Forest insect outbreaks can cause significant tree defoliation and mortality, resulting in reduction of forests canopies that increases catchment runoff and decreases the proportion of baseflow. However, our understanding of the long-term impact of insect defoliation on catchment hydrology is limited. This study is a continuation of a previous catchment hydrology study (2019-2021) that looked at the effects of cumulative defoliation by spruce budworm (Choristoneura fumiferana) on stream discharge and runoff in 12 experimental catchments (6.33–9.85 km2) across the central Gaspé Peninsula in eastern Quebéc, Canada that spanned a range of defoliation intensities. Specifically, we extend (2022-2024) the original study to assess the hydrological impact as the outbreak continued to intensify, ultimately resulting in tree mortality. Runoff events were identified from 2022-2024 using daily discharge (derived from stage-discharge relationships) and precipitation data collected from three rain gauges. Initially, runoff increased with degree of defoliation (2019-2021), however in 2022 there was a drastic increase in runoff (~40%) which was maintained through 2024 (~30%). These results suggest that catchment runoff was more significantly impacted as the defoliation event intensified and tree mortality began. To further identify the processes governing streamflow generation frequency discharge and precipitation analysis will be used to determine what fraction of runoff can be attributed to precipitation regime or spruce budworm defoliation/tree mortality. This long-term hydrological record of an on-going insect outbreak will provide critical knowledge to catchment and forestry managers, increasing our ability to predict hydrological changes in a landscape with increasing anthropogenic and environmental disturbances.