Evaluation of FAO-56 Penman-Monteith and Temperature Based Models in Estimating Reference Evapotranspiration Using Complete and Limited Data, Application to Nigeria
Accurate determination of reference evapotranspiration is very essential for precise computation of crop water use. Several models have been used in computing reference evapotranspiration and they require local calibration in order to validate their usage. Climatic data used in computing reference evapotranspiration (ETo) for Abeokuta, Ijebu-Ode and Itoikin were obtained from Nigerian Meteorological Station (NIMET), Lagos Nigeria. For Abeokuta, complete climatic data were used in the computation of the ETo while limited climatic data were used in computing ETo for Ijebu-Ode and Itoikin using FAO-56 Penman-Monteith (FAO-56 PM), Jensen-Haise and Hargreaves models. In Abeokuta, the average coefficients of determination R2 obtained when ETo computed using Jensen-Haise and Hargreaves models were compared with FAO-56 PM model were 0.7914 and 0.5158 respectively. The average Root Mean Square Errors (RMSEs) obtained between Jensen-Haise, Hargreaves and FAO-56 PM models were 1.03 and 1.79 mmd-1 respectively. The index of agreement between pan evaporation and FAO-56 PM, Jensen-Haise and Hargreaves models were 0.56, 0.71 and 0.52 respectively. The average R2 of the ETo computed using and temperature for FAO-56 PM and Jensen-Haise were 0.6784 and 0.8488 respectively. For Ijebu-Ode, the average R2 when Jensen-Haise, Hargreaves were compared with FAO-56 PM model were 0.9908, 0.9907 respectively. The average RMSEs between FAO-56 PM, Jensen-Haise and Hargreaves were 2.51 and 0.87 mmd-1 respectively while the index of agreement between FAO-56 PM, Jensen-Haise and Hargreaves models were 0.49, 0.88 and 0.54 respectively. Similarly for Itoikin, the average R2 obtained when Jensen-Haise and Hargreaves model were compared with FAO-56 PM were 0.9754 and 0.9557 respectively. The average RMSEs obtained between FAO-56 PM and Jensen-Haise and Hargreaves models were 2.50 and 0.89 mmd-1 respectively while the index of agreement between pan evaporation and FAO-56PM, Jensen-Haise and Hargreaves models were 0.28, 0.61 and 0.34 respectively. It is hereby recommended that beside FAO-56PM model, Jensen-Haise model is also recommended for the computation of ETo in situations where only maximum and minimum temperatures are available in Ogun-Osun River basin.