(6-B) ~ Regional Water Supplies and Use ~ Asia and Europe ~ [B1]~Asian Sub-continent ([B1a]~Bangladesh, [B1b]~India, [B1c]~Pakistan, [B1d]~Sri Lanka) [B2]~Far East, [B3]~Middle East, ([B3a]~Iran, [B3b]~Iraq, [B3c]~Israel, [B3d]~Jordan, [B3e]~Lebanon, [B3f]~Palestine, [B3g]~Saudi Arabia, [B3h]~Syria, [B3i]~Egypt, [B3j]~Turkey, [B3k]~Yemen, [B3l]~Qatar, [B3m]~Pakistan) ~ [B4]~Southeast Asia, [B5]~Europe, [B6]~Russia and Central Asian Republics, [B7]~Asia in General,
(6-C) ~ Regional Water Supplies and Use ~ Africa and Australia ~
(6-D) ~ Regional Water Supplies and Use ~ North and South America ~
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ir6
NOTE: The notation (su4) means that the adjacent data was used in the document analyzing the sustainability of the productivity of the world's systems for producing food, fiber and water.
SECTION (6-A) ~ Water Supplies ~ Global Overview ~ [A1]~Water Inventories, [A2]~Runoff, [A3]~Dam Construction, [A4]~Dam Inventories, [A5]~Water Use by Humans-Total, [A5a]~Non-Agricultural- and [A5b]~Agricultural, [A6]~Groundwater Supplies, [A7]~Desalinization, [A8]~Water Recycling, [A9]~Irrigation Water-Use Efficiency, [A10]~Surface Water Supplies, [A11]~Water Losses, ~
See Chapter 8 Section (8-E) (Databases) "World Resources 2005" for large compilations of:
~~ Actual Renewable Water Resources (km3 and m3/ person)
~~ Annual Water Withdrawals (km3 and m3/ person) (2000)
~~ Annual Water Withdrawals by Sector in 2000 (Agriculture, Industry, Domestic)
~~ Water Withdrawals (m3/ ha) in 2000
An overview of the Earth's water budget is contained in Ref. (80A1).
A global map plotting annual precipitation, minus evaporation, is in Ref. (92P1) (1977 UNESCO data).
A global map showing average precipitation (in mm./ year) is available from Paul Harrison and Fred Pearce, AAAS Atlas of Population and Environment, Victoria Dompka Markham, editor, 215 pages, AAAS and the University of California Press (2001).
A table of 16 principal rivers that provide desert water supplies is given on p.17 of Ref. (70P1) (names, locations, lengths, drainage areas, annual discharges, deserts, references).
Part [A1] ~ Global Overview ~ Water Inventories
One estimate of global water distribution:
|Water source||Water volume, cubic miles||Water volume|
|Percent of fresh water||Percent of total water|
|Oceans, Seas, & Bays|
|Ice caps, Glaciers,|
& Permanent Snow
|Ground Ice & Permafrost|
According to the United Nations, by 2020, water use is expected to increase by 40% to support the food requirements of a worldwide population that will grow from 6.7 billion people to 7.5 billion people. The U.N. estimate is that 1.8 billion people will be living in regions with extreme water scarcity. The US exported $115 billion of agricultural products in 2008 while importing $80 billion, according to the USDA. This is one of the few remaining businesses where the U.S. is a net exporter. (10Q1)
Total Renewable Freshwater Supply, by Country (Source: Pacific Institute) (10Q1)
|Country||Annual Renewable Water|
Resources (km3/ year)
According to the Pacific Institute for Studies on Development, Environment and Security, North Americans have access to over 6,000 m3/ person/ year stored in reservoirs. The poorest African countries have less than 700, and Ethiopia has less that 50 m3/ person/ year of water storage (09U1).
Global water markets (drinking water distribution, management, waste treatment, agriculture) are a nearly $500 billion market and growing rapidly (08C1).
Global freshwater consumption is nearly 4,000 km3/ year and is expected to increase by 25% by 2030 (2007 report by the Sustainable Asset Management group investment firm) (08C1).
The Intergovernmental Panel on Climate Change, a UN network of scientists, said in 2008 that, by 2050, up to 2 billion people worldwidecould be facing major water shortages (07S3).
The FAO said that two-thirds of the world's population could be threatened by water shortages by 2025. Today 1.2 billion people live in areas with insufficient water and an additional 0.5 billion could soon face shortages. Climate change and pollution are making it difficult for southern countries to provide themselves with food. Africa has 9% of the planet's water resources, but uses only 3.8%. Water resources on the African continent are not well-distributed. Lake Victoria, Africa's largest freshwater reserve, fell two meters below normal in 2005. ("Two-Thirds of World Population Could Face Water Shortage in 2025: FAO," Age, (3/22/07)). (su4)
Many rivers in irrigation-dependent regions of the world are already over-appropriated beyond the requirements of the aquatic ecosystems. Our assessment, following the assumptions earlier made by IWMI, suggests that irrigation might not contribute more than 270 km3/ year by 2015 (520 km3/ year by 2030, 725 by 2050). The remaining water requirements will have to be met in other ways (05F1).
See a listing of large databases in Chapter 8 Section (8-E) for sources of tabulations of:
~ Irrigated area irrigated with surface water (%), by country
~ Irrigated area irrigated with ground water (%), by country
~ Irrigated area irrigated with non-conventional sources (%), by country
~ Total population, rural population, urban population, by country
~ Agricultural water use (km3/ year and %), by country
~ Domestic water use (km3/ year and %), by country
~ Industrial water use (km3/ year), by country
~ Total water use (km3/ year), by country
~ Use of improved water sources (% of population) in 2002 (urban and rural) by country
~ Annual Renewable water resources (Total in km3) (per-capita in m3/ person) by country
~ Annual water withdrawals (Total in km3) (per-capita in m3/ person) by country
~ Annual water withdrawals by sector in 2000 (agriculture, industry, domestic) by country
~ Water withdrawals (m3/ha) in 2000, by country
Global precipitation rate: 110,000 km3/ year. About 2/3 of this precipitation is evaporated (transpired) into the atmosphere, leaving 40,000 km3/ year to flow to the sea via rivers, streams and underground aquifers ("groundwater"). Some 55 rivers in northern North America, Europe and Asia, with a combined flow of 5% of global runoff, are so remote that they have no dams on them. About 75% of the global runoff (i.e. 30,000 km3/ year) is in the form of floodwater. Large dams, which can hold 14% of the annual runoff, have increased the stable supply of water provided by underground aquifers and year-around river flow by nearly 1/3, bringing the total stable, renewable supply of freshwater to 14,600 km3. Of this total, 12,500 km3 is within reach, geographically and so is accessible for irrigation, industrial and household use (96P3). (su4.doc)
In developing countries, 90-95% of sewage and 70% of industrial wastes are dumped untreated into surface waters where they pollute usable water supplies (Ref. 15 of (02B2)).
In 2001, 2.3 billion people (about 38% of the world population) live in water basins that are at least stressed; 1.7 billion people live in water basins where scarcity conditions prevail. By 2025 these numbers will be 3.5 billion and 2.4 billion respectively (02B2).
In any given year, 54% of the available freshwater is used (01M1). Comment: How much is consumed? Answer is somewhere in this document. About 75% of water use is in irrigation.
Only 2.5% of all water on Earth is fresh water. Of that, 0.5% is accessible to people through ground water and surface water supplies (01M1).
Water evaporated from the ocean/ sea/ river surfaces takes about 10 days to fall again as rain (01P1) (90B2).
Some 160 km3 of water evaporates each day from the land surfaces of the Earth (58,440 km3 / year) (a 39 cm depth of water from the land if the removal were the same from each unit area of land) (01P1) (90B2).
About 0.001% of the Earth's total water resides in the atmosphere at any point in time - enough to deposit about 1 inch of rain if it fell uniformly throughout the world (01P1) (90B2).
Every 3100 years a volume of water equivalent to all the oceans passes through the atmosphere (01P1) (90B2).
For the 93 countries, irrigation water withdrawal is expected to grow by 14%, from the current 2128 km3/ year to 2420 km3/ year in 2030 (Table 4.10) (03B1). This increase is low compared to the 33% increase projected in harvested irrigated area, from 2.57 million km2 in 1997/1999 to 3.41 million km2 in 2030 (Table 4.8) (03B1) (Bruinsma, FAO).
In a survey of irrigation and water resources in the Near East region, it was estimated that the amount of water required to produce the net amount of food imported in the region in 1994 would be comparable to the total annual flow of the Nile River at Aswan (03B1).
The findings of the present study indicate that in developing countries, as in the past but even more so in the future, the mainstay of food production increases will be intensification of agriculture in the form of higher yields, more multiple cropping and reduced fallow periods (03B1).
