige Plateau by using a three-dimensional sonic anemometer and an infrared open-path carbon dioxide and water vapor analyzer. The surface energy and evapotranspiration (ET) fluxes were calculated at the basis of half-hour. The purpose of this study is to reveal the characteristics and influencing factors of surface energy exchanges and ET. The results are as follows. All energy flux components showed clear diurnal and seasonal variation patterns. The annual mean net radiation, sensible heat, latent heat, and soil heat fluxes were 94.5, 21.0, 51.8 and 1.2Wm−2, respectively. The energy fluxes showed a “single peak” diurnal variation pattern both in the growing season and the non-growing season, despite different peak times for different energy components. During the non-growing season, the sensible heat fluxes were slight larger than the latent heat fluxes, while the latter absolutely dominated during the growing season. The annual mean Bowen ratio and energy closure rate were 0.70 and 0.77, respectively. Radiation was the most important environmental factor that influenced the sensible heat fluxes, while temperature, radiation and water vapor pressure deficit for the latent heat fluxes. The ET fluxes during the growing season were significantly larger than those during the non-growing season. The daily ET fluxes ranged from 0.12 to 5.09mmd−1, and the annual mean value was 1.82mmd−1. Evapotranspiration during the non-growing season is controlled by the surface conductivity; during the growing season it is dominated by the radiation, rather than the surface conductivity of soil and vegetation. On a seasonal scale, the dynamics of ET depended on the seasonal variation of precipitation. The annual accumulated precipitation and ET were 682.7mm and 673.6mm, respectively, of which the growing season accounted for 84% and 82%. The lack of precipitation from June to July constrained the ET fluxes. During this period, soil water storage became the main source of ET. All precipitation finally returned to the atmosphere through ET. In this study, the seasonal variation patterns of the surface energy fluxes and ET were similar to those reported by other measurement studies on the Qinghai-Tibet Plateau. However, the annual mean Bowen ratio and annual accumulated ET were the largest among these studies. Such results were jointly attributed to the effects of temperature, precipitation, surface vegetation and other factors. Data of this study could be used for the parameterization optimization of the land surface models and for the validation of satellite and remote sensing data in the Zoige region.

Key words: Alpine meadow, Energy exchanges, Evapotranspiration, Eddy covariance, Zoige Plateau, Qinghai-Tibet Plateau