Towards operational joint river flow and precipitation ensemble verification: considerations and strategies given limited ensemble records

•Precipitation and river flow verification must be joined-up and physically-based.•Multi-scale analysis (national, regional, and catchment) adds relevant information.•Sampling uncertainty reduced by pooling river flow data on catchment area.•Percentile precipitation thresholds allow extremes to be captured when they occur.•Varying effect of observation error on verification metrics influences interpretation.