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Watersheds of the world: Ecological value and vulnerability

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Map 1: Primary watersheds
(736 KB)
This global analysis includes the world's largest transboundary watersheds and other small basins that a representative of a particular geographic area. Only permanent rivers are included.

Map 2: Freshwater fish species and endemism
(783 KB)
Some 27 watersheds have particularly high fish species richness or diversity. Of these, 56 percent are in the tropics, particularly Central Africa, mainland Southeast Asia, and South America.

Map 3: Endemic bird areas
(699 KB)
Birds can be good indicators of terrestrial biodiversity importance. For this analysis we used Endemic Bird Areas (EBA) developed by BirdLife International as an indicator of biological value.

Map 4: Aridity
(746 KB)
Arid lands are those in which rainfall is very limited and in which average humidity is low. One-third of the watersheds analyzed in this study lie to a significant degree in an arid zone.

Map 5: Population density
(751 KB)
Water availability for human use depends on how many people the available water supply must serve and how extensively water is used.

Map 6: Water availability
(753 KB)
Water experts define an area as potentially water stressed if the available annual supply is less than 1,700 cubic meters per capita and as potentially water scarce if the supply is less than 1,000 cubic meters per capita.

Map 7: Modified landscape (cropland and developed areas)
(704 KB)
About a third of the world's watersheds -- 34 basins of those analyzed -- have more than half their land area given over to agriculture or urban and industrial use.

Map 8: Cropland irrigation
(872 KB)
Because irrigation both affects the land and withdraws water from rivers or underground aquifers, the extent of irrigated cropland is also a useful indicator of watershed modification.

Map 9: Existing and proposed major dams
(713 KB)
There are 306 major dams in the world, most of them located in North America, Europe, and the Paraná river basin in South America. Dams fundamentally alter a watershed's hydrological and ecological characteristics.

Map 10: Remaining original forest cover
(705 KB)
Forests are crucial components of watersheds, maintaining water quality and moderating water flow. This analysis shows that 42 watersheds have lost more than 75 percent of their original forest cover.

Map 11: Extent of original forest cover lost
(702 KB)
The actual extent of forest lost is large; 9 basins have lost more than 500,000 square kilometers. The Yangtze and the Congo have lost more than 1 million square kilometers of original forest each.

Map 12: Area affected water erosion
(709 KB)
This indicator shows those bsins which have moderate to extreme levels of water-related soil erosion -- loss of top soil and terrain deformation.

Map 13: Urban population growth (1995-2000)
(792 KB)
Rapidly growing populations place heavy demands on freshwater resources. Because most population growth in coming decades will occur in urban areas, watersheds were ranked according to the population growth rate of major cities found within these basins.

Map 14: Tropical deforestation (1980-1990)
(812 KB)
Another indicator of vulnerability to future degradation is the rate of deforestation or conversion of forest land to other uses.

Map 15: Protected areas
(731 KB)
Protection of vulnerable portions of watersheds could be a potential countervailing measure to the growing pressures on watersheds. But more htan half -- 82 of the watersheds analyzed -- have less than 5 percent of their land area protected.

Watershed profiles (zipped)
(19,273 KB)
Full set of watershed profiles, in PDF format. Once downloaded, extract files then open the "index.html" file to navigate through the maps. To view individual profiles online, please go to "Maps."

Africa: Congo Watershed
(235 KB)

Africa: Congo Watershed: Kasal Subbasin
(127 KB)

Africa: Congo Watershed: Sangha Subbasin
(99 KB)

Africa: Congo Watershed: Lake Tanganyika Subbasin
(120 KB)

Africa: Congo Watershed: Ubangi Subbasin
(117 KB)

Africa: Lake Chad Watershed
(141 KB)

Africa: Lake Chad Watershed: Chari Subbasin
(113 KB)

Africa: Jubba Watershed
(147 KB)

Africa: Limpopo Watershed
(120 KB)

Africa: Mangoky Watershed
(81 KB)

Africa: Mania Watershed
(87 KB)

Africa: Niger Watershed
(204 KB)