The importance of climate data in hydrological process simulation is widely recognized. The evaluation of the hydrological budget response to climate variability is required especially in water resource management. The present paper illustrates a case study of sensitivity analysis for the hydrological model SWAT (Soil and Water Assessment Tool) using climate data from the Havrias river basin in north Greece. The ERA-Interim reanalysis daily climate data, were used as input data to drive the SWAT model. The SWAT model was calibrated for the period from 1981 to 2000. The sensitivity of the hydrological parameters to the alteration of the climate data was analyzed by using eleven hypothetical scenarios. These scenarios regard different combinations of temperature, wind speed, precipitation and relative humidity. The results show that the changes of precipitation temperature and relative humidity have significant influence in evapotranspiration and percolation (and consequently recharge) in the study region. On the contrary, the wind speed negligibly affects on the hydrological components. Overall, the Havrias river basin hydrological budget is sensitive to shifts in climate data and the utilization of reliable and accurate climate models outputs is necessary in order water managers to be able to build scenarios providing sustainability against the potential future climate change impacts.