Bushfires are common in Australia and can cause vegetation loss and affect hydrological processes such as interception, evapotranspiration, soil water storage and streamflow. This study investigates bushfire impacts on catchment mean annual streamflow for 14 Australian catchments that have been severely impacted by the 2009 Victoria bushfire, the second worst bushfire disaster in Australia. A statistical approach based on sensitivity coefficients was used for quantifying the climate variability impacts on streamflow and the time-trend analysis method was used to estimate the annual streamflow changes due to bushfire respectively. Our results show that bushfire has caused a noticeable increase in mean annual streamflow in majority of burnt catchments for an immediate post bushfire period (2009-2015), when the bushfire impact on streamflow is evidently larger than the climate change impact. Furthermore, the bushfire impact on mean annual streamflow linearly increases with the burnt percentage area. These results provide strong evidence for evaluating large-scale bushfire impact on streamflow at small to medium sized catchments, and guidance for process-based hydrological models for simulating bushfire impacts on hydrological processes for the immediate period after bushfire.