Spatial Estimation and Zoning of Reference Evapotranspiration Using the Geostatistics and Thiessen Method (Case study: Hamadan

Estimation of reference evapotranspiration is one of the important components of water balance in each region and that is one of the effective factors in proper irrigation planning for improving water use efficiency. Among the methods that allow the estimation of variables on a regional scale, two methods of geostatistics and Theissen have key roles for land interpolation in extensive level. This study was conducted in Hamadan province. The best variograms was determined, which were the best fit for the exponential model in Kriging method. In the Theissen method's internal analysis, large values of errors are expanded for those stations located in the north-west and south regions, and the range of error variations is between 0.5% to 16%. But in the Kriging method, these errors are distributed in the north-west and south-west regions, while this method estimated better than Theissen's method, and the range of error variations is between 0% to 12%. Comparison of geostatistics and Theissen interpolation methods showed that in the scale of the seasonal, the geostatistical methods have a higher accuracy, but on an annual scale considering the ease of using the Theissen method, taking into account the accuracy required, there is the possibility of using Theissen's method.