Global Environment Outlook 3 (GEO 3)

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FRESHWATER

meet the needs of the growing population (World Water Council 2000a). The three major factors causing increasing water demand over the past century are population growth, industrial development and the expansion of irrigated agriculture. Agriculture accounted for most freshwater withdrawal in developing economies in the past two decades. Planners have always assumed that growing infrastructure. The damming of rivers has traditionally been one of the main ways to ensure adequate water resources for irrigation, hydropower generation and domestic use. About 60 per cent of the world’s largest 227 rivers have been strongly or moderately fragmented by dams, diversions or canals, with effects on freshwater ecosystems (WCD 2000). This infrastructure has provided important benefits in the form, for example, of increased food production and hydroelectricity. There have also been major costs. Over the past 50 years, dams have transformed the world’s rivers, displacing some 40-80 million people in different parts of the world (WCD 2000), and causing irreversible changes in many of the ecosystems closely associated with them. Emphasis on water supply, coupled with weak demand would be met by taming more of the hydrological cycle through building more enforcement of regulations, has limited the effectiveness of water resource management, particularly in developing regions. Policy-makers have now shifted from entirely supply solutions to demand management, highlighting the importance of using a combination of measures to ensure adequate supplies of water for different sectors. Measures include improving water use efficiency, pricing policies and privatization. There is also a new emphasis on integrated water resources management (IWRM), which takes into account all the different stakeholders in water resource planning, development and management (CSD 1997b). Irrigated agriculture Agriculture accounts for more than 70 per cent of freshwater drawn from lakes, rivers and underground sources. Most is used for irrigation which provides about 40 per cent of world food production (CSD 1997a). Over the past 30 years, the area of land under irrigation has increased from less than 200 million ha to more than 270 million ha (FAO 2001). During the same period, global water withdrawals rose from about 2 500 km 3 to

Major stocks of water

volume % of (1 000 km 3 ) total water total freshwater % of

Salt water Oceans

1 338 000

96.54

Saline/brackish groundwater

12 870

0.93

Salt water lakes

85

0.006

Inland waters Glaciers, permanent snow cover

24 064

1.74

68.7

Fresh groundwater

10 530

0.76

30.06

Ground ice, permafrost

300

0.022

0.86

Freshwater lakes

91

0.007

0.26

Soil moisture

16.5

0.001

0.05

Atmospheric water vapour

12.9

0.001

0.04

Marshes, wetlands*

11.5

0.001

0.03

Rivers

2.12

0.0002

0.006

Incorporated in biota*

1.12

0.0001

0.003

Total water

1 386 000

100

Total freshwater

35 029

100

Source: Shiklomanov 1993 Notes: totals may not add exactly due to rounding * Marshes, wetlands and water incorporated in biota are often mixed salt and freshwater

Precipitation, evaporation and run-off by region (km 3 /year)

35 000

evaporation run-off

32 200

30 000

28 400

14 100

25 000

22 300

12 200

4 600

20 000

18 300

15 000

8 180

16 200

10 000

8 290

18 100 17 700

7 080

2 970

2 510

10 100

5 000

2 310

5 320

4 570

0

Europe

South America

Asia

Australia/ Oceania

Africa

Antarctica

North America

Height of bars shows total precipitation; darker areas represent evaporation while lighter areas show run-off. Total annual precipitation on land is 119 000 km 3 , of which 72 000 km 3 evaporates, leaving some 47 000 km 3 of run-off Notes: regions do not correspond exactly to GEO regions; run-off includes flows to groundwater, inland basins, and ice flows of Antarctica Source: Shiklomanov 1993