The overall result for yields of all the crops covered in this study (aggregated with standard price weights) is roughly a halving of the average annual rate of growth over the projection period as compared to the historical period: 1.0%/ year during 1997/99 to 2030 against 2.1%/ year during 1961-99 (03B1).
Table 4.10 - Annual Renewable Water Resources (RWR) and Irrigation Water Requirements (03B1)
Column 1: Sub-Saharan Africa ~ ~ ~ | Col. 4: South Asia
Col. 2: Latin America/ Caribbean ~ | Col. 5: East Asia
Col. 3: Near East/ North Africa~ ~ | Col. 6: All developing countries
Column - - - - - - - - - - - | ~1 | ~2~ | 3 | 4~ | 5~ | 6 .Precipitation (mm)-~ ~ ~ ~ ~ | 880| 1534|181|1093|1252| 1043
Internal RWR (km3)-~ ~ ~ ~ ~ |3450|13409|484|1862|8609|28477
Net incoming flows (km3)-~ ~ | ~ 0| ~ ~0| 57| 607| ~ 0| ~ ~0
Total RWR (km3)- ~ ~ ~ ~ ~ ~ |3450|13409|541|2469|8609|28477
Irrigation water withdrawal
Irrigation efficiency (1998)%| ~33| ~ 25| 40| ~44| ~33| ~ 38
Irrig.water withdrawal(1998)*| ~80| ~182|287| 895| 684| 2128
- ~idem as a % of RWR~ ~ ~ ~ | ~ 2| ~ ~1| 53| ~36| ~ 8| ~ ~7
Irrigation efficiency (2030)%| ~37| ~ 25| 53| ~49| ~34| ~ 42
Irrig.water withdrawal(2030)*| 115| ~241|315|1021| 728| 2420- ~idem as a % of RWR~ ~ ~ ~ | ~ 3| ~ ~2| 58| ~41| ~ 8| ~ ~8
Note: RWR for all developing countries exclude regional net incoming flows to avoid double counting.
"Irrigation efficiency" is defined as the fraction of irrigation water actually consumed by crops.
China, India, Saudi Arabia, North Africa, and the US over-pump and deplete aquifers at 160 billion cubic meters annually. Since it takes it takes 1,000 tons of water to produce 1 ton of grain, this 160-billion-ton water deficit is equal to 160 million tons of grain, or 50% of the US grain harvest. Some 480 million of the world's 6 billion people are being fed with grain produced with non-sustainable use of water. About 70% of the water consumed worldwide is used for irrigation; 20% by industry, and 10% for residential purposes. The rural-to-urban migration occurring throughout most of the developing world means that residential use of water triples due to indoor plumbing. (See the document on the informal economy elsewhere in this website.) If we stabilized water tables everywhere by simply pumping less water, the world grain harvest would fall by 160 million tons, or by 8% (World Watch (6/21/00)). (su4)
Population pressures under 600 persons/ flow-unit (P/FU; 1 FU=1 million cubic meters) are not considered a serious issue, although water quality problems and dry season supply problems may occur. Between 600-1000 P/FU, chances of more recurrent quantitative or/ and qualitative supply problems increase notably: this is called the "water stress" stage. Between 1000-2000 P/FU such problems are common and affect human and economic development; this is the "scarcity" stage. 2000 P/FU is seen as the maximum population pressure that can be handled in the present state of technology and management capabilities; it has been labeled "water barrier". This scale was developed from the observation of areas where both per-capita supplies and resource use problems were well documented (96M2).
Total volume of fresh water on land and in air: 8.5 million km3. 8.3 million km3 are ground water, 0.126 million km3 occur in lakes, rivers and streams. The balance (0.074 million km3) is atmospheric vapor, soil moisture and seepage (80C2) (Water Resources of the World data). Comments: This breakdown appears to neglect freshwater in glaciers and ice caps, e.g. Greenland.
Global Water Resource Summary (03W1) (UNESCO; Internationally Shared Aquifer Resources Management)
Oceans ~ ~ ~ ~ | 96.50%
Fresh water~ ~ | ~2.53%
Brackish water | ~0.97%Total Water~ ~ |100.00%
Global Fresh Water Resource Summary (03W1) (UNESCO: Internationally Shared Aquifer Resources Management)
Glaciers/ permanent snow | 69.600%
Ground water ~ ~ ~ ~ ~ ~ | 30.100%
Lakes, marshes, swamps ~ | ~0.290%
Soil Moisture~ ~ ~ ~ ~ ~ | ~0.050%
Atmosphere ~ ~ ~ ~ ~ ~ ~ | ~0.040%
Rivers ~ ~ ~ ~ ~ ~ ~ ~ ~ | ~0.006%
Living Organisms ~ ~ ~ ~ | ~0.003%Total Fresh Water~ ~ ~ ~ |100.089%
Of the world's water supply, 97.5% is salt water. Most of the remaining 2.5%, fresh water, is in glaciers and ice caps, unavailable for use by living things. 0.77% is in lakes, rivers, swamps, and aquifers, or in the atmosphere, or in soils and plant tissues (98S3).
Only 2.5% of the world's water is not saline. Of that, 2/3 is locked up in ice-caps and glaciers. 20% of what is left is in remote areas and virtually all of the rest - monsoons, storms and floods - comes at the wrong time and place. (Agence France Presse "Major Water Crisis Looms", 3/13/00) (World Commission on Water for the 21st century data).
About 20% of the water running to the sea (presumably via either surface water runoff or via aquifers) is too remote to supply any cities or farming regions. About 50% runs off to the sea in the form of floods. Much of the remainder occurs in regions where abundant rainfall makes irrigation unnecessary (96P2).
Average recycling time for ground water: 1400 years (00S1).
Average recycling time for river water: 20 days (00S1).
About 97% of the planet's liquid freshwater is in aquifers (00S1). Comments: Does this include glaciers and ice-caps? No, it says "liquid".
Present storage capacity of large dams: 5,500 km3, of which 3,500 are actively used in regulation of run-off (96P2). (See the soil degradation review for much more data on dams.) Comments: In the soil degradation review it talks about a capacity of the world's dams being 6000 km3 or more, but this figure could include both large and small dams.
Renewable Fresh Water Resources (1998) (in units of 1000 cubic yards/ capita/ year) (Wall Street Journal (6/3/99)) (WRI data) (98B3)
Canada ~ |122.7
Brazil ~ | 40.8
Russia ~ | 37.8
US ~ ~ ~ | 11.7
China~ ~ | ~2.9
Comments: Canada is said to have 20% of the world's fresh water, but Canadian officials contend that, if glaciers and polar ice caps are ignored, Canada has only 9% of the world's renewable fresh water resources. British Columbia and Alberta have banned exports of bulk fresh water, and the Canadian government is planning to (Wall Street Journal, 2/11/99).
"Global Water Outlook to 2025: Averting an Impending Crisis" presents three alternative future scenarios for global water supply and demand, and food production and consumption, based on the results of the IMPACT computer model. Only one of the 3 scenarios is given below (02I1).
BUSINESS-AS-USUAL SCENARIO Projections:
By 2025, water scarcity will cause annual global losses of 350 million metric tons of food production - slightly more than the entire current US grain crop.
Consumption of water for all non-irrigation uses will rise by 62%.
Household water use will increase by 71%, of which more than 90% will be in developing countries.
By 2025 industrial water demand in the developing world will exceed the demand in developed countries.
Water scarcity will cause substantial shifts in where the world's food is grown. Developing countries will dramatically increase their reliance on food imports. In sub-Saharan Africa, grain imports will more than triple. Poor countries, unable to finance imports, will experience increased hunger and malnutrition.
Water scarcity is defined as less than 1000 m3 of water available/ person/ year, while water stress means less than 1500 m3 of water is available/ person/ year (99S1).
In the last 50 years, global demand for water has tripled with the rapid worldwide spread of powerful diesel and electrically driven pumps that can pump ground water (02E1).
When the Soviets decided, after a poor harvest in 1972, to import grain rather than tighten their belts, world wheat prices climbed from $1.90/ bushel in 1972 to $4.89 in 1974 (02B1). Comments: The point here is that 1 ton of wheat requires 1000 tons of water and 1 ton of wheat is more transportable than 1000 tons of water. So water shortages translate readily into wheat shortages and the demand elasticity of wheat is very low. (See below.)
Some 70% of world water use, including all the water diverted from rivers and pumped from underground (aquifers), is used for irrigation. Thus if the world is facing a water shortage, it is also facing a food shortage. Water deficits, which are already spurring heavy grain imports in numerous smaller countries, may soon do the same in larger countries, such as China or India. Even with over-pumping of its aquifers, China is developing a grain deficit. (Comments: But it is not yet (2002) a net importer.) After rising to an historical peak of 392 million tons in 1998, grain production in China fell below 350 million tons in 2000, 2001, and 2002. The resulting annual deficits of 40 million tons or so have been filled by drawing down China's grain reserves. But if this continues, China will be forced to turn to the world grain market (02B1).
