Abstract:
Numerous studies have already shown that the Penman-Monteith equation is the most reliable method of evapotranspiration estimation when necessary weather and vegetation data are available, these inputs are difficult and expensive to obtain for many locations in developing countries like India. In such circumstances, radiation based methods or temperature based methods may constitute often the only alternative for the evaluation of ET0. Therefore, reliability of temperature based approaches (Hargreaves-Samani and Thornthwaite) and radiation based approaches (Priestley-Taylor and Turc) in the estimation of ET:, is tested in the present study. These methods alongwith Penman-Monteith method are used to estimate monthly potential evapotranspiration (ET0) at Pantnagar (Uttarakhand), India. The measured values of potential evapotranspiration are selected as the standard of comparison for evaluating these methods. Regression performed between observed and estimated values of ET0 suggested that mean monthly correction factors instead of single local correction factor need to be introduced for improving the performance of these methods. Mean monthly correction factors are then developed and incorporated. The results indicate that ET0 estimates using corrected Hargreaves and Turc methods are well correlated with measured ET0 with coefficient of determination (R2) greater than 0.96. If radiation, humidity and wind-speed data are not available, either the Hargreaves or Turc method with mean monthly correction factors for the study region can be utilized for reliable estimation of ET0.
