Document Type : Research Paper
Materials and Methods
Calculate the cost of water
The study employed the engineering economy approach to calculate the cost of each cubic meter of water. This approach considers all capital costs, operation and maintenance expenses of facilities, and other relevant costs throughout the entire lifespan of the project. By creating a cash flow table of costs, the total cost of water is calculated using this method of engineering economics (Tahamipour Zarandi and Yazdani, 2016).
Yield function
To estimate the quantity of product produced based on the volume of water consumed, the water-production relationship presented by Rao et al. (Rao et al., 1988) was employed. According to equation (1), the yield function of crops during various growth periods has a linear correlation with the volume of water consumed.
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where Ya is the actual yield in tons per hectare, Ym is the potential yield in tons per hectare, Kyi is the coefficient of sensitivity of the crop to water deficit during the i-th growth period, AETi is the amount of water given to the plant (evaporation or actual transpiration) during the i-th growth period in cubic meters, PETi is the water requirement of the plant (potential evapotranspiration) during the i-th growth period in cubic meters, and n is the number of growth periods for each plant.
Productivity
There are different types and numbers of productivity indicators depending on different perspectives. In this study, the financial index of water efficiency was used, which is in line with the main objective. This index is the ratio of net income per unit of water volume, also known as Net Benefit Per Drop.
Results and Discussion
The estimated price of each cubic meter of water using economic and engineering relations was 8,595 rials. In the current situation (water supply at the price of 940 Rials), the Qazvin Plain irrigation network's income is approximately 89 billion Tomans. However, if each cubic meter of water is supplied at the price of 8,595 Rials, the current model of water cultivation and distribution not only fails to generate income for farmers but also causes them harm. Through the optimization of the cultivation pattern, the income of the Qazvin Plain irrigation network can increase to about 101 billion Tomans. Simultaneously optimizing the cultivation pattern and water distribution can lead to an income of approximately 233 billion Tomans. The Net Benefit Per Drop (NPBD) increases by an average of 40% by optimizing the cultivation pattern and by an average of 389.6% by simultaneously optimizing the cultivation and water distribution pattern compared to the current situation where each cubic meter of water is supplied at 940 Rials. However, in the case of supplying each cubic meter of water at the price of 8,595 Rials and not changing the cultivation and water distribution pattern, the average NPBD will decrease by 289.4% compared to the current situation. By optimizing the cultivation pattern, it is found that with the increase in water price and decrease in gross profit, the model tends to cultivate crops that have higher yield and less sensitivity to water stress. According to this, sugar beet and potato are the most suitable crops for cultivation in the Qazvin Plain irrigation network. Although other crops, such as wheat and barley, have low sensitivity to water stress, their low yield and subsequent decline in the irrigation network's income make them less desirable for cultivation.
Result
The price of water is one of the important economic variables that can play a significant role in the optimal use of water resources in the agricultural sector. By implementing water pricing policies, the final cost of production increases, and it becomes essential to select a crop combination that yields higher benefits per unit of water. This study focuses on estimating the total cost of each cubic meter of water using engineering-economic relationships and its impact on the economy of farmers under two optimization models: optimizing the cropping pattern and simultaneously optimizing the cropping pattern and water distribution. The total cost of each cubic meter of water was estimated at 8,595 rials, and the results showed that the current cropping pattern is not suitable if the price of water increases. However, by optimizing the cropping pattern and simultaneously optimizing the cropping pattern and water distribution, it is possible to achieve an income approximately 14.7% and 162.7% higher than the current situation where the price of each cubic meter of water is 940 rials, respectively.
Acknowledgments
The Qazvin Regional Water Company expresses its utmost gratitude and appreciation to the Agricultural Jihad Organization, which has cooperated in carrying out this research.