The use of large aperture scintillometer and eddy covariance system for monitoring energy and water vapour fluxes over different surfaces in the Heihe River Basin, China

摘要

We analysed the seasonal variations of energy and water vapour fluxes, with a special focus on evapotranspiration (ET) over various surfaces: irrigated cropland (Yingke, YK), alpine meadow (A'rou, AR), and spruce forest (Guantan, GT). Energy and water vapour fluxes were measured using eddy covariance systems (EC) and a large aperture scintillometer (LAS) in the Heihe River Basin, China, in 2008 and 2009. We also determined the source areas of EC and LAS measurements for each site. The results show that the main EC source area was within a radius of 200 m at all sites. The main source area for the LAS (with a path length of 2390 m) stretched along a path line about 2000 m long and 700 m wide. The ground surface conditions in the source areas changed with season and site, and there were characteristic seasonal variations in energy and water vapour fluxes at all sites. The sensible heat flux was the main term of the energy budget during the dormant season. During the growing season, the latent heat flux dominated the energy budget, and an obvious "oasis effect" was observed at YK. The monthly ET reached its peak in July at YK and June at GT in both 2008 and 2009, while at AR it reached its peak in August in 2008 and June in 2009. ET at AR measured by different scales (kilometres scale, LAS; hundred metre scale, EC) had the similar monthly variations, presenting single peak patterns (appearing in August in 2008). There are also some differences between LAS and EC measurements because of the energy imbalance of EC system, the different source areas and surface heterogeneity.