[Characteristics of surface energy fluxes over a sparse shrubland ecosystem in the farming-pastoral zone of the Loess Plateau, Northwest China].

Based on the energy flux and meteorological data during 2011-2012 over a sparse shrubland ecosystem in the farming-pastoral zone of the Loess Plateau, this study investigated the diurnal and seasonal variations of the energy balance components, and discussed the responses of the latent and sensible heat fluxes to different intensities of rainfall events. In addition, we identified the major environmental controlling factors on latent and sensible heat fluxes via correlation analysis. The results showed that the diurnal and seasonal variations of net radiation (Rn), sensible heat flux (H), latent heat flux (LE) and soil heat flux (G) all showed single-peak curves. The annual mean values of Rn, H, LE and G were 78.19, 33.32, 24.91 and 2.65 W · m(-2), respectively. The ratios of energy budget components to net radiation were 43% (H/Rn), 32% (LE/Rn), and 3% (G/Rn), which indicated that sensible heat flux was the major form of energy loss at this site. In the growing season, the ratios of sensible heat flux and latent heat flux to net radiation were nearly the same (36%); while in the non-growing season, sensible heat flux accounted for 54% of net radiation. Latent heat flux increased sharply after heavy and weak rainfall events, while sensible heat flux decreased sharply at the same time. Continuous rainfall events would lead to fluctuations in latent and sensible heat fluxes. There were significant correlations between latent heat flux and net radiation, vapor pressure deficit and vegetation parameter, while remarkable correlations were found between sensible heat flux and net radiation, and air temperature gradient.