Spatial variation of reference evapotranspiration in Kermanshah province

Document Type : Thechnical Note


Water Engineering Department,, Faculty of Agriculture, Razi University


Due to the spatial variations of evapotranspiration, and lack of adequate point estimations using interpolation methods for spatial analysis is necessary. The aim of this study was to estimate the regional values of reference evapotranspiration (ETo) in Kermanshah province, west of Iran and comparison with Iran National Water Document. For this purpose, daily weather data of 38 meteorological stations of Kermanshah and neighboring provinces were obtained from the Iran Meteorological Organization. Three methods were used for calculation and zoning of ETo, based on Penman and Penman-Monteith equations. In the first and second methods, the meteorological data were interpolated and then ETo was calculated using the interpolated data, while in the third method the point estimation of ETo (weather stations) were interpolated. For the purpose of interpolation, the CGMS software was used in a gridded network of 366 cells with 10 × 10 km size. The results showed that there exist a significant spatial variations ETo across the province. In general, in the western regions of the province, with higher temperature and lower altitude, higher values of ETo was observed. The ETo estimations based on Penman-Monteith method were higher than Penman method. Although the ETo values presented in the Iran National Water Document are calculated by the Penman-Monteith equation, but obtained amount for plain regions of the province are more consistent with Penman- equation estimations.


Main Subjects

Allen, R. G., Pereira, L. S., Raes, D., Smith, M. 1998. Crop evapotranspiration-guidelines for computing crop water requirements- FAO irrigation and drainage paper NO. 56. FAO, Rome.
Baruth, B., Genovese, G., Leo, O. 2007. CGMS version 9.2 user manual and technical documentation. Joint Research Center Scientific and Technical Reports. pp 116.
Beek, E. G. 1991. Spatial interpolation of daily meteorological data. Theoretical evaluation of available techniques. Report 53.1, DLO Winand Staring Centre, Wageningen, The Netherlands, pp 43.
Bolhasani, K., Zarei, H. 2016. Spatial estimation and zoning reference evapotranspiration using geostatistical methods and geographic information system (case study: Bakhtegan Basin). Water Science Engineering, 6 (13): 7-21. (in Farsi (
Boogard, H. L., Diepen, van C. A., Roller, R. P., Cabrera, J. M., Laar van, H.H. 1998. User’s guide for the WOFOST 7.1 crop growth simulation model and WOFOST Control Center 1.5. Technical document 52, Winand Staring Centre for Integrated Land, Soil and Water Research, Wageningen, Netherlands.
Dinpashoh, Y., Babamiri, O. 2020. Trends in reference crop evapotranspiration in Urmia Lake basin, Arabian Journal of Geosciences. 13(372)
Farhadi Bansouleh, B. 2009. Development of a spatial planning support system for agricultural policy formulation related to land and water resources in Borkhar and Meymeh district, Iran. Ph.D. Thesis, ITC/Wageningen University, Enschede/Wageningen, The Netherlands.
Gong, L., Xu, Ch., Chen, D. 2005. Spatial interpolation and analyses of reference evapotranspiration and its temporal trends in Changjiang (Yangtze River) Catchment, China, Geophysical Research Abstracts, 7: 04875.
Hodam, S., Sarkar, S., Marak, A. G., Bandyopadhyay, A., Bhadra, A. 2017. Spatial interpolation of reference evapotranspiration in
india: comparison of IDW and Kriging
methods. Institution of Engineers, 98(4): 511–524.
Malamos, N., Tsirogiannis, I. L., Tegos, A., Efstratiadis, A., Koutsoyiannis, D. 2017. Spatial interpolation of potential evapotranspiration for precision irrigation purposes. In Proceedings of the 10th World Congress on Water Resources and Environment, Athens, Greece.
Mardikis, M.G., Kalives, D. P., Kollias, V. J. 2005. Comparison of interpolation methods for the prediction of reference evapotranspiration- An application in Greece. Water Resources Management, 19(3):251-278.
Niazi, Z. 2015. Evaluation and comparison of different methods of estimating reference evapotranspiration (based on the method of mass transfer) in different climates and its zoning in Iran. M.Sc. Thesis, Water engineering, Razi University, Kermanshah, Iran. (in Farsi (
Pengcheng,T., Bing, X., Delong, T., Jie , R., Zekun, L. 2021. Temporal and spatial variations of meteorological elements and reference crop evapotranspiration in Alpine regions of Tibet, China. Environmental Science and Pollution Research Journal, 1-7.
Penman, H.L. 1948. Natural evaporation from open water, bare soil and grass. Proceedings Royal Society, Series A, 193:120-146.
 Sargordi, F. Farhadi Bansouleh, B.  Sharifi, M.A., Van Keulen, H. 2013. Spatio-temporal variation of wheat and silage maize water requirement using CGMS model. International Journal of Plant Production, 7 (2): 207-223.
Soltani, N. 2015. Evaluation and comparison of different methods of estimating reference evapotranspiration based on methods of evaporation from evaporation pan in Iran and its zoning using GIS. M. Sc. Thesis, Water engineering, Razi University, Kermanshah, Iran. (in Farsi (
Van der Voet, P., van Diepen, C. A., Oude Voshaar, J. 1994. Spatial interpolation of daily meteorological data. A knowledge-based procedure for the regions of the European Communities. Report 53.3, DLO Winand Staring Centre, Wageningen, The Netherlands, pp 105.
Xavier, A. C., King, C. W., Scanlon, B. R. 2016. Daily gridded meteorological variables in Brazil (1980–2013), International Journal of Climatology, 36(6): 2644–2659.