Characteristics of the Surface Turbulent Fluxes over Degraded Grassland and Cropland in the Semi-Arid Area

The seasonal and diurnal variations of the surface turbulent fluxes over the degraded grassland and the cropland are investigated,based on the turbulent flux data measured with Eddy Covariance(EC)method and radiation and meteorological data collected from 2003 to 2005 in the semi-arid area.The influence of different meteorological backgrounds on the turbulent fluxes between land and atmosphere over different land surfaces is also discussed.It is shown that there are clear seasonal and diurnal variations for the components of surface energy balance over the degraded grassland and the cropland in the semi-arid area.The interannual variability of the components of surface energy balance is mainly influenced by meteorological backgrounds in the same year,especially by precipitation.The ratios of net radiation to latent heat flux and to sensible heat flux show an opposite phase change over both degraded grassland and cropland,and the ratio for the latent heat flux is higher than that for the sensible heat flux in summer.The trends of mean monthly Bowen ratios over two types of underlying surfaces are almost the same,and the magnitudes of the Bowen ratios are near.The Bowen ratio in summer is not larger than 1.0 over both degraded grassland and cropland.