The brokering approach empowering the WMO data space for hydrology
Authors: Boldrini Enrico , Mazzetti Paolo , Papeschi Fabrizio , Roncella Roberto , Olivieri Massimiliano , Otieno Washington , Chernov Igor , Pecora Silvano , Nativi Stefano 
Published: February 2023

WMO is coordinating the efforts to build a data space for hydrology, called the WMO Hydrological Observing System (WHOS).&#160;Hydrological datasets have intrinsic value and are worth the enormous human, technological and financial resources required to collect them over long periods of time. Their value is maximized when data is open, of quality, discoverable, accessible, interoperable, standardized, and addressing user needs, enabling various sector users to use and reuse the data. It is essential that hydrological data management and exchange is implemented effectively to maximize the benefits of data collection and optimize reuse.WHOS provides a service-oriented framework that connects data providers to data consumers. It realizes a system of systems that provides registry, discovery, and access capabilities to hydrology data at different levels (local, basin, regional, global). In 2015, the World Meteorological Congress supported the full implementation of WHOS, which is currently publicly available at https://community.wmo.int/activity-areas/wmo-hydrological-observing-system-whos, along with information for both end users and data providers about how to use and join it.End users (such as hydrologists, forecasters, decision makers, general public, academia) can discover, access, download and further process hydrological data available through WHOS portal by means of their preferred clients (web applications, tools and libraries).Data providers (such as National Meteorological and Hydrological Services - NMHSs, river basin authorities, private companies, academia) can share their data through WHOS by publishing it online by means of machine-to-machine web services.The brokering approach powered by the Discovery and Access Broker (DAB) technology enables the interoperability between data providers&#8217; services and end users&#8217; clients. A mediation layer implemented by the DAB brokering framework mediates between the different standard protocols and data models used by both providers and consumers to seamlessly enable the data flow from &#160;heterogeneous data providers to the clients of each end user.In parallel, WHOS experts are working in constant collaboration with the data providers to support the implementation of the latest standards required by the international guidelines (e.g., WaterML2.0 and WIGOS Metadata Standard), optimize the data publication and improve the metadata and data quality.The WHOS Distance Learning course has been successfully conducted; attenders from NMHSs were provided updated information and guidelines to optimize their hydrological data sharing. The course is currently being translated into Spanish to carry out it for Spanish speaking countries in 2023.WHOS is a hydrological component of WMO Information System (WIS), which is currently in its pilot phase. WHOS and WIS Interoperability tests are currently being piloted and expected to end in 2023. The aim of this interoperability is to promote smooth data exchange between Hydrology community and the wider WMO community. Finally, hydrological data shared through WHOS will be accessible to general WIS users (all piloted programmes, including climate through OpenCDMS, and cryoshere) and at the same time WHOS users will make use of observations made available by WIS.