Evaluation of pan coefficient methods for estimating FAO-56 reference crop evapotranspiration in a semi-arid environment

Abstract

Five empirical methods (viz. Cuenca, 1989; Snyder, 1992; Orang, 1998; Pereira, 1995 and Allen and Pruit, 1991) were evaluated to find out Kp using daily weather data (temperature, relative humidity and wind speed) of Indian Agricultural Research Institute station over the years 1997 to 2011. It was observed that the measured Kp values showed bi-modal variation during the year with values ranging between 0.72 to 0.93, being lower in the summer months and higher in rainy and winter months. Out of the five methods, Snyder method was found to be the best for estimating Kp with RMSE of 0.05, and MAD of 0.04. The ETo estimated with Kp of Snyder method also showed lowest RMSE of 0.19, and MAD about 0.16. It is recommended that temporal variation in Kp should be computed for each station for estimation of ETo and Snyder method is recommended for estimating Kp in semi-arid environments.