Estimation of reference crop evapotranspiration by Chinese pan

The reference crop evapotranspiration is a key parameter for soil-plantation-atmosphere transfer system models, which influence the application of models and the precision of prediction. The 20 cm Chinese pan coefficient Kp was presented according to meteorological data from 65 climatic stations in the Loess Plateau from 1971 to 2000 and the reference crop evapotranspiration calculated by Penman-Monteith equation serves as a standard. Results show that the Kp estimated by relative humidity and wind speed can be used to compute ET₀ combined with observed data from 20 cm Chinese pan. There is a satisfactory correlation between ET₀ of 20 cm Chinese pan and Penman-Monteith method over three or more days. However, the Chinese pan coefficient is very dependent on local climate, and it should be determined by comparing the history data or nearby meteorological station data with the Penman-Monteith. Chinese pan can be used for calculating reference crop evapotranspiration in the Loess Plateau.