This section is divided into five parts: first a brief description of the terrestrial observation system design, then sections on three components of terrestrial systems, namely the hydrological, cryological, and ecological systems. Within each of those areas this report gives a brief overview of the state of existing observation systems, identifies some issues and contains some specific recommendations. Finally there is a section on issues and recommendations that cut across all three systems.
An Overview of Terrestrial Observation System Design
Emerging global environmental problems with strong terrestrial impacts, drivers or linkages, have created a need for a robust, flexible and cost-effective terrestrial observing system. The requirement to span a wide range of space scales and temporal resolutions led the joint GCOS and GTOS TOPC to a hierarchically based sampling strategy called GHOST (Global Hierarchical Observing Strategy) (GCOS 1994, ICSU/UNEP/FAO/UNESCO/WMO 1996). The strategy is outlined in the GHOST brochure and described in detail in the GCOS/GTOS Plan for Terrestrial Climate-related Observations (GCOS, 1995b). The proposed system has five tiers, ranging from a small number of locations where highly integrated, detailed data are collected with a high time resolution, to a large number of locations where very simple data are collected less frequently. There are intermediate tiers with specific roles and attributes. The hierarchical structure, in conjunction with the use of models and remote sensing, is believed to be the only affordable approach that allows global coverage with the necessary levels of complexity, spatial and temporal resolution. Although the hierarchical concept arose from the work of a land-based group, the basic idea is applicable with appropriate modifications to freshwater and cryospheric systems as well. It is not intended to be applied as a rigid formula. The variables in GHOST are designed to be a 'minimum package' to achieve given objectives. They therefore fall into question-based clusters, which span the hierarchical tiers.
The Hydrosphere
The hydrological cycle is intrinsic to the Earth's climate system. The process by which water, in all its phases, moves through the atmosphere and moves to and from the various repositories on the Earth's surface are intermeshed with the earth's energy budget. The availability of water controls the abundance and distribution of vegetation and biological productivity. One of the most significant results of climate change will be the shift of regional hydrological regimes and changes in the availability of water resources. Our ability to characterize the current state of the hydrological cycle, globally and regionally, and to make quantitative predictions as to the nature of potential changes depends on consistent information of appropriate quality and adequate spatial and temporal coverage. Such hydrological data sets are currently lacking for many regions of the earth.
Improvements are occurring for some hydrological observations. New and more sensitive sensors and methods are being developed so that data can now be obtained that were previously impossible to collect. Flow data, water quality data and the measurement of evaporation have benefited in this way. Weather radar data have provided a better depiction of local and regional rainfall distributions. A number of global centers have been established to collect hydrological data and make them available to users, for example, the Global Runoff Data Centre (GRDC), Koblenz, Germany; the GEMS (Global Environmental Monitoring System) Collaborative Centre for Water Quality, Burlington, Canada; the Global Precipitation Climatology Centre (GPCC), Offenbach, Germany; and the Global Lake and Catchment Conservation Database, Dorking, UK. These and similar regional data sets, such as those being developed by the FRIEND project of the International Hydrological Programme/United Nations Educational, Scientific and Cultural Organization (IHP/UNESCO), are being used in hydrological research projects. There are a number of large basin research projects underway such as the GEWEX-GCIP and the Large Scale Biological-Atmosphere Experiment Amazonia (LBA) experiment that will provide, not only a better understanding of hydrological processes, but basic data that can be used by the global observing systems.
Most countries have routine operational observing systems for national purposes, although these data are not always readily available outside the boundaries of the country collecting the data, nor are they necessarily collected or available in a form suitable for a global observing system. Recently, establishment of a World Hydrological Cycle Observing System (WHYCOS) has begun to collect near real time discharge data from major rivers. WHYCOS has started on a regional basis in the Mediterranean region and southern Africa. Eventually it is planned to be a global operational system of over 1000 stations.
While some observations are being improved, there are numerous problems. Due to the difficulty of measuring many components of the hydrological cycle, measurement errors and gaps in networks exist in parts of the world for many critical variables. The data are rarely normally distributed and they contain many unexplained outliers. A lack of standard methods leads to uncertainties and inconsistencies in the data. For example, there are 60 types of precipitation gages in use around the world making it extremely difficult, if not impossible, to detect systematic changes in precipitation. Densities of networks recommended by WMO are not being met in many parts of the world, particularly in Africa. Moreover, the national hydrological services in many parts of the world are degrading. This is expected to continue in both the developing world and the developed world. Also some countries refuse to make their data available outside their own borders. Other data that are available simply do not make their way to data centres where they could be readily accessed.
Many of these problems will not be solved in the short term, but the global observing systems can help by providing overall planning and coordinating mechanisms. Further, it is critical that the WWW take a lead to assure the standardization of measurements, such as those for precipitation.
Issue: There are large gaps in the coverage of critical hydrological observations. This situation is likely to become worse in the near future as many systems continue to degrade.
Recommendation T1. WMO through the HWRP should periodically contribute to an assessment of the state of the hydrological networks.
Issue: There are significant problems associated with the availability of hydrological data. Of particular importance is the refusal of countries to share data outside their national boundaries.
Recommendation T2. Given the lack of availability of many types of hydrological data GCOS and GTOS should immediately contact the FRIEND office to take advantage of the offer of this programme office to help make their data available to a wider community. Making such data available on the Internet should encourage others to make their data available as well. In addition GCOS and GTOS should establish Internet links to the vast amount of United States Geological Survey (USGS) data that is already available.
Issue: There is a lack of standardization of sampling devices in use for many hydrological measurements.
Recommendation T3. In the context of sampling devices for hydrological measurements WMO should continue to support inter-comparison studies and work towards standardization to the maximum extent possible.