Scores of countries are running up regional water deficits, including nearly all of those in Central Asia, the Middle East, and North Africa, plus India, Pakistan, and the US. Historically, water shortages were local, but shortfalls can cross national boundaries via the international grain trade. Water-scarce countries often satisfy growing needs of cities and industry by diverting water from irrigation and importing grain to offset resulting loss of production. Since a ton of grain equals (requires) 1000 tons of water, importing grain is the most efficient way to import water (02B1).
The assessment in an unclassified CIA report called "Global Trends 2015," makes a number of predictions about the global political landscape. In terms of global resources, the report concludes that by 2015, nearly half of the world's population - more than 3 billion people - will be in countries lacking sufficient water. The 70-page report is one result of an unusual 15-month collaboration between the National Intelligence Council, a sort of analytical think tank of senior intelligence officials that works alongside the CIA, and dozens of outside scientific, diplomatic and corporate experts (00U1) (00C1).
In 2015 nearly 3 billion out of the estimated global population of 7.5 billion people will find it difficult or impossible to find water for food, industry and personal needs. Today's trouble zones are Afghanistan, Pakistan, India, China, Iran, Israel, Jordan, and Syria. According to John Gannon, a former assistant director of the CIA and former chairman of the National Intelligence Council, water scarcity now constitutes "a significant issue in security" as water shortages "encourage refugee movements which, if they spill over into other countries, can engage us." "If people don't have water, they can't live. They are going to move or they are going to die." According to the CIA report "Global Trends 2015" none of the proposed solutions - importing water, water conservation, expanded use of desalinization of seawater, or developing genetically modified crops that use less water or more saline water - will be sufficient to substantially change the outlook for water shortages in 2015 ("Water Shortages Could Be New Cause of Conflicts", Scripps Howard News Service, 12/12/01) (00C1).
Part [A2] ~ Global Overview ~ Water Supplies ~ Runoff ~
Canalization (channelization?) of rivers and other natural water bodies was responsible for more than 100,000 deaths (worldwide) during the 1990s, due to floods that caused $243 billion in damage (05F3).
Global Runoff and Population, by Continent, 1995 (96P3).
Region- - - - - - -|Runoff~ |Share of| Share of
- - - - - - - - - -|km3/year|Runoff~ |PopulationEurope ~ ~ ~ ~ ~ ~ | 3240 ~ | ~8%~ ~ | 13%
Asia ~ ~ ~ ~ ~ ~ ~ |14550 ~ | 36 ~ ~ | 60
Africa ~ ~ ~ ~ ~ ~ | 4320 ~ | 11 ~ ~ | 13
North & C. America | 6200 ~ | 15 ~ ~ | ~8
South America~ ~ ~ |10420 ~ | 26 ~ ~ | ~6
Australia, Oceania | 1970 ~ | ~5 ~ ~ | <1Totals ~ ~ ~ ~ ~ ~ |40700 ~ |101 ~ ~ |100
Global runoff estimates range from 33,500-47,000 km3/ year. The estimate of L'Vovich et al (Ref. 6 of (96P2)) (40,700 km3/ year) is in the middle of the range (96P2). Comments: More details on this are in the review of soils degradation.
Average runoff worldwide: 39,500-42,700 km3/ year ((99F1), p. 31) ((97S1), p. 13). Most of this runoff occurs in flood events or is otherwise not accessible to human use. Only 9000 km3/ year is readily accessible to humans, and an added 3500 km3 is stored in reservoirs ((97W1), p. 7). Comments: The reservoir storage datum may be obsolete. More recent figures are in the vicinity of 6000 km3 (See Soil Degradation Review).
Evaporation lifts 500,000 km3/ year of water into the atmosphere - 86% from oceans, 14% from land (92P1).
Continents lose water at 70,000 km3/ year from evaporation, but gain 110,000 km3/ year through precipitation. The net, 40,000 km3/ year = 7400 m3/ person (92P1). About 2/3 of this 40,000 km3 runoff in the form of floods, leaving 14,000 km3/ year of stable surface water supply (92P1).
Rivers that no longer reach the sea for at least parts of the year (99P1)
Yellow ~ ~ | (China - see elsewhere in this review document)
Ganges ~ ~ | (Asian sub-continent)
Indus~ ~ ~ | (Asian sub-continent)
Nile ~ ~ ~ | (Northeast Africa)
Amu Darya~ | (Central Asia)
Syr Darya~ | (Central Asia)
Chao Phraya| (Thailand)
Colorado ~ | (Southwestern North America)
Rio Grande | (Southern US) (From another reference - see elsewhere.)
The inaccessible remote flows of the Amazon (95% of total flow = 5387), Zaire-Congo (50% of total flow = 662) and northern tier undeveloped rivers (95% of total flow = 1725) amounts to 7,774 km3/ year (19% of total annual run-off). This leaves 40,700-7,774 = 32,900 km3/ year of accessible river flow (96P2). About 11,100 km3/ year of global run-of (27% of total) is renewable groundwater and base river-flow (Ref. 6 of (96P2)). So 0.27x 7,774 = 2100 km3/ year is renewable groundwater and base river flow in inaccessible remote areas (96P2).
Arid and semi-arid zones of the world receive 2% of the world's runoff, even though they occupy 40% of the terrestrial area ((97W1), p. 7). Comments: Transpiration losses are a large fraction of rainfall in arid and semi-arid regions.
For 82% of the world' agro-ecosystems, rainfall is the sole source of water for agricultural production ((00W1), p. 66).
Some 40% of developing-world farmers depend upon regular flows of rivers and streams to irrigate their croplands (96M1).
Part [A3] ~ Water Supplies ~ Dam Construction
Since 1950, the number of large dams (those over 15 meters high) has increased from 5,000 to 45,000 worldwide. Reservoirs increase evaporation. The annual loss of water from a reservoir in arid or semiarid regions, where evaporation rates are high, is typically equal to 10% of its storage capacity. The Colorado River now rarely makes it to the sea. With the states of Colorado, Utah, Arizona, Nevada, and, most important, California depending heavily on the Colorado's water, the river is simply drained dry before it reaches the Gulf of California (07B1).
In Southeast Asia the flow of the Mekong River is being reduced by the dams being built on its upper reaches by the Chinese. The downstream countries, including Cambodia, Laos, Thailand, and Viet Nam (168 million people) complain about the reduced flow of the Mekong, but this has done little to curb China's efforts. The same problem exists with the Tigris and Euphrates Rivers, which originate in Turkey and flow through Syria and Iraq en route to the Persian Gulf. This river system is being over-used. Large dams erected in Turkey and Iraq have reduced water flow to the once "fertile crescent," helping to destroy more than 90% of the formerly vast wetlands that enriched the delta region (07B1).
Of the 980 large dams in sub-Saharan Africa, 589 are in South Africa, whereas Tanzania only has two large dams ("Water Stress in Sub-Saharan Africa," Council on Foreign Relations, 8/7/06.).
From the 1950s to the mid-1970s, about 1000 large dams came on line annually. By the early 1990s, about 260 large dams were being completed annually (99P1).
Construction begins on 170 dams/ year around the world (92P1). Comments: Probably refers to large dams, not all dams.
Only one of Japan's 109 major rivers remains non-dammed (Ref. 2 of (92P1)).
An average of 360 dams/ year were built in the world between 1951-1974 (Ref. 4 of (92P1)) (93P2).
The number of dams under construction in 1993 rose 9% to 1240 after a much smaller increase in 1992. In the 1980s, dam construction worldwide averaged less than half of the preceding 25 years (95G2).
The World Bank was involved with an average of 18 dam projects/ year during 1980-1985, and 6/ year during 1986-1993 (95G2).
Construction of dams higher than 100 meters rose 27% during 1991-1993. Half of these structures were built in Japan, China and Turkey (95G2).
A USGS study notes that new dam construction might increase that supply by 0.33%/ year over the next 30 years, but population is expected to grow at four times that rate (98S3). Comments: It is not clear whether the USGS study accounts for the rate of filling of dam backwater storage volume with sediments - 0.5-1.0%/ year. The term "supply" might refer to storage capacity - but then again it might not.
Leading Builders of Big Dams (higher than 10 meters) (95G2)
Col. 2 - 1993 Dam starts: Col. 3 - Dams Under Construction
Country|Col.|Col.| Country |Col.|Col.
