Introduction and Goal Water, energy, and food form the basis of the sustainable development of societies and are inextricably intertwined. Thus, a change in any of them can have direct and indirect consequences on the others. The objective of this study is to provide and develop a new methodological approach that can efficiently support the decision-making and policy-making process regarding the supply and demand of a watershed’s resources, and to quantitatively model the sustainability of water, energy, and food based on the system dynamics approach across different scenarios. The structure of this framework can be used as an effective tool to improve policy-making and elevate the level of watershed sustainability, providing more efficient perspectives in resource management. Materials and Methods In this study, a quantitative and integrated framework based on system dynamics (SD) was developed and modeled, emphasizing resource supply and demand interactions through a Water-Energy-Food nexus approach in the Sarab Sayed Ali watershed. Since accurate and reliable SD modeling for assessing resource sustainability requires a comprehensive and transparent database, the necessary data were collected from official and credible national authorities. For modeling and validation in the study area, historical data recorded between 2001 and 2023 were utilized as inputs for the Vensim software. Furthermore, the simulation time step was set annually, and the overall modeling horizon was established from 2001 to 2046 considering technical aspects and the long-term policy orientations of the Iran Water Resources Management Company to enable the prediction of the system’s future behavior. Following model development, validation was performed using standard SD tests, such as the boundary adequacy test, dimensional consistency test, and behavior reproduction test, and the results were analyzed based on feedback loops. By integrating the findings from the sensitivity analysis with the local characteristics of the region, various scenarios were defined and applied to the model. Ultimately, the most optimal scenario was ranked and selected using the Fuzzy TOPSIS Multi-Criteria Decision-Making method. Results and Discussion Considering the variables related to the water, energy, food, and social and economic sectors, the modeling process was carried out from 2001 to 2046. After model validation, the results showed that the population residing in the watershed, which was 56400 people in the year 1380, will reach 85770 people by the year 1425 based on the conducted modeling using variables such as birth rate, mortality rate, and migration rate. This indicates an approximate growth of 52%. From 2001 to 2046, the region's water resources have faced a significant decrease, with the volume of surface water declining by about 21 million cubic metres in the first period from 2001 to 2005 and by 2 million cubic metres in the second period from 2006 to 2046. During the modeling period, the volume of groundwater decreased by about 1.77 billion cubic metres, while the total decrease in water resources (surface and underground) is estimated at 1.79 billion cubic metres. The level of energy sustainability (fossil and electrical) showed an upward trend from 1380 to 1400, reaching 2.2 million barrels of oil equivalent. Between 2022 and 2040, the energy level entered a downward phase but remained positive and was sufficient to meet the region's needs. From 2041 to 2046, the energy sustainability index dropped to negative values, reaching minus 1.8 million barrels of oil equivalent by 2046. This indicates a sharp decline in energy sustainability and the emergence of significant challenges in this sector. Regarding food resource sustainability, considering all four sources (agriculture, livestock and poultry, fisheries, and livestock and poultry feed of agricultural origin), the trend was upward from 2001 to 2030, with the food supply exceeding demand by about 597 thousand tonnes by 2030 From 2031 to 2046, this trend changed, and food reserves decreased to 390 thousand tonnes in 2046, indicating a reduction in reserves and a weakening of the sustainability of food resources. After the modeling process, the results of the sensitivity analysis showed that, in the water subsystem, the groundwater share of consumption and irrigation efficiency; in the energy sector, the fossil energy share and per capita energy consumption in the residential and commercial sector; and in the agricultural sector, the beet cultivation area and per capita food consumption are considered key variables. Based on the findings from the sensitivity analysis and the identification of effective leverage points in the model, the consumption pattern modification scenario with a proximity coefficient of 0.755 is introduced as the best option to improve resource sustainability. In contrast, the base case scenario, with a proximity coefficient of 0.189, is the least effective in improving resource sustainability. Conclusion and Suggestions Comprehensive management and planning in watersheds have a complex and multidimensional nature, as hydrological, social, economic, and environmental dimensions are intricately interconnected and influence one another. Achieving effective management in such a system requires a scientific, accurate, and in‑depth understanding of the challenges and interactions among various components such as water, energy, and food resources. Despite the effectiveness of the nexus approach with a systems perspective, its implementation still faces challenges such as the lack of accurate data, the interdisciplinary nature of the subject, the complexity of economic and social structures, and existing gaps in policymaking. Nevertheless, developing more comprehensive nexus models that consider uncertainties and climate change can facilitate informed decision‑making and sustainable resource management through improving consumption patterns, diversifying resources, utilizing modern technologies, and strengthening risk management. |