A number of oral presentations of programmes relevant to GCOS and GTOS were delivered by participants in the meeting, as indicated in Annex 3.
Mr Cihlar described the work of the GCOS/GTOS Terrestrial Observation Panel for Climate (TOPC). He explained that the TOPC was in the process of revising the GCOS/GTOS Plan for Terrestrial Climate-related Observations and welcomed any comments that the panel members might have. He also presented the concept of a tier system. He explained that the system was developed primarily in relation to ecological variables, but the TOPC wanted to know if the concept was also applicable to hydrological variables. Details of the sampling procedure based on the tier concept are presented in Annex 4. The meeting discussed the tier concept and concluded that, with some modification it was applicable to hydrological variables.
Mr Kaczmarek presented his working paper on Hydrological Data in Global Climate and Terrestrial Observing Systems, which is attached as Annex 5.
Mr Stewart discussed the results of the Basic Hydrological Network Assessment Project (BNAP). This study was the first major attempt to analyse the current level of basic hydrological networks from a global perspective. For many years, hydrologists and water resources managers have relied on the network density criteria established arbitrarily by experts to determine the minimum size of the required networks. The inadequacy of hydrological networks was recognized at the 1977 United Nations Water Conference and in the resulting Mar del Plata Action Plan. It was noted that in most countries there were serious inadequacies in the availability of data on water resources, particularly in relation to ground water and water quality. Its recommendations included a call to improve networks and network densities.
In the BNAP study, the adequacy of hydrological networks has been evaluated on a global basis, using data supplied by 58 countries from around the world. “Basic” stations are those required for minimum water resources management, and are generally long-term stations monitoring unregulated flows. Results suggest that the highest station densities are found in small islands, hilly, mountainous, and coastal physiographic regions, in temperate climates, and in basins with 500,000 to 2,500,000 people. Ground water networks are the most dense based on physiography, climate, and population. Results vary considerably, however, even between basins with similar characteristics. Network adequacy was assessed in two ways. Firstly, application of current WMO density criteria indicates that water quality, evaporation, and sediment networks satisfy the minimum guidelines on average, while precipitation and discharge networks are lacking. Secondly, evaluation of “needed” densities, as reported by the participating countries, suggests that the ground water and water quality networks are adequate, with inadequacies apparent for the rest of the hydrological variables and all physiographic classes studied. Again, results vary considerably by country, hydrological variable, and physiography.
Overall, basic ground water networks appear to meet needs, while basic water quality, evaporation, and sediment networks are of questionable adequacy, and basic discharge, water temperature, and precipitation monitoring networks appear to be least adequate to meet minimum water management needs. The relative results obtained appear to be consistent with WMO's current density guidelines. Proposed revisions to the minimum hydrological network density criteria were also presented. For the specific results of the study, the reader is referred to the document The Adequacy of Hydrological Networks: A Global Assessment (WMO/TD - No. 740) by A. Perks, T. Winkler and B. Stewart.
Mr Rudolf described the Global Precipitation Climatology Centre (GPCC) which holds precipitation data sets from over 40,000 stations. He also reviewed a number of activities of the Centre and reported of their data products, such as gridded precipitation fields. The GPCC has developed a 2.5 degree by 2.5 degree gridded precipitation product for the world. They are working toward a 1 degree by 1 degree product. In response to a question regarding the feasibility of developing a .5 degree by .5 degree product, Mr Rudolf explained that it would be possible for some regions, but in other regions there were insufficient data.
Mr Grabs informed the meeting of the mandate and activities of the Global Runoff Data Centre (GRDC) whose holdings embrace at present daily and monthly data on river flow from over 3300 stations worldwide. The key objective of GRDC is to ease the access of WMO Members to data necessary for implementation of water resources projects of global or regional character. The GRDC interacts with national and regional hydrological data centres, and with other global-scale centres. Among the recent activities of GRDC is the study of a fluxes of freshwater into oceans, including a sensitivity analysis in order to determine the minimum number of rivers that need to be monitored.
Mr Gustard presented information on the UNESCO-IHP Project on Flow Regimes for Experimental and Network Data (FRIEND). Although many of the IHP activities are oriented towards research rather than operational hydrology, this particular UNESCO-IHP project requires the collection of large sets of hydrological data. The current FRIEND database contains daily discharge data from a number of small catchments which should be relatively free from anthropogenic influences. The project that started in 1986 in Western and Northern Europe, where it has now a data base of around 4,000 stations, now has a number of other regional implementations in other continents; the most recent development being the Hindu Kush - Himalayan FRIEND.
Ms Enderlein described the activities of the Global Environment Monitoring System - Water (GEMS-Water), implemented by WHO with the support of UNEP, where data from 80 rivers are collected and altogether 50 water quality variables are considered. In particular, she mentioned a recent project designed to provide a GEMS/WATER contribution to the global register of river inputs to the oceans (GLORI).
Mr Kundzewicz reviewed global-scale issues where hydrological data are necessary and compiled a list of global data centres, which is attached as Annex 6 to this report. He also elaborated on alternative versions of the statement of the problem of building an initial observing system for hydrological data. Two possible strategies were presented to develop sets of hydrological stations for purposes of global observing systems. They differ by the point of departure, being either the needs of observing systems (scientific approach) or the availability of existing networks (practical approach). The former strategy would estimate the network necessary to obtain hydrological data fulfilling the goal of the global observing systems without being preoccupied, initially, with the existing network. In the latter approach, the assumption is taken that only existing sites are available and the initial global network is defined from existing data bases, such as GRDC.