- - - -| 2~ | 3~ | - - - - | 2~ | 3China~ | 85 |311 | Italy ~ | 0~ | 37
Turkey | 84 |190 | Tunisia |16~ | 28
Japan~ | 11 |140 | Algeria | 6~ | 27
S.Korea| ~2 |125 | Iran~ ~ | 1~ | 76
India~ | 48 | 76 | Thailand| 7~ | 17
USA~ ~ | 30 | 55 | Greece~ | 3~ | 14
Spain~ | 16 | 53 | France~ | 8~ | 12
Romania| ~0 | 39 | Brazil~ | 4~ | 12
Comments: Total dam starts are about 1% of large-dam inventory.
Part [A4] ~ Water Supplies ~ Dam Inventory ~
More than 85% of the large dams now standing have been built during the past 35 years (96P3).
Nearly 1000 large dams were constructed every year from the 1950s through the mid-1970s. The number dropped to about 260 during the early 1990s (96P3).
Australia's Dam Storage Capacity in 1990 (in km3) (01P1):
Australian Capital Territory 0.125 / South Australia 0.267 / Northern Territory 0.275 / Western Australia 7.011 / Queensland 9.459 / Victoria 12.226 / Tasmania 24.167 / New South Wales 25.389 / (Total = 78.919).
Of the world's 45,000 large dams, 22,104 are in China; 6,390 are in the US and just over 4,000 in India. China is planning a series of giant dam cascades across rivers such as the Mekong, the Salween and the Bramaputra that are vital to the prosperity of Southeast Asia. If as a result these rivers end up disappearing like the Yellow, the Huai or the Hai in China, the consequences will be incalculable. ... Hydropower enthusiasts say that if China does not keep building dams at a furious rate, tripling capacity from 60 giga-watts to 171 gigawatts by 2020, it will be forced to burn more coal, with dire consequences for the world's atmosphere." (Continued below)
** "China now ranks second globally to the US in installed electricity capacity (338 giga-watts in 2000) but its use of electricity is just 38% of the world's average. If, by 2050, its population peaks at 1.6 billion and per-capita energy use reaches the world average, it will be adding the generating capacity of Canada every four years. China currently burns more than a billion tonnes of coal a year to produce 75% of its energy. Even the most optimistic assumptions foresee coal consumption growing by about 5%/ year. China has unveiled ambitious plans to cut its reliance on coal to about 55% of its energy needs. By 2030 coal is expected to provide 62%, oil 18%, natural gas 8%, hydropower 9%, and nuclear power 3% of China's energy consumption. By 2050, Chinese planners believe coal consumption should be down to 35% of consumption, with oil and natural gas accounting for 40-50% and primary energy sources such as nuclear, hydro, solar and wind power accounting for 15-20%. ... By 2030 oil is scheduled to supply 18% of China's needs - making it as important a consumer of Middle Eastern oil as Japan or the US." (China: Collision between population and the environment, Asia Times (8/23/03)
There were 5000 large dams (more than 15 meters high) worldwide in 1950. There are now 45,000 (02U3).
Some 40,000 large dams (over 15 meters high) now exist in the world, vs. 5000 in 1950. Small dams number about 800,000 (99P1).
Collectively, dams worldwide have a storage capacity of 6,600 km3 ~ 20% of annual volume of floodwater heading for the sea (99P1).
Present storage capacity of large dams: 5,500 km3, of which 3,500 are actively used in regulation of run-off (96P2). So accessible run-off = 11,100 -2,100 + 3,500 = 12,500 km3/ year (96P2).
Worldwide, reservoirs are estimated to be losing storage capacity at 1%/ year (i.e. 66 km3/ year). Replacing this lost storage by building new reservoirs could cost $10-$13 billion/ year, assuming enough new reservoir sites could be found. If sediments had to be dredged out of existing reservoirs, the cost would climb to $130-$200 billion/ year. (K. Mahmood, "Reservoir Sedimentation: Impact, Extent and Mitigation", World Bank, Washington DC, 1987). Comments: These statements are also in the Soil Degradation Review.
Part [A5] ~ Water Supplies ~ Water Use by Humans ~ Total ~
Table 1. Water Import Dependence in Selected Countries during 1997-2001.
Source: Chapagain and Hoekstra, Water International, March 2008.
Between 1900 and 1995, global freshwater consumption rose six-fold. This was more than twice the rate of population growth (09H1).
Globally, demand for freshwater increases by 64 billion m3 per year (UNESCO data) (09H1).
Over the past 50 years, as the world's population rose from 3 billion to 6.5 billion, water use increased by a factor of 4 (09U2).
The facts are that over a billion people don't have access to save drinking water results in 2-4 million deaths annually (WHO (2005) cited in Ref. ((06O1) page 3)
Some 1.1 billion people do not have reliable access to potable drinking water, and 3-4 million die each year of waterborne diseases (05F3).
Global demand for water is growing by 64 billion m3 (2.2 trillion cubic feet) per year (09I1).
In the past 50 years extraction of water from rivers, lakes and aquifers has tripled. Agriculture accounts for 70% of water withdrawals (more than 90% in some developing countries) (09I1).
The U.N. says that, since 1990, 1.6 billion people have gained access to safe drinking water. But nearly a billion people still lack safe drinking water (09U1).
Water Resources and Withdrawals (09U2)
Withdrawals per person are in units of cubic meters/ person.
Source: UN World Water Development Report
The world's demand for water has tripled over the last half-century (07B1).
The world's demand for hydroelectric power has more than tripled over the last half-century. As a result, dams and diversions of river water have drained many rivers dry. As water tables fall, the springs that feed rivers go dry, reducing river flows even more (07B1).
Over the next two decades, global use of water is expected to increase by over 40% (07B1).
Over the next two decades, global water use is projected to increase by 40%. In 1999 the UN reported that 200 scientists in 50 countries had identified water shortage as one of the two most worrying problems for the new millennium ("Dawn of a Thirsty Century," BBC News (6/14/08)).
More than one billion people in developing nations lack access to safe drinking water. More than 2 billion people in developing nations lack proper sanitation (08E2).
Global water demand for food production might easily double by 2030 (08E2).
By 2050, feeding the world's population may require some 12,000 km3 of water (08E2).
Globally, more than 1 billion people don't have safe drinking water and 2.6 billion don't have access to sanitation. Between 2 and 5 million people die each year from water-related diseases ("Worldwide-water Scarcity, Contamination a Threat," Standard (3/22/05).).
Some 77% of China's effluent is untreated, 70% (of Chinese?) have no access to safe drinking water, and 400 of 600 Chinese cities face water shortages. Contamination and lack of capacity are the leading factors for water shortage. China's market for water and wastewater treatment will increase to $22.7 billion in 2005 from $18.7 billion in 2004 and is expected to reach $33.2 billion by 2010 ("Worldwide-water Scarcity, Contamination a Threat," Standard (3/22/05)).
Water is one of the two key raw materials in photosynthesis, the other being carbon dioxide. When leaves open to take in CO2, huge amounts of water evaporates, in most climates of the order of 1500 m3/ ton biomass produced, but in poverty stricken dry climate countries often twice this amount due to large losses and low water productivity. To produce a balanced diet of 3000 kcal/ person/ day (20% animal protein) involves a consumptive water use of 1300 m3/ person/ day. This water is being picked up by the roots from the so-called green water in the soil consisting of infiltrated rainfall. Water may be added to the soil by irrigation with water withdrawn from the blue water available in rivers and aquifers. This water requirement is 70 times larger than the amount often assumed as the basic need for household supply (50 liters/ person/ day) (05F1).
The Swedish assessment (05F1) suggests that to reach the MDG 2015 Target, an additional consumptive water use of 2200 km3/ year (globally) will be required. This corresponds to a 50% increase from today's global consumptive use of water. If covered by irrigation only, it would involve more than a doubling of all the water withdrawals from rivers and aquifers today, and would be absolutely unacceptable in view of the damage already caused by irrigation in terms of depleted rivers and degraded aquatic ecosystems. Looking beyond 2015 and accepting the FAO-projected average diet in the developing countries for 2030 of 3000 kcal/ person/ day, an additional consumptive water use of 4200 km3/ year would be required by 2030 assuming that hunger be altogether eradicated, increasing to an additional 5200 km3/ year by 2050 in order to feed also the additional population (05F1).
Global freshwater use tripled during the second half of the 20th century as population more than doubled and as technological advances enable farmers and other water users to pump groundwater from greater depths and to harness river water with more and larger dams. As global demand for water soars, pressures on the world's water resources are straining aquatic systems worldwide. Rivers are running dry, lakes are disappearing, and water tables are dropping. Pressure on water resources is particularly acute in arid regions that support agricultural production or large populations-regions where water use is high relative to water availability. The Middle East, Central Asia, North Africa, South Asia, China, Australia, the western US, and Mexico are especially prone to water shortages (06M1).
It is generally believed that per-capita water availability should be 1700 m3 (about 60,000 ft.3) per year. In India, utilizable water is 1000 m3/ year and may slip to 800 m3 by 2050 when India's population is expected to be 1.6 billion (06M2).
