The new WMO Expert Team on Hydrometry and its mandate

The new WMO Expert Team on Hydrometry and its mandatePrepared for EGU 2025 in Vienna (April 2025) and HS1.2.1 Session on Innovative Technologies and Approaches in Hydrological Monitoring Libor Ducháček, Salvador Peña-Haro, Elizabeth Jamieson, Tommaso Abrate, Jérôme Le Coz The World Meteorological Organization (WMO) seeks to provide the framework for international cooperation to advance meteorological, climatological, hydrological, and related environmental services, to improve well-being of all. Within are several working groups and expert teams like the newly established Expert Team on Hydrometry (ET-Hydrometry). The Expert Team on Hydrometry evolved from Project X (the short name for the WMO group titled the Assessment of the Performance of Flow Measurement Instruments and Techniques), which was established in 2008 and focused on assessing flow measurement instrumentation and measurement methodologies, through the development of literature reviews, the collection of data and reports, intercomparison events and activities, etc., and to make the relevant outputs (reports, guidance, best practices, software, etc.) available to Hydrological Services around the world. In 2024, the Expert Team on Hydrometry (ET-Hydrometry) was established (to replace Project X) under the direction of the Chair of the Standing Committee for Measurement Instrumentation and Traceability (SC-MINT), under the WMO Commission for Observation, Infrastructure and Information Systems (INFCOM). The overall objectives of ET-Hydrometry remains the same as the former Project X, but with an expanded scope beyond flow measurement instrument and techniques to encompass a broad number of hydrometric (water level and flow) activities and parameters. As well, with the growing need to support at a practical and operational level the implementation of new innovative technologies (particularly those coming from the WMO HydroHub initiative), there is an important role for ET-Hydrometry to play with establishing assessment methodologies and technology transition pathways for the validation and adoption of new technologies and methods. Furthermore, ET-Hydrometry will encourage and promote guidance material and standardized approaches that are freely available and accessible to all wherever possible. Both established and innovative hydrometric instrumentation and methodologies are to be considered, including lower cost and lower tech alternatives to traditional approaches. In 2025, the primary objective of the expert group is to finalize guidance for organizing acoustic Doppler current profiler (ADCP) regattas and similar hydrometric intercomparison events. These events are highly valuable to National Hydrological Services (NHSs) as they facilitate the mutual comparison and verification of commonly used instruments for streamflow measurements under natural (field) conditions. These intercomparison events also aim to foster collaboration and encourage the exchange of technical knowledge and fieldwork expertise among participants. The results from these events can also provide valuable datasets for the advanced analyses of instrument performance and determining discharge measurement uncertainty.