Comparison of Evaporation Schemes and Methods of Estimation of Class A Pan Coefficient at Tharandt, Germany

Abstract

To find the most accurate evaporation or evapotranspiration estimation method(s) for the summer half-year (April to September) for a very humid temperate region, Tharandt, Germany, the class A pan evaporation ( E p ) found from the water level difference of class A evaporimeter measurement and widely known potential evapotranspiration (PET) estimation methods, namely, Haude, Wendling, and Penman, have been employed. Data representation techniques such as box plot and trend check as well as linear regression model and model evaluation statistics such as R 2 , RMSE, MPE, NSE, MAE, RSR, and p value have been used to compare the estimated values of PET and values of E p with reference evapotranspiration (ET o ) values. ET o was used as the reference method using calibrated values, a s \u2009=\u20090.014 and b s \u2009=\u20090.50, in Angstrom formula. The result showed that all the evaporation schemes had very good correlation with the reference method. The overall ranking shows merits in using Wendling and Penman methods. Moreover, a trial estimate of class A pan coefficient ( K p ) was compared with K p values estimated from the equation of Frevert et al. and Snyder. The empirically estimated trial method gave accurate estimates for fetch distances of 10\xa0m, 20\xa0m, 100\xa0m, and 500\xa0m. Graphical abstract For a very humid temperate region, Tharandt, Germany for the summer half-year, methods of estimation of evaporation, evapotranspiration, and class A pan coefficient ( K p ) were compared. The reference evapotranspiration (ET o ) and K p according to Allen et al. were used as the reference methods. Similarly, K p from the equation of Snyder and Frevert et al. as well as a trial method of estimation of K p were compared using box plots.