Estimation of water footprint components of Iran's wheat production: comparison of global and national scale estimates

The water footprint (WF) of national wheat production has been previously estimated for the whole world in global-scale studies. These studies used assumptions which must be assessed and evaluated by estimates from national or regional studies. Here, previous estimates of different components (green, blue, gray and white) of WF of national wheat production in Iran were compared to the national-scale estimates. A new component (white WF) was proposed to account for the irrigation losses. Different components of the wheat WF were estimated for 236 plains over fifteen major wheat producing provinces. Then, the average values of each province were estimated. Finally, the weighted average values of each WF component were estimated by using the shares of irrigated and rainfed productions as weighting factors. The average total WF for irrigated areas and between all selected provinces is about 3,188 m/ton with comparable shares of blue and green water, while the average total WF for rainfed areas is about 3,071 m/ton with the share of the green WF nine times that of the gray WF. The results show that the total national WF of wheat production for the period 2006-2012 is about 42,143 million cubic meters (MCM) per year (41 % green, 18 % blue, 16 % gray and 25 % white) with the share of the green WF about 2.3 times the blue WF. Comparison of the obtained estimates with the results of the previous studies at a global scale revealed that estimating the WFs of crops at a global scale, ignores the variations of climatic conditions, water resources availability and crop yields at the national and regional levels and some of the assumptions made in global-scale studies must be reassessed