Proposing the Structure of a Multi-Objective Mathematical Programming Model with Water-Food-Energy Nexus Approach for Crop Production

IntroductionWith the growing population of the world, water, food and energy supply will be one of the most important challenges ahead. Agriculture as the most important food producer is not only the consumer of water and energy, but also the most important supplier of energy. As a result, a balance must be struck between harvesting and exploitation of production resources and the amount of agricultural production. Due to the close relationship between water-food-energy systems and also their interaction with each other, a new concept called the “nexus” approach has been proposed which refers to the integrated nature and interactions of water-food-energy planning. This approach has provided suitable options for political decision makers, managers and planners in order to conserve existing resources and achieve sustainable development.Material and MethodsIn this study, we have tried to introduce a mathematical programming model using multi-objective mathematical programming (MOP) technique for water-food-energy nexus that has the ability to process managerial decisions. In this model, in addition to examining the economic aspect, the control of greenhouse gas emissions has also been investigated. The regions of Mashhad, Chenaran and Torqabeh-Shandiz are the most important regions in the study area of Mashhad province in the production of crops. The data required for the study were collected through review of reports and agricultural statistical yearbooks of the year 2020-2021 and interviews with experts in each region and through consulting engineering companies. The hypothetical model under study includes lands covered by crops of Mashhad, Chenaran and Torqabeh-Shandiz. In this model, the water needed to irrigate crops is supplied from surface and groundwater sources. Electricity (electricity consumption) is used to collect and pump of irrigation water, produce food, and supply the domestic and industrial sectors. In the process of generating electricity, production of food, irrigation of crops and consumption of fertilizers and pesticides, greenhouse gases are emitted, especially CO2. In this study, 6 objectives including: maximizing gross profit, maximizing the production of calories from food, minimizing emission of greenhouse gases, minimizing consumption of fertilizers and pesticides, minimizing consumption of irrigation water, and minimizing consumption of energy have been pursued.  Results and DiscussionThe results of the proposed model showed that the rate of change in the level of cultivation area in MOP compared to the current cultivation pattern in Mashhad, Chenaran and Torqabeh-Shandiz decreased by 25.92%, 53.05% and 55.88%, respectively. The level of optimal cultivation for barley in Mashhad in order to maximize net profit objective increased by 16934 hectares (46.71%) and its maximizing caloric production equal to 8484 ha, which has decreased compared to the current pattern (22%). The cultivation area of barley in minimum irrigation water consumption decreased by 10877 hectares (1.11%) and in other minimization objectives it changed to 12892 hectares which increased by 17% in Mashhad region. Wheat, barley, alfalfa, corn, sugar beet, tomato and potato have the highest decrease in cultivation area in the MOP among crops. The total area of optimal cultivation in the net profit maximization model of Mashhad, Chenaran and Torqabeh-Shandiz equal to 48639, 26027 and 75 hectares, which showed an increase of 41.4%, 11.61% and 55.8%, respectively. Furthermore, in the model aimed at minimizing energy, irrigation water, fertilizer, pesticide consumption, and greenhouse gas emissions, the recommended cultivation areas are as follows: 25,475 hectares for energy consumption, 15,954 hectares for irrigation water consumption, and 100 hectares each for fertilizer consumption, pesticide consumption, and greenhouse gas emissions. These figures clearly indicate the need to reduce the cultivation area dedicated to agricultural products that have a significant environmental impact. Consequently, it is crucial to alter the cultivation pattern and adopt a strategy that focuses on producing crops with a lower environmental impact. By implementing this strategy, the objective is to cultivate crops that require less energy, irrigation water, fertilizer, and pesticides, while also minimizing greenhouse gas emissions. This approach aims to mitigate the environmental footprint associated with agricultural practices. By reducing the cultivation area for crops that have high environmental effects and transitioning towards crops that have a lesser impact on the environment, it is possible to achieve a more sustainable and environmentally friendly agricultural system.ConclusionThe purpose of this study was to propose a nonlinear multi-objective mathematical programming model with water-food-energy nexus approach for crops in Mashhad province. In this study, in addition to economic relations, energy and environmental issues (greenhouse gas emissions) were also analyzed. The various components of the water-food-energy nexus, including energy supply planning, water supply and demand, food production, and control of greenhouse gas emissions, were modeled. The results showed that considering the MOP model based on economic and environmental objectives, the area under cultivation of wheat, barley, alfalfa, tomatoes, sugar beets and potatoes has significantly decreased. In other words, in order to achieve the objectives of maximum profit and minimum environmental impact, the area under wheat, barley, tomato, corn should be reduced and the area under cucumber, onion, potato and sugar beet should be increased. According to the results of this study, the following suggestions are presented:- Implementation of the proposed optimal model of water-food-energy nexus allows farmers to simultaneously maintain economic income, environmental considerations, optimal and sustainable consumption of resources (water-food-energy) to select and consider suitable policies. So, it will only be a sustainable policy if it can be built within the combined framework of water, food, energy and the environment.- In order to minimize the emission of greenhouse gases and its damage to the environment, the area under cultivation of agricultural products that have high environmental impact should be reduced, and in contrast to changes in cultivation pattern, the strategy to produce crops with less impact. Therefore, by developing a cropping pattern model, the productivity of the production capacities of the agricultural sector can be maximized and at the same time the damages and destructive consequences of crop production can be reduced.