Streamflow Alteration Impacts with Particular Reference to the Lower Zab River, Tributary of the Tigris River

Abstract

Climate change and drought episode impact integrated with anthropogenic pressure have become an increasing concern for water resource managers, particularly in arid and semi-arid climatic zones. This chapter presents a comprehensive methodology to predict the prospective impact of such changes at a basin scale. The Lower Zab River Basin, northern Iraq, has been selected as a representative case study. The methodology has been achieved through estimation of drought severity and climate change impact during the human intervention periods to separate the influence of climatic abnormality and measure the hydrologic deviations as a result of streamflow regulation configurations. The Indicators of Hydrologic Alteration (IHA) method has been applied to quantify the hydrological alterations of numerous hydrological characteristics. The Hydrologiska Byråns Vattenbalansavdelning (The Water Balance Department of the Hydrological Bureau) hydrologic model was used to define the boundary conditions for the reservoir capacity yield model, which was applied to derive the reservoir capacity-yield-reliability relationships, comprising daily reservoir inflow from the basin with the size of 14,924 km² into a reservoir with the capacity of 6.80 Gm³. Owing to the future precipitation reduction and potential evapotranspiration increase during the worst case scenario (−40% precipitation and +30% potential evapotranspiration), substantial reductions in the streamflow of between −56% and −58% are anticipated for the dry and wet seasons, respectively. Model simulations recommend that the reservoir reliability would generally decrease due to a decline in reservoir inflow. The study outcomes assist water resource managers and policymakers responsible for mitigating the effects of climate change.