Effects of spatial variability on estimation of evapotranspiration in the continental river basin

Water and energy balance models were developed at the local and basin scale by aggregating a HYDRUS Model across scales in a topographic framework. A spatially distributed approach was followed to aggregate the HYDRUS Model to basin scale. The effects of spatial variability on the estimation of evapotranspiration at basin scale are emphatically discussed. In the present work the main emphasis was focused on the estimation of the spatial variability of both evapotranspiration and the calculation of statistical parameters of soil water storage from local scale to basin scale. Our results illustrate that the changes of the local and area-averaged potential evapotranspiration (ETp), actual evapotranspiration (ET) show a strong seasonal trend where the mean and standard deviation (STD) approximately fit the two-harmonics of Fourier series. Moreover, ETp and ET are random variables which follow the normal distribution with mean and deviation changing with season. A sensitivity analysis of the results shows that to a reasonable degree, the incorporated model can be used to determine the relationship between the actual area-averaged evapotranspiration and the main controlling factors for both bare soil and vegetated surfaces.