Spatial Analysis of Water Productivity Index at Major Wheat Production Centers of IRAN

Water resource deficiency and the necessity of sustainable production in irrigated lands have attracted much attention to water productivity issues. In this regard, analysis, estimation, and preparation of water productivity map are necessary as an influential factor to recognize cultivation potential in irrigated lands. The aim of this study was to select a proper interpolation method for water productivity and investigate spatial changes in water productivity in Iranian wheat production centers. In this research, 241 field data were used, of which range of water productivity (irrigation water + effective precipitation) was estimated between 0.3 to 2.58 kg.m-3 with the average of 0.79 kg m-3, in 2016-2017 season. Interpolation methods used included Ordinary Kriging, Inverse Distance Method (IDW), and Radial Basis Function (RBF). Cross Validation technic was applied to evaluate methods by statistical measures such as Root Mean Square Error (RMSE), Mean Bias Error (MBE), and Mean Absolute Relative Error (MARE). Interpolation methods evaluation showed that between available procedures, typical Kriging method with exponential semi-variogram model had the most proper condition to prepare wheat water productivity zoning map. The results of the spatial analysis of water productivity confirmed that geostatistics could be used with acceptable accuracy (MBE=0.005) to provide water productivity mapping. Results of Cluster analysis of the effective factors (salinity of irrigation water, soil salinity, and crop cultivar) on wheat water productivity index showed that the areas suitable for wheat cultivation were separated into 13 independent groups (at the 5 percent level), such that the highest and lowest mean water productivity of wheat were observed in group 5 (Mean = 0.84 kg.m-3) and group 10 (Mean = 0.41 kg.m-3), respectively.