Long-term impact and legacy

SoMMet established and compared primary-level reference methods for determining soil water and moisture content. The project also developed portable transfer standards, implemented and tested calibration facilities, and evaluated commercial point-scale soil moisture sensors against traceable reference values.

These capabilities remain available at the participating institutes and can support calibration services, instrument evaluation, measurement comparisons and further research. Measurement systems and approaches developed during SoMMet were also taken up in the GrainMet project, extending their application to moisture and water-content measurements in plant-origin bulk materials.

Together, these developments help preserve the technical knowledge and measurement infrastructure established during SoMMet beyond the duration of the project.

For cosmic-ray neutron sensing, SoMMet characterised commercially available detector types in reference neutron fields, evaluated their response functions and associated uncertainties, and benchmarked neutron-transport models and digital twins. The project also developed practical guidance for calibrating CRNS systems under outdoor conditions.

These results can support existing and future CRNS networks by helping users to compare instruments, understand differences in detector response and improve calibration and validation procedures. The harmonisation and data-fusion approaches developed by the project can also support the comparison and combination of point-scale measurements, CRNS observations and satellite products.

Reliable long-term observations nevertheless require appropriate maintenance, site-specific calibration, corrections for atmospheric and environmental influences, quality assurance and documented uncertainty evaluation. SoMMet provides a technical foundation for these activities rather than a universally applicable or maintenance-free measurement solution.

More reliable and comparable soil moisture information can support irrigation planning, agricultural drought assessment, flood-risk evaluation and the management of soil and water resources. SoMMet contributed by improving the metrological basis of soil moisture measurements and by developing approaches for harmonising and combining observations obtained at different spatial and temporal scales.

The project's methods can help users determine whether measurements are representative of a particular field, catchment or management area. They can also support the integration of point-scale sensors, CRNS systems and satellite observations into agronomic and hydrological decision-support systems.

Benefits such as reduced water consumption, improved crop yields or lower operating costs were not directly evaluated within SoMMet. Achieving such benefits will depend on local validation, appropriate measurement infrastructure and the practical implementation of the project's methods by operational users.

Soil moisture is recognised by the Global Climate Observing System (GCOS) as an Essential Climate Variable because of its importance for interactions between the land surface and the atmosphere, the terrestrial water cycle, vegetation and climate.

The GCOS Surface Reference Network (GSRN) is being developed to provide long-term reference-quality surface observations with metrological traceability and defined uncertainties. Its initial implementation focuses on surface temperature and precipitation, while a plan for incorporating additional Essential Climate Variables is also envisaged.

If soil moisture is included during the future development of the network, the reference methods, uncertainty approaches and harmonisation procedures developed by SoMMet could provide relevant technical foundations. The project's results may also support other climate-observation initiatives seeking more traceable and comparable soil moisture information.

SoMMet's results remain openly available through the project website and the SoMMet Zenodo community. They include the Final Public Report; eight public deliverables, three of which are good-practice guides; peer-reviewed publications; open reports and datasets; and training recordings and presentation materials.

Continued access allows researchers, calibration laboratories, instrument manufacturers, observation networks and other users to apply, evaluate and further develop the project's methods. It also supports training and knowledge transfer beyond the original consortium.

SoMMet results can furthermore inform the continuing development of standards and technical guidance, including potential future contributions to the WMO Guide to Instruments and Methods of Observation (WMO-No. 8). Any formal incorporation will depend on the technical evaluation and approval procedures of the responsible organisations.