Inter-comparison of radiation -based reference crop evapotranspiration methods

Abstract

This paper investigates the evaluation and inter comparison of evapotranspiration models with data from a station in Tamil Nadu, India. In the present study cross comparison of the best or representative equation forms selected from each category namely (1) temperature-based methods, and (2) radiation-based methods ware made along with FAO Modified Penman method. Six representative empirical ETr equation selected from the two categories, namely Blaney-Criddly, Hamon, and Kharrufa (temperature-based), Doorenbos and Puitt, Jensen-Haise, and McGuinness and Bordne (radiation-based) were evaluated and compared. All the equations are recalibrated and the constants in each equation are redefined for the data from the selected station. The result shows that, large bias existed when the original constants were used for the determination of ETr. Regression equations were developed to correct the differences in magnitude of evapotranspiration. When recalibrated constant values were substituted for the original constant values, all the six methods have improved in the estimation of the ETr for the region. Based on the closeness in ETr value to that of FAO Modified Penman method and r2 value, radiation-based methods namely Doorenbos-Pruitt and Jensen-Haise can be recommended for estimating ETr in the study area than using temperature-based methods.