Systemic Management of Water Resources with Environmental and Climate Change Considerations

River basin management is very varied and challenging due to the competition in water consumption in different parts. Therefore, modeling water resources and uses is complicated, time-consuming, and essential in catchments with a complex hydro system. In the present study, modeling was performed for the southeastern part of the Aras River catchment area located in Iran. In this area, there is intense competition for water due to the implementation of policies to increase the cultivation area and the need to provide environmental water rights, which causes a lack of water supply for some sectors. In this study, water supply and demand in five sub-basins of Aras River were investigated using the WEAP MABIA model. Four separate scenarios, including a reference scenario (S1), the reference scenario with a priority of meeting environmental demands (S2), and climate scenarios (S3, S4) under general circulation models (GCMs) based on the IPCC Sixth Assessment Report (AR6) were produced for the near (2021–2040), middle (2041–2060), and far (2061–2080) future periods. Scenarios S3 and S4 considered the policy of increasing efficiency and the cultivated area to evaluate the response of sub-basins to changes in demand. The simulation results of scenario S1 show that the current water resources provide the existing requirements in wet years but are insufficient in dry years and years of increasing the cultivated area. Water shortage will also rise due to the policy of increasing the cultivated area and the impact of climate change, especially in scenarios S3 and S4. The results also indicated that the rate of lack of environmental water rights and the deficit of three aquifers in the study area will increase significantly in scenarios S3 and S4 in comparison with scenarios S1 and S2, which requires the adoption of appropriate management policies to achieve sustainable water resources for all subsections.