Exploring Hydrological Response to Land Use/Land Cover Change Using the SWAT+ Model in the İznik Lake Watershed, Türkiye

Land use/land cover (LULC) changes significantly affect hydrological processes in watersheds. In this study, the Soil and Water Assessment Tool (SWAT+) model was employed to investigate the hydrological response to LULC changes in the İznik Lake Watershed, a region of significant environmental and social importance in the Marmara Region of Türkiye. This study provides a novel understanding of water balance dynamics of the İznik Lake Watershed through hydrological modeling. The SWAT+ model was calibrated and validated against observed monthly flow data from two gauging stations using three objective functions: Nash–Sutcliffe efficiency (NSE), Kling–Gupta efficiency (KGE), and the percent bias (PBIAS). The model was utilized to evaluate the impacts of LULC change on water balance components such as surface runoff, percolation, lateral flow, water yield, and evapotranspiration. The results revealed that the expansion of urban areas and reduction in forest land have led to an increase in surface runoff and a decrease in lateral flow and percolation, which in turn have impacted the overall water yield of the watershed. The findings of this study can inform land use planning and management decisions to mitigate the negative impacts of LULC changes on water resources in the İznik Lake Watershed and similar regions.