The reference evapotranspiration (ET0) is an essential variable in the agrohydrological systems and its estimation on a regional scale is limited to its spatial variability. This study compares two approaches for preparation of spatial distribution maps of ET0 in Mazandaran province of Iran. In the first approach, ET0 was calculated using climatic data and Hargreaves-Samani equation in weather stations locations and then were interpolated. In the second approach, the components of the Hargreaves-Samani equation were interpolated and then ET0 maps were prepared by applying the Hargreaves-Samani equation and suitable commands in GIS. The 10-year climatic data for 51 weather stations (46 stations for preparing ET0 maps and 5 stations as validation station) were gathered over Mazandaran province. Semivariograms were calculated and the best semivariogram model was selected on the basis of the least value of Residual Sums of Squares (RSS). The spatial correlation of the data was compared on the basis of Nugget to Sill ratio. The data were interpolated using Ordinary Kriging method and the interpolation error was computed by cross validation technique based on Root Mean Square Standardized Error (RMSSE). The predicted ET0 values were compared to the computed ET0 in validation stations and sensitivity analysis was conducted. Results show the second approach had better spatial correlation and lower interpolation error and the difference between these two approaches were not significant. Therefore, the accuracy of the ET0 maps is more related to the method of computing ET0 than the type of climatic data is being interpolated.

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Water productivity is a major challenge in all agricultural regions and despite the use of pressurized irrigation system, it has not increased as expected in Iran. In addition, in spite of water shortage in Iran, gardeners because of lack of knowledge in economic consequences do not welcome deficit irrigation and irrigation scheduling. To this end, optimization of irrigation water depth in an orange orchard was conducted for two irrigation scheduling methods (with and without 4 days irrigation frequency) under water and land limitations conditions by mathematical analysis of production and cost functions. Then, their effect on the net income by changing in water and fruit price was assessed. Production and cost functions were developed based on two scenarios of applied water including only irrigation water depth and irrigation water depth plus rainfall. According to results, when water is limiting, by using the optimum water depth (Ww), 26% of irrigation water use can be saved that causes only 3–4% decrease in the net income per unit of land and 16% increase in the net income per unit of irrigation water. In addition, when water limiting is serious, using 46% deficit irrigation (Wew) is more useful and resultes the highest water productivity, even though it causes 14–17% decrease in the net income per unit of land. However in water limiting condition, if land is not limiting, using Wew causes the maximum net income per unit of land even 50–60% more than full irrigation. Moreover, using the optimum water depths in water limitation conditions (Ww and Wew) increases the water productivity 26–47% relative to full irrigation. On the other side, the net income and the amount of optimum water depths are not sensitive to the price of water at the present value of water. However, they are highly sensitive to the price of fruit. Furthermore, having an irrigation schedule causes 27% increase in the net income per unit of land. According to positive effects of deficit irrigation and irrigation scheduling on the water productivity and the income, they are highly recommended for addressing water scarcity in Iran.

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