Evaluation of the accuracy of different combined methods for estimating the potential evapotranspiration in different climates (case study: Iran)

Document Type : Research Paper


1 Ph.D. Candidate, Department of Water Engineering, Campus of Agriculture and Natural Resources, Razi University, Kermanshah, Iran

2 Professor, Department of Water Engineering, Campus of Agriculture and Natural Resources, Razi University, Kermanshah, Iran

3 Assistant Professor, Department of Water Engineering, Campus of Agriculture and Natural Resources, Razi University, Kermanshah, Iran


Estimating the exact value of reference evapotranspiration is very important in irrigation planning and determining the irrigation frequency. There are different methods for estimating the reference crop evapotranspiration. The aim of this study was to find the best combined method for estimating the reference evapotranspiration in arid, semi-arid, semi-humid and humid climates of Iran. In this study, based on different necessary data from first order weather stations in the period of 1995 to 2014, the reference evapotranspiration was calculated by some combined methods and compared with FAO 56 Penman Monteith method. The results showed that all methods except Businger and Van bavel method have a good correlation with FAO 56 Penman Monteith (R^2 > 0.96). The accuracy of Businger and Van bavel methods in all regions were low with RMSE and MAE values greater than 0.9 and 0.55 mm per day, respectively. In arid, humid and semi-humid regions of Iran, Penman 1948 and Penman Wright 1972 methods with RMSE and MAE values less than 0.39 mm per day and in semi- arid regions of Iran Penman Wright 1972 methods and Penman 1948 with RMSE and MAE values less than 0.35 mm per day had the highest accuracy.