Even though more than 2.4 billion people got access to safe drinking water for the first time during the past 20 years, an estimated 1.7 billion people still lack it. Perhaps 2.6 billion people in the world lack basic sanitation. Two million tons of human waste is released into rivers and streams around the world annually. About 1.8 million people, mostly young children, die from diarrhea and related diseases every year. Many of those deaths could be prevented with clean water and sanitation (05W1).
Diets based on meat from grain-fed cattle can deplete as much as 5000 liters per capita per day, while vegetarian diets deplete less than half that much water (00R1).
Rockström et al (1999) (99R2) estimated that the amount of water consumed by agriculture would have to increase from 6100 km3 to 9700 km3, given current trends in population growth, improvements in living standards and water use patterns.
Meeting just the food needs of an additional 2.6 billion people expected by 2025 would require an additional 1040 km3/ year of water (96P3).
Estimated Global water Demand and Consumption, by Sector, around 1990 (96P3)
The Western US population is 86% urban (01M1).
The rate of population growth in the Western US is 32% in the past 25 years (vs. 19% for the US as a whole) (Pamela J. Case and Gregory S. Alward, Patterns of Demographic, Economic and Value Changes in the Western US: Implications for Water Use and Management, The Western Water policy Review Advisory Commission, Springfield Virginia (1997) p. 7).
Water consumption data (01P1) (m3/ person/ year)
U.S.~ ~ ~ |1100
Israel~ ~ | 100
Egypt ~ ~ | 50-60
Jordan~ ~ | 40-60
Syria ~ ~ | 40-60
Lebanon ~ | 40
Gaza strip| 20
Some 36% of Africa's population lacks safe drinking water and by 2025, one in two Africans will be living with water stress or water scarcity. (Water stress describes a country in which each person has less than 1500 m3/year.) Only 6% of Africa's farmland is irrigated ("Sustainability: Do 'Water Wars' Still Loom in Africa?" InterPress Service (5/15/04)).
The UN said the availability of clean fresh water would be critical for the future because of the escalating population in the world, especially in third world countries. There are up to two billion people without access to safe drinking water and 2.4 billion lack sanitation. More than three million people die every year from unsafe water. Approximately $30 billion/ year is spent on meeting drinking water and sanitation requirements worldwide. An added $14-$30 billion/ year would be needed to meet the targets on water and sanitation ("UN Says World Might Face Immense Water Problem," Business World (Philippines) (10/31/03).)
Globally, water use has roughly tripled during 1950-1990 and is now 4430 km3 - 35% of the accessible supply. At least an additional 20% is used in-stream to dilute pollution, sustain fisheries and transport goods. So humans actually use more than 50% of the accessible water supply (96P3). Comments: The differentiation between "use" and "consumption" is far from clear in this analysis. When water flows through an urban setting (in via water supply pipes, out via sewer pipes) it picks up salt. Going through two urban settings loads the water with enough salt to start to reduce its value as irrigation value. (See details elsewhere in this review document.) It is not clear whether this fact has been taken into account in the above analysis.
Humanity now uses 26% of total terrestrial evapo-transpiration and 54% of runoff that is geographically and temporally accessible (96P2).
One recent study concluded that over 50% of all accessible water was diverted for human use in the mid-1990s (98S3).
Percent of the world's population with improved water supply rose from 79% to 82% in 2000 (03U1).
Some 67% of the world's population will face water shortages by 2025 ("Running on Empty," a Christian relief and development agency Tearfund, based in the UK) (Environment News Service (3/22/01)).
(Supply/ Demand) Most of the 3 billion people projected to be added worldwide by 2050 will be born in countries already experiencing water shortages (02B1).
Worldwide, 41,000 children/ day die because of unsafe water (03U1).
(Water Quality Constraints) 17% of the world's population has no access to safe drinking water (03U1).
(Water Use Trends) Global water use tripled between 1950 and around 2000 (03U1).
(Water Use Trends) Global water consumption rose six-fold from 1900-1995. This is more than twice the rate of population growth (Environment News Service (3/22/01)).
(Water Use Trends) Water withdrawals from rivers and underground reserves have grown by 2.5-3%/ year since 1940, significantly ahead of global population growth (01U1).
Estimated global water use and consumption (km3/ year) (96P2)
Sector - - - - - - -| Use |ConsumptionAgriculture ~ ~ ~ ~ |2880 |1870 (81.8%)
Industry~ ~ ~ ~ ~ ~ | 975 | ~90 ( 3.9%)
Municipalities~ ~ ~ | 300 | ~50 ( 2.2%)
Reservoir losses~ ~ | 275 | 275 (12.0%)
In-stream flow needs|2350 | ~ 0 ( 0.0%)Totals~ ~ ~ ~ ~ ~ ~ |6780 |2285(100.0%) *
* 18% of 12,500 available runoff
Comments: Reservoir evaporation losses should be apportioned among the other water-consumption categories, suggesting that agriculture accounts for about 93% of water consumption by humans.
(Water Use Trends) Humans withdraw about 4000 km3 of water annually - about 20% of the normal flow of the world's rivers (their non-flood or "base flow") (97S1).
(Water Use Trends) Between 1950 and the mid-1990s, global water use more than tripled (97P3).
Global water uses (municipal, industrial and agricultural) are plotted vs. time (1900-2000) in Fig. 3 of Ref. (96A1).
A plot of global water use (km3/ year) vs. time (1900-1992) is in Ref. (92P1).
Per-capita water consumption is rising twice as fast as the world's population (98S1).
One billion people lack access to safe water, and 2 billion lack proper sanitation. By 2020, water use by humans is expected to increase by about 40%, and 17% more water than is available now will be needed to grow the necessary food. (Agence France Presse "Major Water Crisis Looms" (3/13/00)) (World Commission on Water for the 21st Century data).
(Supply/ Demand) At least 400 million people live in regions with severe water shortages. By 2050, it will be 4 billion (98S1).
(Supply/ Demand) Hydrologist Malin Falkenmark of Sweden, have calculated that in 1990, 28 countries containing 335 million people faced chronic water stress or outright scarcity. By 2025, water shortages may plague up to 52 countries, affecting as many as 3.2 billion people; roughly 40% of the projected global population (98H1).
By 2050, nearly half of the world will have insufficient water. As much as 42% could be facing either water stress (having less than 1700 m3/ year/ person) or scarcity (less than 1000 m3/ year/ person) (98S1).
Parameter - - - - |1995 | 2050
World population# | 5.7 | 9.4
Water Sufficiency | 92% | 58%
Water Stress~ ~ ~ | 5%~ | 24%
Water Scarcity~ ~ | 3%~ | 18%
World water-use is plotted vs. time (1900-93) and broken down by sector (agriculture, industry, municipal, reservoir losses) in Ref. (93P2).
Global water use has tripled since 1950, and is now 4340 km3/ year (92P1) (95P2).
Water Deficits in Key Countries and Regions, Mid-1990s (km3/ year) (99P1)
Region - - -|DeficitIndia ~ ~ ~ |104.0
China ~ ~ ~ | 30.0
US~ ~ ~ ~ ~ | 13.6
N. Africa ~ | 10.0
Saudi Arabia| ~6.0
Other ~ ~ ~ |(40 )(?)Global Total|200.
Number (millions) of People in Countries with less than 1700 m3/ capita/ year runoff (99P1)
Region - - |1995|2025(projection)Africa ~ ~ |295 | 908
Asia ~ ~ ~ | 86 |1957
Middle East| 86 | 185Totals ~ ~ |467 |3050
(Supply/ Demand) 26 nations suffer water scarcity to the extent of limiting food production, economic development, sanitation and environmental protection. The number of such nations is expected to reach 35 (of about 158) by 2020 (Ref. 29 of (96G1)).
(Global Water Use Trends) Human water consumption doubled during 1940-1980, and 1980-2000 will probably see another doubling (93G1).
(Global per-capita water-use): 800 m3/ year - 50% higher than in 1950 and, in most parts of the world, continues to climb (Ref. 1 of (93P2)). Comments: What percent of this is consumptive use?
Two billion people worldwide suffer chronic water shortages (93G1).
Ref. (93G1) contains 217 tables of data on water resources at the global-, regional- and national levels; consumption patterns and trends; water-related diseases and sanitation; pollution, irrigation agriculture, and water laws, policies and politics (93G1).
(Per-Capita Water Use) One estimate of the water requirements for drinking, sanitation, commerce and industry at the Israeli standard of living is 75-150 m3/ person/ year (not counting needs for agriculture) (94G1). Comments: What percent of this is consumptive use?
