Climate and forest changes are regarded as two major drivers affecting streamflow in forested watersheds. A growing interest in forest hydrology research is quantification of the relative contributions of climate variability (dQ_C) and forest disturbance (dQ_F) to streamflow. Such quantification has been well conducted in annual mean flows. However, little study has been done on peak flows. Using long-term data from Upper Penticton Creek Paired watersheds located in Southern British Columbia, this study determined the relative roles of dQ_C and dQ_F on peak flows. Results showed that intensive forest disturbance (cumulative equivalent clear-cut area or CECA > 40%) significantly increased the magnitude (3.27 � 2.83 mm, 19.25%) and advanced the timing (8.42 � 11.75 days) of peak flows as well as shortened the duration of high flows (1.89 � 3.31 days). Peak flows were highly related to temperature, snow depth, and snowmelt rate rather than precipitation. The separation of relative contributions indicated that the impacts of climate variability (65%) were more pronounced in major flood events than forest disturbance (35%). These results verified the effects of both climate variability and forest disturbance on peak-flow changes. The implications of the methods and results from this study were discussed.