Traceable methods and dedicated facilities for the calibration of non-catching precipitation gauges.

As the approval by CEN proves, the report shows methods and technologies currently used by non-catching rain gauges and explores the calibration and accuracy issues of these instruments. Three different raindrop generators were developed, built and characterized in order to perform experiments and validations for the calibration of the rain gauges.

Model functions of non-catching precipitation gauges and input and influence parameters

For the first time an uncertainty budget for a quantity measured by a non-catching rain gauge was evaluated with metrological rigour. The report lists different model functions for different rain gauges technologies, and that makes it possible to evaluate uncertainty budget for a wide variety of non-catching gauge models.

Validation of calibration methods and uncertainty budgets

Three types of non-catching precipitation gauges were calibrated; a model for the calibration uncertainty of non-catching precipitation gauges was proposed and detailed. Further to the laboratory validation, field testing was performed at the experimental test sites of Payerne (CH) and Vigna di Valle (IT).

Standardisation related to non-catching precipitation gauges

The engagement with committees was constant throughout the project. Standard and regulatory activities were performed at the European scale, and therefore first addressed to CEN/TC 318 as an initial step towards further extension at the global scale (ISO/TC 113). CEN has agreements in force with ISO and the WMO in order to address the development of standards on similar topics, to avoid duplications.

The Working Arrangement between the WMO (where the GCOS Surface Reference Network is a part of GCOS which is a Study Group of WMO, undergoing same regulatory processes) and ISO, signed in 2008, explicitly aims to strengthen the development of International Standards and to avoid duplication of work on standards related to meteorological, climatological, hydrological, marine and related environmental data, products and services.

Also, the chair of CEN/TC 318 is an active member of ISO/TC 113 and will keep that committee aware and informed of the normative steps activated within CEN on this subject.

Wider impact from the project is expected on companies operating in the fields of hydro‑meteorological warnings, water resources management, flood control, and agriculture. These companies generally provide services based on the monitoring of hydro-meteorological variables (precipitation, flow rate, evaporation, etc.) and the processing of the related measurements to support end users’ decisions, even in real time, about the configuration of industrial systems including water diversions, dam overflows, weirs, hydropower turbines, etc. Due to their intrinsic features, non‑catching instruments require less maintenance, and the absence of mechanical and moving parts makes them more stable devices for field use, impacting on the required calibration and check intervals, and resulting in reduced maintenance costs for hydro-meteorological agencies and users. The use of calibrated non-catching type instruments to measure liquid precipitation would improve the management capabilities of the users, since decisions would be based on traceable measurements obtained at a lower operational cost than the present networks of catching-type instruments.

Based on a general lack of traceability and data quality in historical observations, the Global Climate Observing System (GCS) is preparing the creation of the GCOS Surface Reference Network (GSRN). During its first meeting the newly formed WMO Commission for Infrastructures approved the creation of the GSRN under its Decision 4.1.1(4)/1 (INFCOM-1), “Development of a draft implementation plan for the GCOS Surface Reference Network”. There, “a set of high‑quality long-term fiducial reference measurements of Essential Climate Variables (ECV) is recommended to enable future generations to make rigorous assessments of future climate change and variability. Non‑catching gauges will offer more reliable data and are relatively immune to maintenance and mechanical drifts and shocks, thus becoming a more robust candidate for long term data series recording. The calibration procedures and guidance developed by this project are therefore expected to benefit climate science through the GCOS and other similar initiatives, by enabling better environmental and climate data and analysis.

Non-catching instruments are suited to operation in unmanned meteorological stations, e.g. those far from urban settlements or in remote areas and in harsh environments. These remote stations are needed to monitor the whole territory of hydrological basins, whose headwater area is generally located in mountainous or impervious regions, in order to provide improved coverage and completeness of information about incoming precipitation. More reliable early warnings would therefore make it possible to promptly inform weather services, civil protection agencies and the general population about the risk of floods and especially flash floods, which evolve rapidly and have a strong potential for disruption. The accuracy of such data and information is vital for issuing effective and timely warnings, resulting in increased safety for citizens and extended lead time for warnings, with a potential to save lives and properties in case of extreme events.

