Assessment of the effect of climate change in anticipated water resources availability in arid climate zones

Climate change impact and drought phenomena linked with anthropogenic pressure have become a growing concern for water resource managers and policy makers, particularly in arid and semi-arid regions. This research proposes generic methodologies to evaluate 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. These methodologies have been achieved through the following: (1) Highlight the impact of potential evapotranspiration (PET) methods, elevation, and climatic conditions on the reconnaissance drought index (RDI) results, applying three of the most widespread PET estimates, which are Thornthwaite, Hargreaves, and Blaney-Criddle in addition to the Food and Agriculture Organization Penman-Monteith reference technique, using data from 24 stations cover different elevations and climatic conditions for the period from 1979 to 2014. The initial form of RDI is directly influenced by the selected PET method at different elevations for all regions. (2) Combine the results of the flow duration curve and the digital filtering algorithms to overcome the limitations of the traditional baseflow separation methods, and then determine the baseflow annual variations. The water yielded from the basin storage system during the dry seasons resulted in dissimilarities in the observed baseflow index between the pre-damming and post-damming periods of the streamflow. (3) Quantify the hydrological alterations of various flow characteristics utilise the Indicators of Hydrologic Alteration method, in addition to multi-regression, hydrologic sensitivity, and hydrologic model simulations. Climate change was the main factor reducing streamflow. (4) Compare the results of seven ensembles General Circulation Models (GCM) with the results of delta perturbation (DP) scenarios. Both scenarios predicted almost identical decreases in the mean monthly flows to the reservoir. The DP scenarios allow the sensitivity of the impact models to climate change to be more evidently determined compared to GCM scenarios so that they could be complemented GCM scenarios