1. Alizadeh, A., Kamali, G., Khanjani, M.J. & Rahnavard, M.R. (2004). Evaluation of evapotranspiration estimation methods in arid regions of Iran. Iranian Journal of Geographical Research, 19(2), 97-105. (In Persian).
2. Al-Omran, A., Al-Ghobari, H. & Alazba, A. (2004). Determination of evapotranspiration of tomato and squash. International Agricultural Engineering Journal, 13(142), 27-36.
3. Alblewi, B.H. (2012). Assessment of Evapotranspiration Models under Hyper Arid Environments. Msc Thesis, Guelph, Ontario, Canada.
4. Allen, R.G., Jensen, M.E., Wright, J.L. & Burman, R.D. (1989). Operational estimates of reference evapotranspiration. Agronomy journal, 81(4), 650-662.
5. Allen, R.G., Pereira, L.S., Raes, D. & Smith, M. (1998). Crop evapotranspiration-Guidelines for computing crop water requirements-FAO Irrigation and drainage paper 56. Fao, Rome, 300(9), D05109.
6. Babamiri, O. & Dinpazhoh, Y. (2016). Comparison and evaluation of twenty methods for estimating reference evapotranspiration based on three general categories: air temperature, solar radiation and mass transfer in the basin of lake urmia. Iranian Journal of Water and Soil Sci, 20(77), 145-161. (In Persian).
7. Berti, A., Tardivo, G., Chiaudani, A., Rech, F. & Borin, M. (2014). Assessing reference evapotranspiration by the Hargreaves method in north-eastern Italy. Agricultural Water Management, 140, 20-25.
8. de Sousa Lima, J.R., Antonino, A.C.D., de Souza, E.S., Hammecker, C., Montenegro, S.M.G.L. & de Oliveira Lira, C.A.B. (2013). Calibration of Hargreaves-Samani equation for estimating reference evapotranspiration in sub-humid region of Brazil. Journal of Water Resource and Protection, 5(12A), 1-5.
9. DehghaniSanij, H., Yamamoto, T. & Rasiah, V. (2004). Assessment of evapotranspiration estimation models for use in semi-arid environments. Agricultural Water Management, 64(2), 91-106.
10. Djaman, K., Balde, A.B., Sow, A., Muller, B., Irmak, S., N’Diaye, M.K., Manneh, B., Moukoumbi, Y.D., Futakuchi, K. & Saito, K. (2015). Evaluation of sixteen reference evapotranspiration methods under sahelian conditions in the Senegal River Valley. Journal of Hydrology: regional studies, 3, 139-159.
11. Gao, F., Feng, G., Ouyang, Y., Wang, H., Fisher, D., Adeli, A. & Jenkins, J. (2017). Evaluation of reference evapotranspiration methods in arid, semiarid, and humid regions. JAWRA Journal of the American Water Resources Association, 53(4), 791-808.
12. Ghamarnia, H., Mousabeyg, F., Amiri, S. & Amirkhani, D. (2015). Evaluation of a few evapotranspiration models using lysimetric measurements in a semi-arid climate region. International Journal of Plant & Soil Science, 5(2), 100-109.
13. Khatua, R. & Pasupalak, S. (2018). Comparison of methods for estimation of reference evapotranspiration in North-Central Plateau zone of Odisha. Indian Journal of Agricultural Research, 52(2), 187-190.
14. Lascano, R.J. & Evett, S.R. (2007). Experimental verification of a recursive method to calculate evapotranspiration. Proceedings of the 28th annual international irrigation show, 687-705.
15. McVicar, T.R., Roderick, M.L., Donohue, R.J., Li, L.T., Van Niel, T.G., Thomas, A., Grieser, J., Jhajharia, D., Himri, Y. & Mahowald, N.M. (2012). Global review and synthesis of trends in observed terrestrial near-surface wind speeds: Implications for evaporation. Journal of hydrology, 416, 182-205.
16. Mohammad, F.S. (1997). Calibration of reference evapotranspiration equations for alfalfa under arid climatic conditions. journal of king saud university agricultural sciences, 9(1), 39-56.
17. Moradi, A., Babaei, H., Alimohamadi, A. & Radiom, S. (2020). Estimation of crop coefficients in the Moghan cultivation industry and the study of relationship between evapotranspiration and yield performance. Journal of Iranian Remote Sensing & GIS, 11(4),11-28. (In Persian).
18. Pandey, V., Pandey, P.K. & Mahanta, A.P. (2014). Calibration and performance verification of Hargreaves Samani equation in a humid region. Irrigation and drainage, 63(5), 659-667.
19. Rahimi Khoob, A., Behbahani, S.M.R. & Nazarifar, M.H. (2006). Evaluation of using minimum meteorological  data for Penman Montieth equation- case study Khuzestan province. Iranian Journal of  Agricultural scirnces, 12(3), 591-600. (In Persian).
20. Sharifan, H., Ghahraman, B., Alizadeh, A. & Mirlatifi, S.M.(2006). Comparison of different methods for estimating reference evapotranspiration (combined and temperature) by the standard method and investigating the effects of air drought on it. Iranian Journal of Agricultural Sciences and Natural Resources, 13(1), 19-30. (In Persian).
21. Sentelhas, P.C., Gillespie, T.J. & Santos, E.A. (2010). Evaluation of FAO Penman–Monteith and alternative methods for estimating reference evapotranspiration with missing data in Southern Ontario, Canada. Agricultural Water Management, 97(5), 635-644.
22. Tabari, H., Grismer, M.E. & Trajkovic, S. (2013). Comparative analysis of 31 reference evapotranspiration methods under humid conditions. Irrigation Science, 31(2), 107-117.
23. Temesgen, B., Eching, S., Davidoff, B. & Frame, K. (2005). Comparison of some reference evapotranspiration equations for California. Journal of Irrigation and Drainage Engineering, 131(1), 73-84.
24. Upadhyaya, A. (2006). Comparison of Different Methods to Estimate Mean Daily Evapotranspiration from Weekly Data at Patna, India Irrigation Drainage Systems Engineering, 5, 1-7.
25. Valipour, M. (2014). Assessment of different equations to estimate potential evapotranspiration versus FAO Penman Monteith method. Acta Advanced in Agricaltural Science, 2, 14-27.
26. Yoder, R., Odhiambo, L.O. & Wright, W.C. (2005). Evaluation of methods for estimating daily reference crop evapotranspiration at a site in the humid southeast United States. Applied engineering in agriculture, 21(2), 197-202.
27. Yuanshi, G. (1995). Comparison of the Reference Evapotranspiration Estimated by the Penman-Monteith and FAO-PPP-17 Penman Methods [J]. Acta Agriculturae Universitatis Pekinensis 1.