Water–Food Nexus Modeling for Assessing Watershed Sustainability Using a System Dynamics Approach (Case Study: Sarab Seyed Ali, Lorestan Province)

Food production is closely linked to water availability. In this context, water–food nexus modelling was conducted using system dynamics, based on water, food, and population data, with an emphasis on sustainability through analysis of supply and demand differences during the period 2001–2046, using VENSIM software in the Sarab Seyed Ali watershed. After structural and behavioral validation, the results showed that water resources over the 45-year period would decline by 1.57 billion cubic meters, most of which is due to groundwater depletion. For food resources, from 2001 to 2031, food sustainability improved, so that by 2031 food supply exceeded demand by 715 thousand tons. However, between 2031 and 2046, this trend reversed, and food accumulation in 2046 reached 485 thousand tons, reflecting a reduction in food reserves compared to 2031. Sensitivity analysis, considering regional conditions, identified the cultivated area of beet as the most influential factor in the model. Moreover, four scenarios: baseline, crop pattern change, wastewater system development, and livestock and poultry management were applied to the model and evaluated. Comparing the results of the three scenarios with the baseline (Scenario 1) showed that Scenario 3, with a reduction of 1.03 billion cubic meters in water resources, and Scenario 4, with an increase of 2.08 million tons in food supply, could enhance sustainability compared to the other scenarios. Therefore, adopting systemic and practical strategies within the framework of management policies can significantly improve sustainability.
 
Extended Abstract
1-Introduction
Food production is closely linked to water availability. Because the water and food sectors are highly interconnected, they cannot be managed separately; water supply limitations and poor water resource management negatively affect food production and undermine the sustainability of food resources. It is therefore essential to identify various tools that support comprehensive analysis of water and food security by establishing temporal and spatial linkages between these sectors. One such tool is the correlation approach, which enables a holistic understanding of resource interdependence and highlights the need to address sustainable and innovative challenges in water management to achieve food security. System dynamics can be used to conceptualize and model the complex relationships between water and food components. Applying a system dynamics approach, with a focus on physical and environmental components within scenario frameworks, can provide an innovative basis for resource policymaking and help enhance sustainability at the watershed level.
 
2-Materials and Methods
In this study, a water–food nexus model was developed using a system dynamics approach for the period 2001 to 2046, based on water and food resources and consumption in the Sarab Seyed Ali watershed, located in the northern part of Lorestan Province. The water and food resources and uses in this watershed are modeled as a dynamic, integrated two-component system, with emphasis on physical and environmental aspects, within the system dynamics environment of VENSIM software. The model is validated using methods such as boundary adequacy, dimensional consistency, and reproduction tests. After modeling, and based on the results of sensitivity analysis, regional characteristics, and the identification of factors affecting water and food sustainability, four basic scenarios – changing the cultivation pattern, developing the sewage system, and managing the number of livestock and poultry – were applied to the model to enable decision-making and planning for future supply and demand management.
 
3- Results and Discussion
The structural validity of the model was confirmed through two tests: the adequacy of model boundaries and the dimensional consistency of the model. Behavioral validity was also verified, with the RMSPE index below 0.1 for key variables such as population accumulation and water demand in the drinking and urban sectors. Model validation results indicated that the population would increase from 56,400 in 2001 to 85,770 in 2046, representing a steady growth of approximately 52% over 45 years. Water resources are projected to decline by 1.57 billion cubic meters during this period, primarily due to a 1.56 billion cubic meter reduction in groundwater reserves. In the food resources sector, sustainability improved between 2001 and 2031, with food supply exceeding demand by 715 thousand tons in 2031. However, this trend reversed between 2031 and 2046, and food accumulation dropped to 485 thousand tons by 2046, indicating a decline in food reserves. Sensitivity analysis showed that a ±10 percent change in the area under sugar beet cultivation had the greatest impact on the model, while water consumption for producing one unit of fishery product had the least effect. Based on the results of the sensitivity analysis and regional characteristics, four core scenarios were implemented within the modeling framework: modification of the cropping pattern, expansion of urban and industrial wastewater systems, and regulation of livestock and poultry numbers. By implementing the three proposed scenarios (scenarios 2, 3, and 4) and comparing their outcomes with the baseline model (scenario 1), it can be concluded that all three scenarios play an effective role in improving water resource management. However, scenarios 2 and 4, in particular, have a direct and significant impact on the sustainability of food resources and regional food security.
 
4- Conclusion
In comprehensive planning and decision-making for watershed management, numerous complex and interconnected challenges arise that require precise, in-depth, and scientific understanding of the issues and obstacles in these areas. Without such insight, current problems will remain unresolved, and mismanagement of resources and facilities may lead to new and fundamental crises across social, economic, and environmental dimensions. Also, by purposefully combining different scenarios, an efficient management framework for water and food can be designed to increase the resilience and sustainability of the system through synergy between key components. Therefore, adopting systemic and practical approaches within the framework of sustainability policies – such as reforming consumption patterns, diversifying resources, managing and recycling resources, employing modern technologies, and implementing risk management – is both essential and inevitable.