Water for people.pdf - WHO Thailand Digital Repository

1 6 0 / C H A L L E N G E S T O L I F E A N D W E L L - B E I N GCities: Competing Needs in an Urban EnvironmentWith over 60 percent of the world’s population (nearly 5 billion people) expected to be living in urban areas by 2030(compared with less than 15 percent in 1990 and 48 percent in 2002), cities are rising to the top of the policy agenda.The Challenge of Water and CitiesOne of the most significant urban changes has been the growth ofcities to unprecedented sizes. The average size of the world’s 100largest cities grew from around 0.2 million in 1800 to 0.7 million in1900 to 6.2 million in 2000 (Satterthwaite, 2002). By 2000 therewere 388 cities with 1 million or more inhabitants (UN, 2002). Onlyin the late twentieth century did ‘megacities’ of 10 or more millioninhabitants develop, with sixteen cities becoming ‘megacities’ in2000, concentrating some 4 percent of the world’s population (seetable 7.2). Map 7.1 shows that the majority of these megacities liewithin regions experiencing mild to severe water stress. Meeting thewater needs of fast-growing cities can be extremely challenging.Map 7.1: Water stress in regions around megacitiesLos AngelesMexico CityNew YorkParisAlthough rapid urban change is often viewed as an uncontrolledflood of people, there is an economic logic underpinning global urbantrends. Most of the world’s urban population and most of its largestcities are concentrated in the world’s largest economies(Satterthwaite, 2002). In addition, the nations that urbanized mostquickly over the last forty years are generally the countries with thegreatest economic expansion (UN-Habitat, 1996). Table 7.1 highlightsthe fast urban growth in the less developed countries: while the mostdeveloped regions still have a much higher percentage of theirpopulation living in urban areas, the 2015 projection shows thebeginning of a reversing trend, with half of the population of the lessCairoKarachiNew DelhiBombayCalcuttaDhakaBeijingTokyoOsakaShanghaiRio de JanieroSao PauloBuenos Aires0 - 0.2 0.2 - 0.4 more than 0.4low water stress medium water stress severe water stressIn 2000, the majority of the sixteen megacities were found along the coasts, within regions experiencing mild to severe water stress; this is particularly true for the citieslocated on the Asian continent. ‘Water stress’ is a measure of the amount of pressure put on water resources and aquatic ecosystems by the users of these resources,including the various municipalities, industries, power plants and agricultural users that line the world’s rivers. The map uses a conventional measure of water stress, theratio of total annual water withdrawals divided by the estimated total water availability. This map is based on estimated water withdrawals for 1995, and water availabilityduring the ‘climate normal’ period (1961–1990).Sources: Map prepared for the World Water Assessment Programme (WWAP) by the Centre for Environmental Research, University of Kassel, 2002. For the water stress calculation: data from WaterGAPVersion 2.1.D; Cosgrove and Rijsberman, 2000; Raskin et al., 1997. For the megacities: UN, 2002.