Investigating the impacts of climate change on water resources in Bartin province using the swat model

In this thesis, the sensitivity of the flow regime and water balance to climatic conditions in the Bartın Arıt sub-basin within the boundaries of Bartın province was investigated using the process-based SWAT2012 watershed model. The digital elevation model (DEM), land use and land cover, and soil datasets were prepared at a common resolution in the EPSG:32636 (UTM 36N) coordinate system. The basin boundary, stream network, sub-basins, and hydrologic response units (HRU) were derived using QSWAT. Meteorological inputs were generated from daily precipitation (PCP) and maximum–minimum temperature (TMP) series, and potential evapotranspiration was calculated using the Penman–Monteith approach. The model was run at a daily time step for the 2010–2023 period. The 2010–2011 period was separated as the warm-up period, and evaluations were performed at a monthly scale. Monthly FLOW_OUT discharges simulated for Darıören Akım Gözlem İstasyonu (AGİ) at the outlet were compared with DSİ observations. Parameter calibration and validation were conducted in SWAT-CUP using the SUFI-2 algorithm. To address the minor difference between the model area (≈130 km²) and the station drainage area (137 km²), observed discharges were scaled by the area ratio of 130/137 (=0.95). Model performance was evaluated using NSE, KGE, R², RSR, and PBIAS. In the calibration period (2012–2018), NSE=0.79, R²=0.84, KGE=0.71, RSR=0,46, and PBIAS=−16.9% were obtained. In the validation period (2019–2023), NSE=0,78, R²=0,83, KGE=0,70, RSR=0,47, and PBIAS=−20.9% were obtained. Negative PBIAS values indicate that the model tends to simulate higher mean discharge compared with observations. In addition, annual water balance consistency was checked by compiling precipitation, actual evapotranspiration, and flow components from the TxtInOut outputs. Overall, the calibrated SWAT model provides a reproducible basis for the quantitative representation of the flow regime and water balance components in the Bartın Arıt sub-basin.