Modeling of the upper tigris sub-basin's run-off and hydrologic model with the swat method

The sustainable management of water resources has become increasingly important, particularly in semi-arid regions where the effects of climate change are being strongly felt. Rising global water demand, changes in land use patterns, and the disruption of the hydrological balance highlight the necessity for scientifically based water resource planning at the watershed scale. In this context, hydrological models, especially those based on physical principles, provide significant opportunities for the detailed analysis of rainfallrunoff relationships and the components of the water cycle. In this study, the spatial and temporal distributions of basic hydrological components (surface runoff, infiltration, evapotranspiration, and groundwater flow) were analyzed along with rainfall-runoff processes using the SWAT model in the Upper Tigris Sub-Basins, which are located in the Southeastern Anatolia Region and possess a strategic hydrological structure. The Upper Tigris Sub-Basin is situated in southeastern Turkey, constituting the upper reaches of the Tigris River and covering specific parts of the provinces of Diyarbakır, Elazığ, Batman, Bingöl and Mardin. Characterized by a mountainous and rugged topography, the basin exhibits highly variable flow dynamics due to its elevation range, which varies between 495 and 2937 meters. In the region, where a continental climate prevails, the flow regime largely depends on snowmelt and spring precipitation. These characteristics make the region noteworthy in terms of both flood risk and drought period management. During the model setup process, topographic, geographic, and meteorological observation data were integrated to perform the watershed simulation. According to the model results, the observed peak flow was recorded as 82.10 m³/s, while the simulated peak flow was calculated as 85.28 m³/s. The calibration and validation stages of the model were conducted using the SUFI-2 algorithm through the SWAT-CUP software, and model performance was evaluated using statistical indicators such as NSE, R², and PBIAS. The results showed that the NSE value was 0.506, the R² value was 0.521, and the PBIAS value was -8.218%. These findings indicate that the model produced reliable simulation outputs. This thesis scientifically investigates the hydrological structure of the Upper Tigris Basin and demonstrates the applicability of the SWAT model in similar basins. In addition, it provides valuable insights to support decision-makers in water resources management and the evaluation of climate change scenarios.