Most Global Gauging Stations Present Biased Estimations of Total Catchment Discharge

Stream gauging stations provide critical streamflow measurements for hydrological applications; however, they may not accurately capture total catchment discharge due to unmonitored regional groundwater flow. Here, we evaluate the effectiveness of streamflow data from gauging stations worldwide to represent total catchment discharge through a modified hydrological model that includes baseflow signatures to constrain groundwater flow processes. We find that approximately 70% of gauging stations present biased estimations of total catchment discharge (bias >10%). This result implies that hydrology‐related processes may not be fully understood, and misleading conclusions may be drawn owing to the low streamflow measurement effectiveness. By influencing subsurface hydrological processes, catchment factors, including catchment area, topography, climate, and geological features, are linked to the effectiveness of streamflow measurements. Our findings highlight the importance of accurate streamflow measurement effectiveness for obtaining a reliable understanding of catchment hydrological processes to support sustainable water resource management. Plain Language Summary The outflow of water from catchments plays a critical role in supporting downstream ecosystems and human society. This catchment outflow includes surface and subsurface discharge. However, a portion of the subsurface discharge may not directly flow into river networks and thus remains unaccounted for in streamflow records at gauging stations. The extent to which these unmonitored subsurface flows exist across catchments and their contribution to the total catchment discharge remains unknown. To address this knowledge gap, we have developed a novel method that simulates the movement of both surface and subsurface flows, enabling us to evaluate the representativeness of streamflow records in capturing the total catchment discharge. Our findings indicate that approximately 70% of gauging stations worldwide inadequately capture the total catchment discharge (bias >10%). This observation highlights the importance of unmonitored subsurface discharge as a significant component of catchment water yield. Such insights enhance our understanding of catchment hydrological processes, supporting the development of sustainable water resource management strategies. Key Points A modified hydrological model was developed by including baseflow signatures to constrain groundwater flow processes Approximately 70% of ga