In this paper, the long-term hydrological response of a semi-arid trans-boundary basin to climate changes was analyzed. The basin is the Yarmouk River. The basin is located in a semi-arid region between Jordan and Syria. The methodology adopted is based on simulating the hydrological response of the basin under sstatistically downscaled climate change scenarios. For this goal, the physically process-based semi-distributed hydrological model Soil and Water Assessment Tool (SWAT) has been used. The impacts of climate change on YRB flow regime and water cycle components under pre-development and post-development conditions were evaluated by driving SWAT model under the projected 21st-century climate change scenarios. The scenarios applied were the SRES A1B and A2 and CMIP5 RCP 2.6, RCP 4.5 and RCP 8.5 that had been downscaled from the CGCM3 and CanESM2 climate variables output, respectively. These scenarios were downscaled by Statistical Downscaling Model (SDSM).The results showed that the YRB surface water is very vulnerable to climate change. Under the pre-development conditions, the impacts are believed to be at high risk. Under the post-development conditions, the impacts were of much less risk and proved the water harvesting is an efficient way for adaptation. The applied changes of temperature from +0.9 to +3.7 C˚ and of precipitation from +6% to -32% during the 21st century indicated a reduction in river flow ranges from -2.6% to 60% under the pre-development conditions and from -0% to -36.4% under post-development conditions. Such evaluation can help in enhancing the basin management, sustainable planning and building the adaptation schemes