Glacierized catchments are among the most rapidly changing and visibly affected regions worldwide due to glacier retreat and the associated loss of a critical water resource. This alters streamflow patterns, yet the timing and specific parts of the hydrograph that experience the strongest changes remain less understood. While previous studies have focused on glacio-hydrological modelling or observations of a small set of catchments, this study leverages a comprehensive dataset of streamflow observations from approximately 600 glacierized catchments (10–1000 km²) worldwide. By integrating these streamflow records with geodetic estimates of glacier mass loss, we identify regions experiencing the strongest mass losses and the associated rates of glacier change. Consequently, we explore the spatial and seasonal patterns of streamflow change and identify when the strongest streamflow changes occur and how they vary regionally and globally. For gauging stations with long-term observations (>50 years), we aim to assess whether emergence of specific seasonal trends and changes can be detected. Our findings highlight significant regional variability in the timing of the strongest seasonal streamflow changes. In some regions, late-summer flows show the most pronounced changes in relative magnitude, while in others, spring flows are most affected. By pinpointing these critical periods and spatial variability of change, this study provides insights into the downstream implications of glacier mass loss on water availability and streamflow dynamics.