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The Global Terrestrial Network for Rivers (GTN-R)

Official website: GTN-R

Contact: Ulrich Looser, Global Runoff Data Centre

Today, many countries operate national near real time water level or river discharge transmission schemes. Increasingly, countries publish their data on the sites of their individual national hydrological services (NHS). Though this is an important step forward, the diversity of hydrological data sources is still quite heterogeneous. As a consequence, the Global Runoff Data Centre (GRDC), hosted by the Federal Institute of Hydrology (BfG), Germany, has launched the Global Terrestrial Network for River Discharge (GTN-R), which aims at improving access to harmonized near real-time river discharge data that captures the freshwater influx into the world’s oceans.

The GRDC is the digital world-wide repository of river discharge data and associated metadata, and is mandated by the World Meteorological Organization (WMO). Its overall objective is to serve – on a long term basis – as a facilitator between providers and users of river discharge data in support of the water and climate related programmes and projects of the United Nations (UN), their specialised agencies and the scientific research community. For almost 20 years, GRDC has been operating a database of historic discharge data.

Although many countries publish water level or river discharge data on the internet, it sill remains a tedious task to draw together all information needed for global assessments and models. From a global perspective, the diversity of data sources is quite heterogeneous. Therefore, the Global Terrestrial Network for River Discharge (GTN-R) has been developed. In April 2005, the Secretary General of the WMO, Michel Jarraud, sent a letter to 82 WMO Member States, asking them for support in the implementation of GTN-R as well as for the provision of near real time river discharge data. He reminded Member States that GCOS had developed a set of recommendations on actions in its Implementation Plan (IP) for Global Observing Systems in Climate in support of the United Nations Framework Convention on Climate Change (UNFCCC) (finalized in 2004), including an action related specifically to the creation of the GTN-R as a baseline network of around 450 river gauging stations around the world that should provide near real-time daily discharge data. The total number of stations is changing constantly in the course of discussions with the different NHS about suitable stations. In 2006, GDRC was contracted by the Joint Research Centre (JRC) of the European Commission to provide a service similar to GTN-R on a European scale, in support of the European Flood Awareness System (EFAS). Analogous to GTN-R, the associated project was called European Terrestrial Network for River Discharge (ETN-R), and its operations were planned to be copied for the GTN-R.    

Past and recent activities of GTN-R

GCOS-ECVs: River Discharge, (Water Use, Lakes, Soil Moisture) (please see GTOS-56, and GTOS-59)

GRDC is actively working in close cooperation with the Global Terrestrial Network for Hydrology (GTN-H), and delivers data for long-term freshwater fluxes into the world’s oceans, long-term mean river discharges, and global composite runoff fields. GTN-R serves as the GCOS baseline river discharge network and is the basis for future versions of the GRDC product ’Long-term mean annual Freshwater Surface Water Fluxes into the Worlds Oceans’. Additionally, the GDRC is cooperating with the UN GEMS/Water Programme Office of UNEP/DEWA through sharing data for joint stations for biogeochemical flux computations, and has contributed GIS map layers of the major rivers of the world, which have been discharge weighted to the WHYMAP project that is mainly sponsored by UNESCO and the Federal Institute for Geosciences and Natural Resources (BGR) in Germany.

Future plans

The role of river discharge is very important in driving the climate system, as the freshwater inflow to the world oceans may influence the thermohaline circulation. Statistical properties of river discharge are seen as an indicator for climate change and variability, as they reflect changes in precipitation and evapotranspiration, and are also influenced by land cover on a long-term scale. River discharge data is required for the calibration and validation of climate and impact models, trend analyses, and socio-economic investigations.

As the success of GTN-R is mainly dependent on the regular provision of near real-time river discharge data from reference stations operated by NHS's, GRDC and GCOS have to make sure there is a continuous cooperation between all organizations that are able to assist in providing access to the available data for a successful GTN-R. Monthly observations of river discharge are generally sufficient to estimate continental runoff into the ocean, although daily data are needed to calculate the statistical parameters of river discharge, e.g. for impact analyses of extreme discharge. Besides the application in climate models, river discharge measurements are extremely important with respect to global water resources assessments as well as integrated water resources management including coping with floods and droughts. Therefore, the cooperation between GTN-R and GTN-H needs to be maintained on a long-term basis.