Impact of Subsidy Policy on the Drip Irrigation Systems under Non-Volumetric and Volumetric Water Allocation in the Najafabad Aquifer

This study determines the amount of irrigation water saved as a result of the subsidy policy to adapt from flood to drip irrigation. We developed a positive mathematical programming model (PMP) to evaluate the effect of economic incentives on farmers’ decisions to choose the type of irrigation technology, cropping pattern, and "water use" and "water consumption" in rural Garkan Shomali district, which is part of the Najafabad aquifer. We collected data through farm surveys, desk research, and expert interviews. The results showed that a reduction in the financial costs of converting flood irrigation into drip irrigation can lead to farmers investing in this technology. In the current water allocation scenario, the subsidy policy increases the water consumption of drip-irrigated crops by 28%, of which 19% is non-consumed water before subsidy payment and the rest is related to the reduction of furrow-irrigated lands. Also, under non-volumetric water delivery conditions, the operating costs reduce and the net income of the farms increases because of the increase in efficiency and the development of the area under cultivation, which increases water consumption while the water use is constant. In the volumetric water delivery scenario, with the increase in subsidies, the net income of the farms will increase without developing the area under cultivation and only because of the increased yield. Therefore, subsidy policy increases irrigation efficiency at both the farm and regional levels and is an effective tool for dealing with drought conditions.