Latin America (particularly its tropical region) is rich in freshwater systems. Large river basins, lakes, freshwater wetlands, and reservoirs distributed throughout the region have facilitated the development of thousands of human settlements-with associated agricultural and industrial activities-and the harnessing of rivers for energy production. In addition, important segments of national and international rivers permit fluvial transportation of people and merchandise. The opening of the international Paraguay-Paran� Rivers Hydroway would expedite the increasing commercial traffic arising from the developing regional market, Mercosur. Freshwater systems also are sources of income from fisheries, aquaculture, and tourism. Latin America's extensive river basins, large numbers of lakes, and important freshwater wetlands (i.e., El Pantanal and Iber�) host a great number of fish species, amphibians, semiaquatic rodents, and reptiles, some of which-like the capybara (Hydrochoerus hydrochoeris) and yacar� (a type of Caiman latirostris), which are particular to this region-are important sources of income for local communities.
Tropical rivers in Latin America host about 1,500 species; in addition to their commercial value, these species are the basis for the yearly international Alto Parana river "dorado" fishing contest, an important tourist event. The wetlands also are stopover places for a number of bird species-especially waterfowl, which fly back and forth between the United States and Canada and Latin America. The longest waterfowl migration probably is that of the blue-winged teal (Anas discors), which nests as far north as 60�N in North America and winters south of 30�S, traveling a distance of more than 9,600 km.
Freshwater systems are potentially very sensitive to climate change (IPCC 1996, WG II, Section 10.3) and vulnerable to interannual fluctuations in climate, such as those associated with the ENSO phenomenon. Increased climatic variability is expected to have greater ecological effects than changes in average conditions. Associated flash floods and droughts would reduce the biological diversity and productivity of stream ecosystems (IPCC 1996, WG II, Section 10.6) and affect living conditions and welfare in flood-prone areas as well as in arid and semi-arid regions. Thus, monitoring of associated environmental variables is an urgent need.
Most Latin American countries, however, have inadequate hydrological and meteorological observation networks. Large, uninhabited areas have no surface observation systems, and the densities and operational practices of existing networks generally do not meet the recommended international and regional standards. As a result, records of variables that are important for the study of freshwater systems are scarce and suffer from incomplete areal and temporal coverage, particularly because of frequent closings of observation posts in recent decades. Under these conditions, water resources monitoring vis-�-vis climate change is very indequate. In fact, the 1992 Supplementary Report to the IPCC First Assessment Report (FAR) concluded that, although significant progress has been made in hydrological sensitivity analyses in developed countries, large gaps exist for less-developed countries.
About 35% of the world's continental waters (freshwater) are found in Latin America, but the distribution within and among countries is highly variable (see Annex D for data on water resources per capita and annual domestic and industrial water withdrawals). Many areas (e.g., northern Mexico, northeastern Brazil, coastal Peru, northern Chile) have great difficulty meeting their water needs. About two-thirds of Latin America is arid or semi-arid, including large portions of Argentina, Bolivia, Chile, Peru, northeastern Brazil, Ecuador, Colombia, and central and northern Mexico.
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