|The Southeastern Anatolia Project (SAP) of Turkey is a multidimensional regional development project based on utilizing the waters of Euphrates and Tigris rivers by irrigating vast semi-arid lands and by producing hydroelectric power. The irrigation schemes carried out within the scope of SAP has already caused immense land cover / land use (LCLU) changes in the region. In this study, regional climate model simulations were performed to investigate the effects of irrigation-based LCLU changes on the regional climatology and water budget. For this purpose, two different land use maps in addition to default land use map of the regional climate model that reflect the pre-SAP landscape were used to simulate the current realization level of SAP (25%) and future (upon completion of SAP) LCLU. Reanalysis data (NNRP) for the 20 years between 1991 and 2010 and outputs of a global circulation model (EC-EARTH) for the period between 1986 and 2009 have been used to force the regional climate model (RegCM4) at a horizontal resolution of 48 km over Eastern Mediterranean and Black Sea region, and later on nested domain with 12 km resolution. High resolution gridded CRU (Climatic Research Unit) dataset was used to validate the results of larger domain. The regional model tends to overestimate precipitation in the headwaters region while giving fairly good estimates for the downstream areas. Dynamically downscaled results from reanalysis indicate that the annual surface temperatures will decrease by about 0.4-0.8 C due to the LCLU changes in the region, while precipitation will increase 3-7%, mostly in spring. Increase in evapotranspiration amounts to 51-114% over the pre-SAP conditions, which means significant water loss from the region. Additionally, the study is currently being extended to simulate the integrated effects of future climate changes (RCP 4.5 and RCP 8.5 scenarios by using EC-EARTH) with anthropogenic climate changes (land cover land use changes) for the assessment of possible changes in the regional water budget.