Fresh water comprises a mere 2.5 percent of total water on Earth. Approximately 70 percent of the already small percentage is frozen in glaciers and permanent snow cover, and nearly all of the remaining 30 percent is ground water, largely a non-renewable resource. Renewable fresh water, mainly from the cycle of precipitation and evapotranspiration, is only 0.13 percent of global fresh water (see figure 1 below). The limited availability of usable freshwater is further aggravated by the uneven global distribution, as exemplified by the water-rich Great Lakes on the US-Canada border or the dry Saharan Desert in Africa. Although supplies are small and disproportionate, fresh water is essential to sustain terrestrial life.

Most communities are centred around freshwater sources, and a change in water accessibility can force people and animals to relocate. Unsustainable water use has accelerated, as evidenced by falling water tables, and the desiccation of lakes, rivers, and streams (Postel 2003).

Solutions to increasing demand on this finite freshwater supply by agriculture, industry, and other human activities are very difficult to find, especially when the natural global water cycle is complex and not yet entirely understood. The international community is striving to identify long-term answers and solutions. Chapter 18 of Agenda 21 was dedicated to water, 2003 was named the Year of the Freshwater by the UN General Council, and in March 2003, the 3rd Water Forum was held in Japan.

From these and additional conferences, policy-makers, scientists, and others have agreed that access to timely and coherent data is essential to the future of usable global water. In developing countries, water data may exist but have not been published or evaluated. Essential information is often not gathered because of funding or policy priorities. In developed countries, such as the United States, Canada, and in Europe, scientists have collected various climate data, including precipitation. In such countries, water data are more readily available, although gaps still exist. Less data are being collected for variables such as biogeochemical transport from land to ocean and evapotranspiration, which is hard to measure. While data collection progresses, ongoing discussions continue concerning the best practices and method standardization.

Hydrology in TEMS

The TEMS hydrology module has been developed to facilitate access to hydrology relevant data. The module contains ten core variable relevant to hydrology and provides links to data holders and major institutions involved in terrestrial fresh water issues.

Figure 1: Global distribution of water (reproduced with the kind
permission of Ramsar)

Comments on improving the Hydrology module, the TEMS website, and GTOS are welcome (gtos@fao.org).