For analyzing the effect of climate change on the streamflow at a regional scale, six General Circulation Models (GCMs) were selected from among eighteen GCMs from the Coupled Model Intercomparison Project (CMIP5) for the Pajaro River Watershed in central California. The 1/8° latitude-longitude resolution bias-corrected and downscaled CMIP5 projections were utilized for an ensemble of GCMs under four Representative Concentration Pathways (RCP2.6, RCP4.5, RCP6.0 and RCP8.5). The twenty-first century is segregated into three time-periods (2016-2039, 2040-2069 and 2070-2099) for comparing the streamflow against changing precipitation and temperature according to the CMIP5 projections. The daily maximum and daily minimum temperature are projected to consistently rise through to the latter part of the century. Csiro-mk3-6 and canesm2 models project an increase of 3.1°C in annual average daily maximum temperature and 3.4°C in annual average daily minimum temperature respectively in 2070-2099 period under RCP8.5 scenarios. Future precipitation is projected to increase in January and February, which means the wet months in the Pajaro River Watershed are likely to get more rainfall. The dry months would continue to receive diminished precipitation throughout the century. The streamflow was increasing on future January, and sporadically, in February months but diminished during the dry months. The range of annual average streamflow for the future years stretched from 0.1 to 29.1 m3/s for the GCM ensemble, mostly close to the lower limit. The results suggest considering multiple climate change scenarios and evaluating alternative setups would provide a robust basis for hydrological assessment.