Suitability Analysis of the Calculation Formulas for Monthly Potential Evapotranspiration in Different Climatic Zones

Evapotranspiration plays a significant role for the redistribution of water on the earth and is a major determination variable in water cycles. A comparison among different evapotranspiration estimating approaches in humid, semi-humid, semi-arid and arid zones is made to analyze their suitability on correlation coefficients between calculated and measured evapotranspiration from Φ20 pan. If the calculated evapotranspiration by Penman-Monteith formula is used as a reference value, we can obtain the conversion coefficient of the potential evapotranspiration from the evaporation of Φ20 pan. Therefore, this analysis is not only very useful for estimation of hydrological balance and water resources, but also significant for impact study of climate changes.