Estimating forest evapotranspiration in South China using MODIS data

The evapotranspiration of forestland surface was estimated using MODIS data. The study area is located in Jiangxi province, south China, dominated by tall indeciduous conifers. The parameters of land surface energy balance, i.e., leaf area index (LAI), land surface temperature (LST), surface albedo etc. were inversed from VIS/NIR and TIR band data of MODIS sensor. Some of the assistant data, such as meteorological factors and canopy structure parameters were obtained in-situ at Qianyanzhou ecological experiment station, which is one of the sites in the ecology observation system of Chinese Academy of Sciences. The radiation components and net radiation of surface were estimated with these parameters and ancillary data. Soil heat flux was estimated as a fraction of net radiation from the area coverage of the canopy. Surface sensible heat flux was decided according to surface temperature gradient and aerodynamic resistance. The excess-resistance for scalar flux transfer was also considered. Eventually, the latent heat flux (instantaneous evaporation rate) was obtained as the residual term of the surface energy balance equation. Daily evapotranspiration was then derived from the one-time-of-day estimation.