Analysis of Dez Dam's Operational Performance in Meeting Downstream Water Demands Under Future Climate Scenarios

Abstract

Climate change and its associated impacts pose a significant challenge for water-resource management, especially in basins where reservoir operations are critical for meeting domestic, agricultural, industrial, and environmental water demands. This study evaluated how climate change will affect the operational performance of Dez Dam, located in southwestern Iran, and its ability to meet downstream water demands in the future. To this end, daily climate projections (precipitation and minimum/maximum temperatures) from five General Circulation Models (GCMs) under two emission scenarios (RCP4.5 and RCP8.5) were downscaled using quantile mapping and combined with Bayesian Model Averaging (BMA). We then simulated inflow to the Dez Dam reservoir using the semi-distributed Soil and Water Assessment Tool (SWAT) model. Finally, these results were fed into the MODSIM water-allocation model to assess the reservoir's performance in meeting various downstream demands across a baseline period (1984–2018) and three future periods: 2041–2060, 2061–2080, and 2081–2100. The results indicated that the Dez Basin's future climate will be characterized by decreased precipitation and increased temperatures. By the end of the century, total annual precipitation is projected to drop by approximately 17–18% under both RCP4.5 and RCP8.5 scenarios, while maximum and minimum temperatures are expected to show substantial increases. Reduced precipitation during winter and early spring—the basin's primary runoff-generation period—will lead to a significant decline in reservoir inflow. SWAT model results reveal that during the far-future period (2081–2100), the mean annual streamflow of the Dez River will decline by 56.8% under RCP4.5, while a more substantial reduction of 64.2% is projected under RCP8.5 compared to the baseline period of 1984–2018. The MODSIM assessment of reservoir performance showed that declining basin inflows will limit Dez Dam's operational capacity. While higher-priority demands, such as domestic water supply and Ghadeer industrial demand, are expected to maintain relatively high supply reliability, agricultural, environmental, and other downstream demands will face substantial reductions in future water supply. Specifically, the supply percentage for agricultural demands in Dez and Band-e Qir is projected to fall below 30% by the end of the century. Overall, these findings suggest that climate change may reduce the reliability of Dez Dam's operations, highlighting the need to revise water-allocation policies, manage demand, improve water-use efficiency, and develop adaptation strategies for future climatic conditions.