Monitoring visibility gaps in global river water-quality archives: a basin-scale framework for environmental...

In situ monitoring is fundamental to environmental management, yet global assessments often rely on open archives that reflect monitoring visibility rather than monitoring presence. Here we harmonized GRQA and GlobSalt to 16,397 HydroBASINS level-6 basins for 2010-2020 and quantified visibility using coverage, intensity and continuity. The combined open inventory contains records in 2487 basins (15.2%), leaving 13,910 basins without an open record. To support management prioritization, we ranked unrecorded basins using an exposure proxy derived from upstream population and urban land fraction. This identified 696 exposure-screened hotspot basins that account for 22.7% of global basin population and 17.2% of basin GDP. Open-archive coverage is socioeconomically uneven: the visible 15.2% of basins represent 39.2% of population and 52.0% of GDP. Targeting the top 100 unrecorded basins captures 30.4% of hotspot population and 35.2% of hotspot GDP, about 40-47 times the random expectation. Comparisons with national datasets in China, the United States and England show that missing open records can reflect either monitoring gaps or open-data gaps, implying different management responses. The framework provides a reproducible basis for river-basin monitoring design, data mobilization and environmental management across jurisdictions.