Comparison of Simplified Pan-Based Equations for Estimating Reference Evapotranspiration

Accurate estimation of reference evapotranspiration $\left({\text{ET}}_0\right)$ is essential for irrigation practice. Conversion from pan evaporation data to reference evapotranspiration is commonly practiced. The objective of this study was to evaluate the reliability of simplified pan-based approaches for estimating ${\text{ET}}_0$ directly that do not require the data of relative humidity and wind speed. In this study, three pan-based (FAO-24 pan, Snyder ${\text{ET}}_0$ , and Ghare ${\text{ET}}_0$ ) equations were compared against lysimeter measurements of grass evapotranspiration using daily data from Policoro, Italy. Based on summary statistics, the Snyder ${\text{ET}}_0$ equation ranked first with the lowest RMSE value $\left(0.449\text{mm}{\text{day}}^{-1}\right)$ . The pan-based equations were additional tested using mean daily data collected in Novi Sad, Serbia. The Snyder ${\text{ET}}_0$ equation best matched ${\text{ET}}_0$ estimates by Penman-Monteith equation at Novi Sad with lowest root mean square error value of $0.288\text{mm}{\text{day}}^{-1}$ . The obtained results demonstrate that simplified pan-based equations can be successful alternative to FAO-56 Penman-Monteith equation for estimating reference evapotranspiration. The overall results recommended Snyder ${\text{ET}}_0$ equation for pan evaporation to evapotranspiration conversions. The Snyder ${\text{ET}}_0$ equation consistently provides better results compared to FAO-24 pan equation, although required measurements of only one weather parameter pan evaporation.