A country is considered to face water stress when annual water supplies (runoff?) drop below 1700 m3/ person/ year, and faces water scarcity when water supplies are less than 1,000 m3/ person/ year. Today, 31 countries face water stress or water scarcity. By 2025 population growth alone is expected to add another 17 countries to the list. Water shortages would then affect 2.8 billion people, or 35% of the world's projected population compared with 8% today. (Gardner-Outlaw, T. and Engleman, R. "Sustaining water, Eating scarcity: A second update", Washington DC, Population Action International, 1997. pp. 2-19).
Many hydrologists believe that 500 m3/ person/ year is the minimum water supply needed to avoid limiting the options available to a society (Ref. 27 of (94G1)). Comments: A more recent estimate: 1700 m3/ person/ year. (See above) This would give a minimum water requirement for the world's 6 billion people of 10,200 km3/ year. This apparently does not include water needs for pollution dilution of 23,000 km3/ year (98H1).
(Wastewater Data) By 2000, the world is expected to be generating 2,300 km3 of wastewater a year. It takes at least 10 times that amount to dilute pollutants (98H1).
In 2000, 31 countries (combined population: 508 million) were deemed "water-stressed" or "water-scarce" according to "The State of World Population 2001" report (UN Population Fund). Peter Gleick, an expert on global freshwater problems, in an article in the February 2001 edition of Scientific American wrote 'Roughly half the world's population of nearly 6.2 billion "suffers with water services inferior to those available to the ancient Greeks and Romans." Due to the continued increase in population in developing countries the numbers are expected to rise to about 3 billion people living in 41 countries in 2025. About 2.6 billion people in developing countries lack basic sanitation. Almost 1.5 billion do not have access to clean water. These factors together with preventable water-borne diseases kill over 12 million people/ year ("Water, Water (not) Everywhere", Star-Telegram (Fort Worth TX) (11/2/01)).
(Supply/ Demand) The International Water Management Institute predicts that, by 2025, one third of the world's population (2.7 billion people) will face permanent and severe water scarcity, particularly in Asia and sub-Saharan Africa (01U1).
(Supply/ Demand) 26 nations have water supplies inadequate to support their populations. Nine of these are in the Middle East, 11 are in Africa where 300 million people will be living in drought-stricken areas by 2000 (92P1).
Water Availability in 1990 (in m3/ person/ year) (94G1)
Kuwait ~ ~ ~ ~ ~ | 75 | Qatar~ | 1171
Saudi Arabia ~ ~ |306 | Oman ~ | 1266
United Arab Emir.|308 | Lebanon| 1818
Jordan ~ ~ ~ ~ ~ |327 | Iran ~ | 2025
Yemen~ ~ ~ ~ ~ ~ |445 | Syria~ | 2914
Israel ~ ~ ~ ~ ~ |461 | Iraq ~ | 5531
[A5a] ~ Water Supplies ~ Water Use by Humans ~ Non-Agricultural ~
Agriculture accounts for 66% of human water consumption, industry 20%, and domestic households 10%. The remaining 4% of human consumption of fresh water takes the form of evaporation from reservoirs. (World Water Council data) (09U1).
Water can be used indefinitely in cities and by industry if it is recycled. Comments: This appears to be essentially false. Elsewhere in this review it is pointed that water picks up a certain amount of salt every time it goes through the urban cycle. Salty water requires a desalinization plant to remove the salt after a few cycles through the urban cycle, not just the treatment it gets in a normal water treatment plant now used by typical urban areas to treat river water for distribution to customers.
About 1.1 billion people do not have access to clean water worldwide, and 2.4 billion lack access to sanitation (01M1) Comments: By "sanitation" is probably meant some rudimentary sewage system using underground pipes.
(Power Generation) In industrialized countries, 75% of viable water for electricity generation is used; in Africa 3% is so-used ("World Bank Sees Increased Need to Finance Water Infrastructure", Agence France Presse (1/30/03)).
Groundwater Contribution to Drinking Water use, by Region (00S1)
Region- - - -|Pct.|People Served
- - - - - - -| ~ ~|(millions)Asia-Pacific | 32 |1000-1200
Europe ~ ~ ~ | 75 | 200- 500
Latin America| 29 | ~ ~ ~150
US ~ ~ ~ ~ ~ | 51 | ~ ~ ~135
Australia~ ~ | 15 | ~ ~ ~ ~3
Africa ~ ~ ~ | ~? | ~ ~ ~ ~?World~ ~ ~ ~ | ~ ~|1500-2000
Sources: UNEP. OECD, FAO, US EPA, Australia EPA
Annual water demand by households and industries in developing countries is projected to climb by 590 km3/ year between 1995 and 2020 (Mark W. Rosegrant, Claudia Ringler, "Impact on Food Security and Rural Development of Reallocating Water from Agriculture for Other uses", Harare Expert Group Meeting on Strategic Approaches to Freshwater Management, Harare Zimbabwe, 1/28-31/98).
[A5b] ~ Water Supplies ~ Water Use by Humans ~ Agricultural ~
About 2000 liters of water are required to produce the food we consume each day (presumably a US diet) (05B1). Comments: Is this water use - or water consumption?
Some 1000 tons of water can produce 1 ton of wheat worth at most $200 - or it can expand industrial output by $14,000 (05B1).
Much of the global growth in water use over the past half-century is from a vast increase in irrigation, which is used to produce 60% of the world's grain. Globally, irrigated area nearly tripled between 1950 and 2003, growing from 940,000 to 2.77 million km2. Irrigated area growth is tapering off as the water needed to expand irrigation becomes increasingly scarce. Forty years ago, irrigated area was expanding at an annual rate of 2.1%, but the last 5 years of data reflect slower growth of 0.4%/ year. Since governments are more likely to report gains from new projects than losses as wells go dry, as rivers dry up, and as irrigation water is diverted to cities, these estimates of irrigated area may be high, and the world's irrigated area may have already peaked. (See Figure <http://www.earth-policy.org/Indicators/Water/2006_data.htm#fig1> and Table <http://www.earth-policy.org/Indicators/Water/2006_data.htm#table1>.)
Most people think of improving water productivity in terms of irrigated agriculture, but efforts should not just focus on the 2500 km3 of water diverted annually to irrigation, but must also include the 4500 km3 depleted in rain-fed agriculture. Rain-fed agriculture contributes to about 60% of cereal production on 70% of the global cereal area (04M1).
Researchers from several leading organizations have explored what they consider to be business as usual or base scenarios of future water supply and demand. Looking at the table below you can see that under all four scenarios, irrigation withdrawals increase by 2025 - but with significant differences in by how much (04M1).
Projected Global Increases in Water Withdrawals for Irrigation (in km3).
Source- - -| Total irrigation withdrawals
- - - - - -|1995| 2025|Increase 1995-2025Shiklomanov|2488| 3097| 24%
IWMI ~ ~ ~ |2469| 2915| 18%
FAO**~ ~ ~ |2128| 2420| 14%
IFPRI~ ~ ~ | ~ .| ~ ~.| *4%
**IFPRI number represents projected increase in irrigation depletion, not in irrigation withdrawals.**FAO (03F1) uses 2030 instead of 2025 as the projection year.
Shiklomanov's projection (2000) (00S2) considers present trends and extrapolates them into the future. The IWMI base case (00S3) projects increases in efficiency and productivity in irrigation, but is pessimistic about the amount of gains from purely rain-fed agriculture (without any supplemental irrigation). It also assumes that most countries will opt for food self-sufficiency rather than rely on trade.
The FAO scenario (2002) (04M1) is slightly more optimistic about gains in rain-fed areas, and thus predicts less need for irrigation.
The IFPRI scenario (04M1) is very optimistic about gains in rain-fed areas, particularly in developed countries, and assumes that global food trade will form a significant part of the solution.
Facts and figures from UNESCO's World Water Assessment Program. (3/03?)
Most of this information is based on figures provided by the World Health Organization (WHO).
Each day, 25,000 people die of hunger.
Water requirement equivalent of main food products
Product - - - - - - - |Unit |Equiv. Water, m3/ unitCattle~ ~ ~ ~ ~ ~ ~ ~ |head |4000
Sheep/goats ~ ~ ~ ~ ~ |head | 500
Fresh beef~ ~ ~ ~ ~ ~ | kg. | ~15
Fresh lamb~ ~ ~ ~ ~ ~ | kg. | ~10
Fresh poultry ~ ~ ~ ~ | kg. | ~ 6
Cereals ~ ~ ~ ~ ~ ~ ~ | kg. | ~ 1.5
Citrus fruit~ ~ ~ ~ ~ | kg. | ~ 1
Palm oil~ ~ ~ ~ ~ ~ ~ | kg. | ~ 2
Pulses, roots, tubers | kg. | ~ 1
This table gives examples of water required per unit of major food products. Extracted from the Executive Summary of the WWDR. FAO, 1997. Water Resources of the Near East Region: A Review. Rome.
