The Evaluation of Two Ways for Preparation Spatial Distribution Maps of Reference Evapotranspiration

Evapotranspiration (ET0) is a basic parameter for determination irrigation program which has to be estimated using interpolation methods due to its spatial variation. A factor which can affect interpolation results is interpolation stages sequence. Current study was conducted to compare two ways for preparation of spatial distribution maps of ET0. In the first way، ET0 was calculated using climatic data and Hargreaves-Samani method in weather stations positions and then were interpolated. In the second way، the Hargreaves-Samani equation components are firstly interpolated and then ET0 maps were produced by proper commands in GIS. So، 10-year climatic data (2001-2010) of 46 stations for preparation the maps and 5 stations as validation stations in Mazandaran province were gathered. The data were interpolated using Ordinary Kriging method and the interpolation error was compared using Root Mean Squared Standardized Error (RMSSE). The results showed that the temperature data has better spatial correlation and lower interpolation error. But for estimation verification، ET0 amounts derived from the two ways were compared to the computed ET0 in validation stations positions and showed that the two ways difference was not significant. So، these two ways have not differences for producing ET0 maps.