Investigating the influences of wind function parameterization on evaporation estimation using the generalized complementary principle

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The complementary principle (CR) is the most practical method for estimating regional evaporation (E) based only on routine meteorological observations. However, CR-based models have certain problems that must be solved for widespread application, such as the influence of wind function types and parameterization. In this study, the generalized CR with polynomial forms (GCR) as a case study is applied to investigate the influences of two different parameterization schemes of wind function—the Penman wind function (fPM) and theoretical wind function (fSM)—on evaporation estimation. The observed daily E values from nine eddy flux stations in Australia with contrasting climates and land cover types were collected to quantify the influences. The results showed that the GCR successfully estimated the E value of flux stations with both the fPM and fSM, and the E value estimated with fSM was more sensitive to wind speed than that with fPM. The estimated aerodynamic term (EA), estimated evaporation error (Eerror), and parameter αc showed marked differences between the two wind functions. The EA-SM (hereafter, subscripts PM and SM represent the wind function type) is approximately 1.05- to 5.06-fold greater than the EA-PM across stations, with a mean of 2.60 ± 1.33 (mean ± standard deviation). The correlation between Eerror-SM with wind speed (u) was positive with an average slope of 0.19, while that of fSM was negative with an average slope of −0.13. The difference in the calibrated parameter of the GCR (i.e., αc) between the two wind functions varied site-to-site, ranging from 0.02 to 0.31. This study highlights that both wind function parameterization schemes successfully estimate regional evaporation, but highly differed in evaporation components, errors, and parameter. These results can help to understand and adopt proper wind parameterization schemes for wider applications of GCR method. Additional studies are required to generalize the spatial variability of different wind function parameters and their influence on the applicability of the GCR.