Traceable methods and dedicated facilities for the calibration of non-catching precipitation gauges.

As the approval by CEN proves, the report shows methods and technologies currently used by non-catching rain gauges and explores the calibration and accuracy issues of these instruments. Three different raindrop generators were developed, built and characterized in order to perform experiments and validations for the calibration of the rain gauges.

Model functions of non-catching precipitation gauges and input and influence parameters

For the first time an uncertainty budget for a quantity measured by a non-catching rain gauge was evaluated with metrological rigour. The report lists different model functions for different rain gauges technologies, and that makes it possible to evaluate uncertainty budget for a wide variety of non-catching gauge models.

Validation of calibration methods and uncertainty budgets

Three types of non-catching precipitation gauges were calibrated; a model for the calibration uncertainty of non-catching precipitation gauges was proposed and detailed. Further to the laboratory validation, field testing was performed at the experimental test sites of Payerne (CH) and Vigna di Valle (IT).

Standardisation related to non-catching precipitation gauges

The engagement with committees was constant throughout the project. Standard and regulatory activities were performed at the European scale, and therefore first addressed to CEN/TC 318 as an initial step towards further extension at the global scale (ISO/TC 113). CEN has agreements in force with ISO and the WMO in order to address the development of standards on similar topics, to avoid duplications.

The Working Arrangement between the WMO (where the GCOS Surface Reference Network is a part of GCOS which is a Study Group of WMO, undergoing same regulatory processes) and ISO, signed in 2008, explicitly aims to strengthen the development of International Standards and to avoid duplication of work on standards related to meteorological, climatological, hydrological, marine and related environmental data, products and services.

Also, the chair of CEN/TC 318 is an active member of ISO/TC 113 and will keep that committee aware and informed of the normative steps activated within CEN on this subject.

Wider impact from the project is expected on companies operating in the fields of hydro‑meteorological warnings, water resources management, flood control, and agriculture. These companies generally provide services based on the monitoring of hydro-meteorological variables (precipitation, flow rate, evaporation, etc.) and the processing of the related measurements to support end users’ decisions, even in real time, about the configuration of industrial systems including water diversions, dam overflows, weirs, hydropower turbines, etc. Due to their intrinsic features, non‑catching instruments require less maintenance, and the absence of mechanical and moving parts makes them more stable devices for field use, impacting on the required calibration and check intervals, and resulting in reduced maintenance costs for hydro-meteorological agencies and users. The use of calibrated non-catching type instruments to measure liquid precipitation would improve the management capabilities of the users, since decisions would be based on traceable measurements obtained at a lower operational cost than the present networks of catching-type instruments.

Based on a general lack of traceability and data quality in historical observations, the Global Climate Observing System (GCS) is preparing the creation of the GCOS Surface Reference Network (GSRN). During its first meeting the newly formed WMO Commission for Infrastructures approved the creation of the GSRN under its Decision 4.1.1(4)/1 (INFCOM-1), “Development of a draft implementation plan for the GCOS Surface Reference Network”. There, “a set of high‑quality long-term fiducial reference measurements of Essential Climate Variables (ECV) is recommended to enable future generations to make rigorous assessments of future climate change and variability. Non‑catching gauges will offer more reliable data and are relatively immune to maintenance and mechanical drifts and shocks, thus becoming a more robust candidate for long term data series recording. The calibration procedures and guidance developed by this project are therefore expected to benefit climate science through the GCOS and other similar initiatives, by enabling better environmental and climate data and analysis.

Non-catching instruments are suited to operation in unmanned meteorological stations, e.g. those far from urban settlements or in remote areas and in harsh environments. These remote stations are needed to monitor the whole territory of hydrological basins, whose headwater area is generally located in mountainous or impervious regions, in order to provide improved coverage and completeness of information about incoming precipitation. More reliable early warnings would therefore make it possible to promptly inform weather services, civil protection agencies and the general population about the risk of floods and especially flash floods, which evolve rapidly and have a strong potential for disruption. The accuracy of such data and information is vital for issuing effective and timely warnings, resulting in increased safety for citizens and extended lead time for warnings, with a potential to save lives and properties in case of extreme events.