, Pradeep Kumar

Accurate estimation of potential evapotranspiration is necessary step in water resources management. Recently, the FAO-56 version of Penman-Monteith equation has been established as a standard for calculating reference evapotranspiration (ET0). Still there are different approaches (requiring less data) which estimate ET0 closely to Penman-Monteith method for different climatological conditions. Performance Evaluation of all the approaches on the same basis is prerequisite for selecting an alternative approach in accordance with available data. Therefore, two most popular temperature-based approaches (Hargreaves and Thornthwaite) and two radiation based approaches (Priestley-Taylor and Turc) were used to estimate monthly potential evapotranspiration (ET0) at Pantnagar (Uttarakhand), India. Further, the performance of all these methods were evaluated by regression and error analysis between standard ET0 derived using FAO-56 Penman-Monteith method and ET0 values estimated using all the four methods, on monthly and seasonal basis. On monthly basis Turc method performed best with lowest RMSE (0.562), ARE (0.137), AAD (0.448) and high coefficient of determination (0.792). On seasonal basis, the Priestley-Taylor methodwas found to be the best for Rabiseasonwith lowest error values and minimum seasonal over/under ET0 predication rat