Traceability and Uncertainty in Moisture Monitoring of Built/Urban Green Infrastructures: A Critical Scoping Review

Urban green infrastructures (UGI), such as living walls and green roofs, are increasingly reliant on substrate moisture monitoring for irrigation control, performance assessment, and maintaining function under heatwaves, drought, and intense rainfall. In many instances, however, moisture 'measurement' is simply understood as a direct signal from a sensor, with limited consideration of traceability, calibration transferability, and dominant influence quantities (such as temperature, electrical conductivity/salinity, bulk density/packing or compaction, contact installation and substrate aging). In this focused critical scoping review, we map moisture-determination methods used in built/urban green infrastructure (GI) and conduct a rubric-based metrological appraisal of reporting quality and uncertainty handling. Specifically, we outline the main measurement approaches and assess published studies using a reproducible evaluation rubric covering measurand definition, measurement model, independent reference for calibration/validation (e.g., gravimetric sampling), calibration strategy, uncertainty treatment, and operational reporting for IoT deployment. The results indicate that metrologically critical information is often missing: many studies (2016 2025) do not report a traceable measurement chain (measurand definition, sensor principle, calibration approach, and reference/ground truth), and they rarely document how dominant influence quantities (e.g., temperature, bulk EC/salinity, bulk density/compaction, installation/contact effects, and media aging) were measured, controlled, or corrected. In addition, uncertainty is typically reported only through error metrics rather than through an uncertainty budget or sensitivity/propagation analysis; based on these findings, we propose minimum reporting requirements and a pragmatic uncertainty aware workflow for moisture monitoring in engineered substrates.