Irrigation accounts for 70% of fresh water withdrawals, and 30-60% is returned for downstream use (Stanley Wood et al, report released by International Food Policy Research Institute (2/9/01) [satellite data]). Comments: The salt content of this returned water is likely to be significantly larger that what entered the irrigation systems.
The 2.4-fold increase in world grain-land productivity during 1959-1995 was matched by a 2.2-fold increase in irrigation water use (See p. 165 of (99P1)). Comments: productivity or production??? This statement is hard to interpret.
Some 16% of water supply available to irrigate wheat ends up being lost to evaporation (not including transpiration from wheat) (p.170 of (99P1)). Comments: Ref. (99P1) believes that, since rainfall accounts for 10% of wheat's total water supply, actual loss to evaporation may be less.
(Water Constraints on Irrigation) The International Water Management Institute, a CGIAR laboratory in Sri Lanka, projects that by 2025 as many as 39 countries - including northern China, eastern India, and much of Africa - will be forced to reduce irrigation rather than expand it (99M1).
Approximately 70% - 2800 km3 - out of the 4000 km3 of water humans withdraw from global freshwater systems annually ((97S1), p. 69) is used for irrigation ((97W1), p. 9) Comments: What percent of this is consumptive use?
Globally, crops currently get 70% of their water directly from rainfall, and 30% of their water indirectly - from irrigation (99P1). Comments:About 1/6 of the world's croplands (by area) are irrigated.
(Water Needs Trends) Global food-production needs in 2025 could require up to 2000 km3 of additional irrigation water (99P1).
About 70% of fresh water used by humans, globally, is expended for irrigation (Ref. 55 of (94K1)). Comments: Does "used" mean used or consumed?
Agriculture accounted for 72% of global water withdrawals globally, (87% in developing countries) in 1995 (Ref. 46 of (97P2)).
Farming accounts for 70% of global water use (90P1).
Agriculture accounts for 65% of global water use (92P1).
(Water Use Partitioning) Worldwide, agriculture uses about 65% of all water withdrawn from rivers, lakes and aquifers for human activity. 25% goes to industry, 10% goes to households and municipalities (96P1). Comments: Is evaporation from dam backwaters being neglected here. Or is it buried in another figure? It is not negligible.
Average water application rate to irrigated land: 1.2 million m3/ km2 (Ref. 17 of (96P2)), so for 2.4 million km2 of irrigated land, water demand = 2880 km3/ year. Ratio of consumption to withdrawal is 50-80%, so 0.65x 2880 = 1870 km3/ year consumed by irrigation (96P2).
Agriculture's global water-use has increased 5-fold in the 20th century, while population grew only 3.4-fold. Much of this growth in water-use occurred since 1950 (92P1).
Globally, 3300 km3/ year of water are used to water crops (Ref. 20 of (89P1)) (90P1).
Sugar cane consumes about as much water (rainfall + irrigation) as all the world's fruits and vegetables combined (p. 177 of (99P1)).
(Water Use Trends) There has been little or no growth in global irrigation-water supplies since 1990 (Ref. 20 of (96B1)).
History of Global Irrigation Water Use (km3/ year) (Shiklomanov, 1996) (See plot on p. 166 of (99P1))
Year - - - |1940|1950|1960|1970|1980|1990|1995Consumption| 900|1150|1500|1800|2200|2350|2500
Water Withdrawals (km3/ year) for Irrigation and River Runoff (90W1)
(Column 4 = Consumption (km3/ year)) (Col. 5 = Recycled (km3/ year))
Region- - |Area**| With- Col. Col.|River |Gndwater|Surface
- - - - - |Irrig.|drawal= ~4 ~ ~5 |Runoff|Discharg|RunoffEurope~ ~ | 0.17 | 110 = ~95 + 15 | 2321 = ~845 + | 1476
Asia~ ~ ~ | 1.40 |1300 = 980 +320 |10485 = 2879 + | 7606
Africa~ ~ | 0.11 | 120 = ~85 + 35 | 3808 = 1464 + | 2720
N. America| 0.29 | 330 = 215 +115 | 6945 = 2222 + | 4723
S. America| 0.085| ~70 = ~55 + 15 |10377 = 3736 + | 6641
Australia*| 0.020| ~16 = ~13 + ~3 | 2011 = ~483 + | 1528
USSR(fmr.)| 0.20 | 260 = 180 + 80 | 4350 = 1020 + | 3330World Tot.| 2.275|2206 =1623 +583 |40673 =12689 + |27984
* plus Oceania/ ** million km2
Water required for crops in India (cm./ year) (Table 9 and Refs. 54 and 14 of (81G1))
Sugar Cane|140-250| Ground Nuts|60 ~ |Wheat |20-50
Rice~ ~ ~ |120-180| Sorghum~ ~ |50-70|
Corn~ ~ ~ | 50-80 | Cotton ~ ~ |50-70|
Part [A6] ~ Water Supplies ~ Groundwater Supplies ~
A study from the University of Colorado at Boulder says that most of the world's low-lying river deltas are sinking from human activity (oil / gas drilling, over-pumping aquifers etc.), making them increasingly vulnerable to flooding from rivers and ocean storms and putting tens of millions of people at risk. Some 24 out of the world's 33 major deltas are sinking, and 85% have experienced severe flooding in recent years. About 500 million people in the world live on river deltas. Each year about 10 million people are affected by storm surges ((Author Unknown) "World's River Deltas Sinking Due to Human Activity, Says New Study," (9/21/09) New Scientist.).
More than half the world's people live in countries where water tables are falling (07B1). (SU4) (in food-pop-link.doc)
Emptied underground aquifers can be compressed and result in surface subsidence: a problem that is occurring in Bangkok, Venice and Mexico City (07B1).
Globally, the areas most affected by seawater intrusion into freshwater aquifers include Mexico, the northern portions of the Pacific and Atlantic coastlines (of the US), Chile, Peru and Australia. (Science Daily, "Seawater Intrusion is often the Consequence of freshwater aquifer over-exploitation" (7/29/07)) (SU4)
Sana'a, Yemen's capital, has doubled its population on average every six years since 1972 and now stands at 900,000 people. The aquiferon which Sana'a, Yemen's capital, depends is falling by six meters a year, and may be exhausted by 2010, according to the World Bank (Stephen Leahy, "Environment: Millions Flee Floods, Desertification", I.P.S., Brooklin, Canada (10/12/05)). (su4)
Water tables are falling in countries that contain more than half of the world's population (06H1).
Aquifers are being over-exploited in major food-producing regions, including (1) North China Plain (a region that yields half of China's wheat and one third of its corn), (2) Punjab, Haryana, and other highly productive agricultural states in northern India; and (3) the southern Great Plains of the US, a major grain-producing region. Together, China, India, and the US produce nearly half the world's grain. These 3 countries, plus Pakistan, collectively account for over 75% of the world's reported groundwater extraction for agricultural purposes. Falling water tables in these 4 countries make world food production less sustainable. (See Table of Underground Water Depletion in Key Countries <http://www.earth-policy.org/Indicators/Water/2006_data.htm#fig5> .)
Some of the world's largest cities, including Mexico City, Calcutta, and Shanghai, rely heavily on local groundwater. 30% of China's urban water supply is fed from groundwater. Worldwide, roughly 2 billion people - in both rural and urban environments - rely on groundwater for daily water consumption <http://www.earth-policy.org/Indicators/Water/2006_data.htm>.).
If over-pumping of ground water were to cease, the world's grain harvest would fall by 160 million tons - 8% - unless surface water consumption were increased to compensate (Lester R. Brown, Eco-Economy, W. W. Norton and Co., New York (2001) p. 47). Comments:The usual conversion between water and grain is 1000 tons of water per ton of wheat, so this implies a global groundwater overdraft of 160 billion tons of water per year (about 1.44 km3/ year).
(Ground water Inventory Data) The Guarani aquifer, shared by Argentina, Brazil, Paraguay and Uruguay could provide water at 27 gallons/ day to 5.5 billion people for 200 years (03W1).
(Recharge Data) Average recharge rate for the world's aquifers: 0.007%/ year (Ref. 62 of (94K1)).
(Groundwater Depletion Data) The world's continents lose (net) an estimated 190 km3 of groundwater/ year (Ref. 31 of (96G1)) (1994 study). Comments: Postel (99P1) estimates 200 km3/ year (Recharge minus withdrawals).
(Groundwater Depletion Data) 1.5 billion people worldwide rely on groundwater resources, withdrawing 600-700 km3/ year - 20% of globalwater withdrawals ((97S1), pp. 53-54).
Across Africa, Asia, Central- and South America, ground water levels are dropping up to 10 feet a year, due mainly to intensive irrigation. Ground surface levels are sinking in major cities, including Mexico City and Bangkok. Water tables were falling rapidly in South Asia, Mexico and other countries where agriculture relies on irrigation. Two billion people and 40% of agriculture are partly reliant on these hidden stores. Groundwater is rising in Riyadh, Saudi Arabia (due to desalinization plants) ("UN: World's Water Supplies Under Threat", Associated Press (6/4/03).)
