Measurements of Evapotranspiration by Eddy Covariance System in the Hai River Basin

摘要

The eddy covariance (EC) system can measure energy and water exchange between surface and atmosphere directly, which is used widely in the world. Three sites with long-term EC system observations are chosen over different surfaces in the Hai River Basin, namely, Miyun site, Guantao site and Daxing site. Significant diurnal and seasonal variations of water and heat flux were observed in the Hai River Basin. Sensible heat flux varied throughout the years at all sites, with double peak at Miyun site, triple peak at Guantao and Daxing sites, however, latent heat flux presented single peak at Miyun site, with the peak value appears in July to August, and double peak at Guantao and Daxing sites. The analysis shows that the diversity of water and heat fluxes determines the different characteristics of ET among these sites. The Bowen-ratio closure method was adopted to correct the energy imbalance. The annual ET is 582.1mm, 650mm and 515.6mm for Miyun, Daxing and Guantao site in 2008, respectively.