This paper explores how streamflow reanalysis responds to precipitation forcing errors across 671 catchments in the United States. For the Global Flood Awareness System v4.0 driven by European Centre for Medium-Range Weather Forecasts Reanalysis v5, each 1 mm increase in precipitation error causes a mean increase of 0.51 mm streamflow error. This response varies by catchments as humid regions amplify the increased errors up to 2.5 mm, but arid and snowy regions dampen or delay them by storage.