Assessment of Changes in Water Resources of the Upper Aras Transboundary Basin Under the Influence of Increasing Cultivated Area, Using the SWAT Model and Global Climate Databases

The Upper Aras transboundary Basin, shared between Turkey and Armenia, has undergone significant agricultural development in recent decades, primarily in Turkey under the DAP project. This development has reduced water outflow from the basin, negatively affecting downstream countries. Due to the limited access to ground-based data, this study investigated these changes in water resources using CFSR and CRU global climate data, Landsat satellite imagery, and the SWAT model, as well as extensive review of the available regional reports. Results indicated that over the past 15 years, the basin has experienced increased temperatures and a slight rise in average rainfall. Also, it was revealed that the area of irrigated croplands has increased from 140,000 hectares in 1983–2008 to 230,000 hectares in 2009–2018. These changes were applied to the calibrated SWAT model in three scenarios. Among them, the results of one of the development scenarios defined as the expansion of the current cropland area, showed a decrease in the annual runoff volume of Upper Aras River from 2605 to 2155 MCM/year, representing an 18% reduction in the annual flows. Notably, the largest drop in monthly flows happened in May which was 26%. Furthermore, average agricultural water consumption in Turkey's Erzurum and Kars provinces were estimated at 494 mm/ha and 458 mm/ha, respectively, highlighting the impact of agricultural expansion under the DAP project on water resources.