Dependency of Evaporation and Class A Pan Coefficient on Meteorological Parameters

 

Abstract

The relation of evaporation deriving meteorological parameters particularly wind speed, solar radiation and vapor pressure deficit with evaporation schemes namely Class A pan evaporation (Ep), potential evapotranspiration (PET) and reference evapotranspiration (ETo) at Tharandt, Germany for the summer half-year of 2004-2013 was investigated. PET was calculated using three methods: 1. Haude (2005), 2. Wendling (1991), 3. Penman (1963); whereas, ETo was calculated according to Food and Agricultural Organization-Penman Monteith method. The results showed that the evaporatin schemes were mainly driven by solar radiation (R2 ≥ 0.69, RMSE ≤ 0.76mm d-1) and vapor pressure deficit (R2 ≥ 0.53, RMSE ≤ 0.92mm d-1). The effect of wind speed at 2m in deriving the evaporation schemes was negligibly small (R2 < 0.12). An equation is derived for estimation of Ep from measured meteorological parameters alone which makes this study special. In another scenario, Class A pan coefficient (Kp) which is the ratio of ETo and Ep had shown good correlation with Ep only (R2 = 0.50, RMSE = 0.19, n = 1483). The correlation of Kp with ETo, shortwave radiation, wind speed at 2m, vapor pressure deficit, relative air humidity, and air temperature was too low (R2 < 0.1).

 

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