Nonlinear advection‐aridity method for landscape evaporation and its application during the growing season in the southern Loess Plateau of the Yellow River basin

The advection‐aridity approach to estimate actual evaporation from natural land surfaces is one of the better known implementations of Bouchet's complementary principle. Detailed measurements at 2, 12, and 32 m above the ground surface during the growing seasons of 2004–2007 allowed validation of a generalized nonlinear form of this approach above the highly variable terrain in Changwu County in the southern Loess Plateau of the Yellow River basin in China. The obtained values of the parameters were found to lie well within the ranges to be expected on physical grounds or from previous measurements by different experimental means; calibration on the basis of any one year of data allowed predictions within roughly 5% on average. Relative to the corresponding observed turbulent vapor fluxes, the evaporation rates calculated with measurements at the highest level of 32 m displayed the least scatter but only slightly less than those calculated with measurements at the lower level of 12 m; however, those based on measurements at the lowest level of 2 m displayed considerably more scatter than those derived at the two higher levels. This is consistent with the existence of a blending height at higher elevations above the ground, where the effects of surface variability tend to fade away.