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Hydrology Network (GTN-H)
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Focal point: Wolfgang Grabs

Globally integrated hydrological observations are the backbone for improved water management in the light of global change. GTN-H activities aim to enhance data accessibility and product development for a large variety of users.

Increasing the quality and consistency of data, as well as improving the understanding of global water processes, is essential in developing more accurate global and regional water balance models. This information is vital to manage variability and change in hydrological regimes, to assess the changing availability of water resources, and to improve forecasting accuracy of hydrological extremes.

Water cycle (source Ramsar)

GTN-H partners

The Global Terrestrial Network for Hydrology (GTN-H) is the result of the joint efforts of the WMO Hydrology and Water Resources (HWR) Department, the Global Climate Observing System (GCOS) and the Global Terrestrial Observing System (GTOS). GTN-H comprises existing networks, global databases and global data product centres, and is based around a Coordination Group that includes:

1. Global Runoff Data Centre – GRDC (BfG, Germany, under the auspices of WMO);

2. Global Precipitation Climatology Centre – GPCC (DWD, Germany, under the auspices of WMO);

3. Global Environmental Monitoring System – Water – GEMS/WATER (UNEP; Environment Canada); and
4. Complex Systems Research Centre (University of New Hampshire, USA).

With the successive identification of participating partners, the core group is expanding.

GTN-H objectives and activities

Developing and improving the availability of hydrological data and information required to address global and regional climate, water resources and environmental issues is a prime objective of GTN-H. Benefits will include: improved weather and climate prediction; hydrological characterization to detect climate change; ability to predict the impacts of change; and an understanding of the global water cycle in an integrated context of weather, water and climate. Other benefits will be the improved assessment of freshwater availability and variability, and the greater understanding of large-scale hydrological processes.

Central to achieving these objectives is the development of global-scale data products. A major area of activity within GTN-H aims to develop and implement improved approaches and tools for data collection, access and management to support GTN-H objectives, and here GTN-H is a key partner in implementation of the Integrated Global Water Cycle Observation (IGWCO) theme of the IGOS partners.


GTN-H progress in the last biennium included:
1. draft definition of hydrological metadata standards, based on the WMO core metadata standards (in collaboration with GRDC);
2. a prototype online near-real-time river gauge stations data system;
3. access to a first-guess global gridded precipitation product (courtesy of GPCC);
4. online access to the global water quality database of GEMS/Water;
5. second edition of the estimation of freshwater fluxes to the ocean (in collaboration with the University of New Hampshire and GRDC);
6. establishment of the GTN-H Web site and creation of an inventory of hydrological data and product sources (in collaboration with Environment Canada and the University of New Hampshire); and
7. contribution to the Implementation Plan for the Global Observing System for Climate in Support of the UNFCCC and the implementation plan of GEOSS.

Coordination meeting

The GTN-H Coordination Panel met in Koblenz, Germany (4–5 July 2005) to review key GTN-H projects; to identify additional networks; to develop products and plans relevant to global aspects of hydrology; and to address the need for improved availability and access to global hydrological data, information and products to support a wide range of climatic and hydrological objectives. The tasks and recommendations that emerged from the meeting included:

1. linking to the Arctic and oceanographic communities regarding river runoff into oceans data;
2. designate responsibility for the global harmonization of systematic observations of water vapour;
3. endorse support to the planned NASA/ESA surface water interferometry mission(s);
4. identify datasets (in situ and satellite) and research groups to be included in an international data centre for lakes and reservoirs;
5. coordinate the development of standard observational practices for hydrological variables;
6. ensure relevancy to GEOSS; and
7. ensure collaboration and synergy with GTOS-TEMS, through the hydrology module.

The figure below shows the current development of GTN-H along the identification of key partners for the ten selected variables to be covered by GTN-H.

Core Functions

The core function of GTN-H include:

1. provide users with timely access to global hydrological data and meta-data;

2. generate relevant products (including global-scale data products) and related documentation in a time frame and of a quality that is required by users;

3. promote method standardization and the use of 'best' practices (including policies, quality control, data formats, coding and transmission);

4. promote and facilitate free and unrestricted exchange of data and products within the existing framework;

5. Promote data integration, including both multiple platform observations and cross-network data;

6. evaluate adequacy of networks;

7. monitor and evaluate GTN-H performance;

8. contribute to identifying the key observational requirements of GTN-H, including requirements for satellite observations;

9. provide support for capacity-building.


The hydrology project will:

1. develop a joint map product on data availability (near real time and historical);

2. develop a state of the system map product;

3. establish tools (e.g., procedures) for data mining and standardized archiving;

4. produce data and analysis products, including gridded runoff/discharge fields, BGC fluxes to the oceans, and surface storage fluxes.

Hydrological variables

TOPC also selected 10 hydrological variables that are relevant to climate change. These are:
1. Surface water discharge; 2. Surface water storage fluxes; 3. Groundwater storage fluxes; 4. Precipitation; 5. Evapotranspiration; 6. Relative humidity; 7. Soil moisture; 8. Snow water equivalent; 9. Biogeochemical transport from land to ocean; 10. Sediment load at large river mouths

Hydrology Networks

Three major networks and global databases have been established by international organizations:
The Global Runoff Data Centre (GRDC)
The Global Precipitation Climatology Centre (GPCC)
The Global Environment Monitoring Centre on Water Quality (GEMS).

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© FAO   ::   Global Terrestrial Observing System - GTOS   ::   15 January 2005