关键词: 蒸散, 涡度相关法, 波文比, 小型蒸渗仪, 高寒草甸, 疏勒河流域

Abstract:

The evapotranspiration (ET) of alpine meadow ecosystem in the upper reach of the Shulehe River Basin, Northeastern Qinghai-Tibetan Plateau during the main growing season in 2011 was measured using the micro-lysimeter(ML) method, the eddy covariance (EC) technique, and the Bowen Ratio Energy Balance (BREB) method. Results showed that the turbulent fluxes measured by EC and available fluxes measured by BREB system were imbalanced. The energy balance ratio (EBR) was 0.84. The reasons were as follows: non-synchronization of fluxes, low closure degree in nighttime and the effect of precipitation. The evapotranspiration values that estimated by BREB, ML and EC were 270.6 mm, 238.9 mm and 236.1 mm, respectively. Significant correlation existed between the evapotranspiration measured by the three methods. The determination of evapotranspiration by EC system was lower than the BREB system as many similar findings indicated. The presence of vertical diffusion and convection resulted in the underestimation of latent heat flux in EC systems was the main reason. Though the evapotranspiration results estimated by EC method and ML method were very close, the diurnal variations were not entirely consistent. According to the local natural conditions of soil and hydrology, water for evapotranspiration originated from the precipitation in the observation station. During the observation period, there was nearly no soil water storage and surface runoff. In addition, the vegetation growth was in good condition. Deduced by those facts, the value of evapotranspiration should be equal to that of precipitation, i.e. about 250 mm. From this point, the evapotranspiration values estimated by the three methods were within a reliable range. The results suggested that the evapotranspiration may be underestimated by EC while overestimated by BREB. Although EC method might underestimate evapotranspiration due to the underestimation of latent heat flux, the evapotranspiration could be obtained directly and the continuous long-term site observation could be realized either. Also, the obtained results of evapotranspiration could represent the average moisture exchange rate between the land surface and the atmosphere in a certain area. Furthermore, the EC system could also be used for the determination of CO₂ flux in the prairie region. Considering the estimation precision and data continuity, the eddy covariance method had advantages over the other two methods and had more application perspective in an alpine meadow area as the upper reach of the Shulehe River Basin.

Key words: evapotranspiration, eddy covariance, Bowen Ratio Energy Balance, micro-lysimeter, alpine meadow, the Shulehe River Basin