Periyar reservoir is the major reservoir located in upstream of the main stream of river Vaippar having adequate flow during northeast monsoon. In this paper, the impact of climate change on inflow into that reservoir has been analysed using SWAT (Soil and Water Assessment Tool) model. In the model, a combination of change of precipitation (10%, 20%, -10%, and -20%), temperature (increase of 2 degrees C, 4 degrees C, and 6 degrees C) and regional climate change scenario (A2 and B2) is given as input and the changes in river discharge and reservoir inflow are studied. It is found that the reservoir inflow are very much sensitive to decrease in precipitation (-29.1%, -28.9% for a decrease of -10%, -20%) compared to increase in precipitation (21.4%, 22.4% for an increase of 10%, 20%). Also, it is determined in this study that the changes in precipitation, rather than temperature, would have a significant effect on reservoir inflow since precipitation is the main driving force to stream flows.