There is a critical need for improved availability and access to global hydrological data, information and products for climate and hydrological research and applications in order to quantify key environmental change processes, identify significant trends, assess variability and develop response strategies.
The Terrestrial Observation Panel for Climate (TOPC), sponsored by the Global Climate Observing System (GCOS) and the Global Terrestrial Observing System (GTOS), identified ten hydrologic variables of importance to climate change monitoring in the GCOS/GTOS Plan for Terrestrial Climate-related Observations, version 2.0 (GCOS-32), and the Report of the GCOS/GTOS Terrestrial Observation Panel for Climate, fourth session (GCOS-46) (http://www.wmo.ch/web/gcos/gcoshome.html), as follows:
Seven variables are primarily of hydrologic concern - surface water discharge, surface water storage fluxes, groundwater storage fluxes, precipitation, evapotranspiration, relative humidity, and transport of biogeochemical materials from land to ocean;
Two other variables - soil moisture and snow water equivalent - have important hydrological dimensions; and
Water use, arising from socio-economic causes, is critical to better assess the impact of climate change on water resources.
TOPC also observed that there is no single entity that serves as a global or regional data centre for the above variables. Thus, the assembly of an adequate global information base will be a significant challenge.
In response, the World Meteorological Organization (WMO) Hydrology and Water Resources (HWR) Department, GCOS, GTOS, and TOPC organized an expert meeting in June 2000, hosted by the Deutscher Wetterdienst in Geisenheim, Germany to establish a global hydrological observing network for climate. The full Geisenheim report (WMO/TD-No. 1047) can be viewed at: http://www.wmo.ch/web/homs/geisenheim.pdf.
The outcome was a proposal for the establishment of a Global Terrestrial Network - Hydrology (GTN-H) which will consist of existing networks ("network of networks"), global databases and global data product centres, capturing the ten key hydrological variables mentioned above. The main objectives for the network were to:
Respond to urgent information requirements with regard to climate prediction, impacts and adaptation, including the characterization of hydrological variability to detect climate change;
Assess water sustainability as a function of water use versus water availability; and
Improve understanding of hydrological processes.
A summary of other recommendations includes:
1. 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;
2. HOPC should act in close cooperation with sponsoring agencies, participating organizations, global observing systems (GCOS, GTOS, Global Ocean Observing System (GOOS), World Weather Watch (WWW)) and global research programmes, especially the International Geosphere-Biosphere Programme (IGBP) and the World Climate Research Programme (WCRP);
3. Near-term goals should include developing a plan for meeting the data and product requirements of the various applications-oriented communities and pursuing collaboration, such as with the Coordinated Enhanced Observing Period (CEOP);
4. The sponsors of this expert meeting, i.e., GCOS, HWR/WMO and GTOS, should undertake the implementation of the recommendations, with the interim assistance of TOPC.
