Water for people.pdf - WHO Thailand Digital Repository

T H E N A T U R A L W A T E R C Y C L E / 7 9Table 4.3: Some large aquifers of the worldArea Volume ReplenishmentNo. Name (million km 2 ) (billion m 3 ) time (years) Continent1 Nubian Sandstone Aquifer System 2.0 75,000 75,000 Africa2 North Sahara Aquifer System 0.78 60,000 70,000 Africa3 High Plains Aquifer System 0.45 15,000 2,000 North America4 Guarani Aquifer System 1.2 30,000 3,000 South America5 North China Plain Aquifer Systems 0.14 5,000 300 Asia6 Great Artesian Basin 1.7 20,000 20,000 AustraliaThe largest aquifers occur in Africa, where they represent a very precious resource, since rainfall is almost non-existent. However, a wise exploitation of this resource is necessary.Sources: Margat, 1990a, 1990b.Map 4.3: Groundwater resources of the worldmajor groundwater basin with highly-productive aquifersarea with complex structure including some important aquifersarea with generally poor aquifers, locally overlain by river-bed aquiferspermanent icelarge freshwater lakeThe map clearly shows that the conditions of groundwater storage vary from area to area. While some regions are underlined by aquifers extending over large areas, othershave no groundwater, except for the floodplain alluvial deposits usually accompanying the largest rivers. In mountainous regions, groundwater generally occurs in complexesof jointed hard rocks.This global map is based on important hydrogeological mapping programmes that have been carried out on all continents except Antarctica. It forms thefirst step of a worldwide hydrogeological mapping and assessment programme (WHYMAP) recently started by UNESCO, IAH, the Commission for the Geological Map of theWorld (CGMW), the International Atomic Energy Agency (IAEA) and the German Federal Institute for Geosciences and Natural Resources (BGR). In this programme, a series ofgroundwater-related global maps will be produced and provided in digital format.Source: Map prepared for the World Water Assessment Programme (WWAP) by the Federal Institute for Geosciences and Natural Resources (BGR)/Commission for the Geological Map of the World(CGMW)/International Association of Hydrogeologists (IAH)/United Nations Educational, Scientific and Cultural Organization (UNESCO), 2002.