Executive Summary

This meeting of experts was organised to consider the establishment of a global hydrological network for climate. The specific objectives of this meeting were to determine user needs for a global hydrological network; identify products to be delivered by such a network and to develop a vision and a strategy for establishing an initial, end-to-end observing "system".

Although the focus was on climate-related hydrological variables, the participants fully realised the importance of these variables (and the consequent benefit of a global network) for other subject areas, including water resources monitoring and assessment, monitoring of the global water cycle, biodiversity issues, land-based sources of pollution, as well as coastal and agricultural applications. Among the key groups that are calling for such information are intergovernmental mechanisms such as the international environment conventions and agreements as well as regional bodies. The climate community, scientists involved in research and modelling, and policy analysts frequently cite the need for improved access to hydrological data and information in order to understand key environmental change processes, identify significant trends, assess variability, and develop informed responses.

The meeting identified existing networks, centres and mechanisms that could contribute to an observing network; and proposed an approach to implementation. The meeting was hosted by the Forschungsanstalt Geisenheim and the Deutscher Wetterdienst and attended by representatives of international agencies, organisations and programs active in hydrology observations.

Through presentations and plenary as well as breakout group discussions, the participants synthesised the driving policy and science requirements for global hydrological observations under five themes: improved climate and weather prediction; detection and quantification of climate change; assessment of the impacts of climate change; assessment of fresh water sustainability; and understanding the global water cycle. It was emphasised that these climate-related themes are also relevant to other issues, e.g. water resources management, agriculture and biodiversity, and thus the strategies for observation and data products need to be developed through close collaboration. Following a review of the major hydrological programs and activities as well as the present status in the observation of key hydrological variables^[1], the participants discussed the need and the strategy for ensuring the ongoing availability of systematic, comprehensive global hydrological observations and data products. An effective global system will consist of satellite and in situ measurements, and both ultimately depend on national implementation and support. Given the existing networks and data product centres, it was agreed that the most desirable approach is linking those currently active to obtain a maximum benefit and as a basis for further improvements. To this end, a Global Terrestrial Network for Hydrology (GTN-H) was proposed to complement terrestrial networks already established for permafrost, glacier and ecological observations. Among the existing hydrology networks and data centres, candidates were identified to address the needs for most of the key hydrological variables on a global basis. In addition, the participants defined the need for a scientific panel (Hydrology Observation Panel for Climate, HOPC) that would guide the implementation of GTN-H, advise on the selection of priority products, and ensure linkages with science programs that have observation components and needs. HOPC and GTN-H should be sponsored by the major international organisations with hydrology interests. The governance issues were addressed in a preliminary way. The meeting also defined initial global products for specific variables that are needed now and could be produced in the near future and identified lead agencies for these, and developed a list of early actions and opportunities that should be pursued in the near future.

The following specific recommendations were made:

1. A Global Terrestrial Network for Hydrology (GTN-H) should be established to meet the needs for global hydrological observations for climate. This network should build upon existing hydrology networks and data centres, hence serving as the hydrological complement of existing global terrestrial networks. Recognising, that a GTN-H could meet many other requirements for hydrology and water resources management including i.e. the characterisation of hydrologic processes and systematic regional and global hydrological observations, its terms of reference should address the needs of several regional and global programs in hydrology and water resources in addition to the climate requirements established at this meeting.

2. Potential GTN-H sponsors and participants identified at this meeting should be approached to obtain their endorsement and contributions.

3. A Hydrological Observation Panel for Climate (HOPC) should be established, with its major responsibility being to guide the development and implementation of GTN-H and to ensure its effectiveness.

4. HOPC should act in close cooperation with its sponsoring agencies, global observing systems (GCOS, GTOS, GOOS, WWW), institutions participating on behalf of the global observing systems, and global research programs (especially IGBP and WCRP); and the HOPC terms of reference should be developed accordingly.

5. HOPC and GTN-H should develop a plan for meeting the data and product requirements by the various application communities. This plan should take advantage of the initial product generation activities and interests of the participants (section 7.6). Early tangible and beneficial results should be an important goal in preparing this plan.

6. Near-future opportunities for the development of GTN-H should be vigorously pursued, including collaboration within CEOP.

7. The implementation of the recommendations should be undertaken by the sponsors of this expert meeting, i.e. GCOS, HWR/WMO and GTOS, with the interim assistance of TOPC.