Temporal upscaling of instantaneous evapotranspiration from the reference evaporative fraction method with fixed and variable canopy resistances

Surface evaopotranspiration (ET) is one of the significant water and energy components in the land and atmosphere system. Remote sensing technology provides opportunity to map surface ET at large heterogeneous area. However, this ET is generally produced at the instantaneous scale. This paper investigated in the constant reference evaporative fraction upscaling method whether the use of a variable canopy resistance in the reference ET estimation from the Penman-Monteith equation could improve the daily ET estimate. Near-surface meteorological variables and eddy covariance system measurements used as the model inputs and ground-truth were collected from late April 2009 to late October 2011 at the Yucheng station in Northern China. Preliminary results showed that it was not an imperative step to use a more complex parameterization of canopy resistance to estimate the reference ET when the constant evaporative fraction method was applied to upscale the instantaneous ET to daily value.