Development of a System Dynamics Model for Prediction of Karaj Reservoir Share in Tehran Water Supply

Tehran’s water consumption (TWC) is rising as a result of rapid population growth, climate change, and precipitation decline. As water resources of Tehran are also affected by a variety of factors, the water supply scheme becomes so complicated and it is necessary to consider the complexity and dynamics interactions in water supply system before any decision making. In this study, Karaj reservoir as an important surface water resource of Tehran’s water supply system was modeled through system dynamics (SD) approach for prediction of Karaj Dam share in Tehran water supply. The SD model was implemented in AnyLogic software using the historical data from April 2006 to March 2022, and the stock and flows and dynamics variables were predicted for April 2023 to March 2023. The novelty of this research is the development of SD model of Karaj Dam to simulate its relationships and interactions for prediction of Karaj Dam share in Tehran water supply in 2023. In this regard, the TWC and Karaj Dam inflow were predicted by using SARIMA(1,0,0)(0,1,1)12 model for April 2023 to March 2023. Finally, to assess the precision of the results obtained from the SARIMA and SD models, the criteria of coefficient of determination (R2), Error percentage (E%), and Nash–Sutcliffe model efficiency coefficient (NS%) was calculated. The results showed that the Karaj Dam inflow will be decreased during April 2023 to March 2023 due to the precipitation decline, consequently the Karaj Dam reservoir volume will be reduced and for this reason less water can be harvested from Karaj Dam reservoir for different applications. Therefore, it is clear that in the future we will have faced the challenge of water supply in Tehran.