Performance of radiation-based reference evapotranspiration equation developed for Indian sub-humid conditions

In this study, asite-specific radiation based equation for estimating reference evapotranspiration (ET-0) was developed and its performance was statistically analysed in comparison to widely accepted FAO Penman-Monteith (FAO-56 PM) model and four radiation-based ET-0 methods for sub-humid Hazaribagh region of Jharkhand state. The equation was developed with daily values of incoming solar radiation in conjunction with air temperature (minimum and maximum) by considering daily FAO-56 PM ET0 values as index with weather dataset of 15 years (1990-2004). The performance of developed equation validated with eight years (2005-2012) daily weather dataset revealed that it estimated E-0 values better than other radiation-based methods. The respective higher and lower values of agreement index and root mean square error with FAO-56 PM ET0 values during validation period confirms efficacy of developed equation whose performance tested at another Indian sub-humid location (Pantnagar) confirmed its suitability as well. Considering the limitations associated with reliability and availability of weather data especially in developing countries, developed equation is recommended as practical one to estimate ET0 in sub-humid climatic conditions if FAO-56 PM model cannot be used due to non-availability of required weather parameters at a location.