(Groundwater Depletion Data) In substantial areas of China and India, groundwater levels are falling by 1-3 meters/ year (03N1).
(Groundwater Depletion Data) In some areas, particularly in the Near East/ North Africa region, irrigation draws on fossil aquifers that receive little or no recharge at a level that is not sustainable (94G1) (03N1).
The world's water deficit is recent - a product of the tripling of water demand over the last half-century and the rapid worldwide spread of powerful diesel and electrically driven pumps. The drilling of millions of wells has pushed water withdrawals beyond the rate of recharge of many aquifers (02B1).
Some 5-8% of global irrigated area depends on non-renewable water or on renewable sources that are pumped faster than they are replenished (Ref. 49 of (97G1)). Comments: Much other irrigation water is subject to being reallocated to urban areas.
Groundwater over-pumping is widespread in central and northern China, northwest and southern India, parts of Pakistan, much of the western US, Northern Africa, the Middle East and the Arabian Peninsula. Ref. (99P1) believes that groundwater over-pumping may now be a bigger threat to irrigated agriculture than the buildup of salt in the soil.
(Groundwater Depletion Data) 1.5 billion people worldwide rely on groundwater resources, withdrawing 600-700 km3/ year - 20% of global water withdrawals (97S1), pp. 53-4).
(Groundwater Depletion Data) Falling water tables from over-pumping of groundwater are ubiquitous in parts of China, India, Mexico, Thailand, the western US, North Africa, and the Middle East (97P3).
(Groundwater Depletion Data) Underground water tables are falling in the southwestern US, the US Great Plains, several states of India (including the Punjab, the country's breadbasket), in much of northern China, across North Africa, in Southern Europe and throughout the Middle East (96B1).
Groundwater Depletion in Major Regions of the World, Circa 1990 (96P1): (su4)
US High Plains: This aquifer underlies nearly 20% of all US irrigated lands. Net depletion to date = 325 km3; Current depletion rate = 12 km3/ year.
California: Current overdraft = 1.6 km3/ year (2/3 in Central Valley)
Southwestern US: Water tables have dropped over 120 m. east of Phoenix. At current rate, water table will drop an added 20 m. by 2020.
Mexico City and Valley of Mexico: Pumping exceeds natural recharge by 50-80%.
Arabian Peninsula: Groundwater use nearly 3 times greater than recharge. Estimated reservoir lifetime at extraction rate projected for the 1990s = 50 years.
African Sahara: Current depletion rate = 10 km3/ year (3.8 km3/ year in Libya alone).
Israel and Gaza: Pumping from the coastal plain aquifer bordering the Mediterranean Sea exceeds recharge by 60%. Salt water has invaded the aquifer.
Spain: 20% of total groundwater use (1 km3/ year) is unsustainable.
India - Punjab (India's breadbasket): Water tables are falling 20 cm./ year across 2/3 of the Punjab.
India - Gujarat: groundwater levels declined in 90% of observation wells during the 1980s.
North China: Water table beneath Beijing has dropped 37 meters. over the past 4 decades. North China's region of groundwater overdraft covers 15,000 km2.
Southeast Asia: Significant overdrafts have occurred in and around Bangkok, Manila and Jakarta. Over-pumping has caused land subsidence beneath Bangkok at 5-10 cm./ year for the past two decades.
Part [A7] - Water Supplies ~ Desalinization ~
Globally, desalinization produces 4.5 km3 of freshwater per year (date not given). Saudi Arabia's 22 desalinization plants produce 1.5 km3of freshwater per year (01T1).
Saudi Arabia has 22 desalinization plants, capable of producing 0.76 km3/ year - 25% of world production of desalinated water. Florida (1992) will produce 0.346 km3/ year. In 1992, a plant in Yuma AZ will produce 0.1 km3/ year (90U1). About 60% of the world's desalinization capacity (2.8 km3/ year) is in the Arabian Peninsula (91A1).
The total cost of producing potable water from seawater is about $1/ m3. Reclamation of moderately polluted water by reverse osmosis costs about $0.13/ m3. The energy required for reverse osmosis is 3 kWH (/1000 gallons?) in theory, 15-30 kWH (/1000 gallons?) in practice. Worldwide, about 4000 desalinization plants produce 4.7 km3/ year of potable water (91A1).
In early 1990 there were 7500 desalinization facilities producing over 13.2 million m3 of water/ day (4.8 km3/ year). Over 50% of this capacity was in the Persian Gulf region (Ref. 41 of (94G1)).
Desalinization Capacity in the Middle East as of 1990 (94G1) (Capacity in m3/ day)
Country - - - -|Capacity~ |Country|CapacitySaudi Arabia ~ |3,568,868 |Iran ~ |260,609
Kuwait ~ ~ ~ ~ |1,390,238 |Oman ~ |186,741
United Arab Em.|1,332,477 |Israel | 70,062
Libya~ ~ ~ ~ ~ | ~619,354 |Egypt~ | 67,728
Iraq ~ ~ ~ ~ ~ | ~323,925 |Jordan | ~8,445
Qatar~ ~ ~ ~ ~ | ~308,611 |Syria~ | ~5,743
Bahrain~ ~ ~ ~ | ~275,767 |Lebanon| ~4,691
Part [A8] ~ Water Supplies ~ Water Recycling ~
In many river basins of the world, especially those that are already experiencing water stress, there is little or no irrigation water being wasted. This due to the prevalence of water recycling and reuse. Egypt's Nile (98M1), (96K1), the Gediz in Turkey (00G1), the Chao Phraya in Thailand (03M1), Bakhra in India (01M2) and the Imperial Valley in California (95K1), are all documented examples. Thus there is less scope for saving water in irrigation than previously thought.
Research suggests that there are low-cost ways to minimize the risks associated with wastewater irrigation and maximize the benefits to the poor (04S1).
At least 5000 km2 of cropland in 15 countries are being irrigated with municipal waste-water (0.2% of the world's irrigated area) (Ref. 27 of (93P2)).
About 70% of Israel's sewage is treated and used as irrigation water for 190 km2 of agricultural land (Ref. 28 of (93P2)).
Israel now reuses 65% of its domestic wastewater for crop production. Treated wastewater accounts for 30% of Israel's agricultural water supply (expected to reach 85% by 2025) (p. 196 of (99P1)).
Part [A9] ~ Water Supplies ~ Irrigation Water-Use Efficiency ~
Global efficiency in land-use has dramatically improved, while agricultural water use efficiency has stagnated due to subsidies, lack of property rights, and government imposed pricing structures that encourage over-exploitation of water resources ((06O1) page 15-32)
Surface water irrigation efficiency ranges between 25 and 40% in India, Mexico, Pakistan and Thailand. It ranges between 40 and 45% in Malaysia, and Morocco. It ranges between 50 and 60% in Israel Japan and Taiwan (05B1).
Traditional furrow irrigation schemes, largely organized by small-scale farmers, cover 80% of irrigated lands in Tanzania's upper Pangani River basin. These methods of irrigation are a major source of conflict because they usually use the water very inefficiently (07M1). (Africa.doc).
As little as 30% of all water diverted into the (irrigation) canals of the Indus River Basin makes it to the root zones of crops.' (page 118 of Ref. (02W1)) (06H2).
In dry areas, deficit irrigation - applying a limited amount of water but at a critical time - can boost productivity of scarce irrigation water by 10 to 20% (03O1).
Of the water used for irrigation, 50-80% is returned to the atmosphere via evaporation or evapo-transpiration or is otherwise lost to downstream users ((93S2), p.19).
Globally, irrigation efficiency (the fraction of irrigation water actually consumed by crops) averaged 43% in 1990 (See Ref. (98S4), p. 25). Irrigation efficiencies in the driest regions run as high as 58%, whereas regions with abundant water supplies have efficiencies as low as 31% ((98S4), p. 25).
Irrigation efficiency in China: 39% ((98S4), p. 25).
Irrigation efficiency in India: 40% ((98S4), p. 25).
Part [A10] ~ Water Supplies ~ Surface Water Supplies ~
Rivers that are drained dry before they reach the sea include Colorado, the major river in the southwestern US, and the Yellow, the largest river in northern China. Other large rivers that either run dry or are reduced to a trickle during dry seasons are the Nile; the Indus, which supplies most of Pakistan's irrigation water; and the Ganges in India's densely populated Gangetic basin. Many of the world's smaller rivers have disappeared entirely (07B1).
More than half the world's 500 mightiest rivers have been seriously depleted. Some have been reduced to a trickle in what the UN warned is a "disaster in the making" (06L1). (su4)
All of the 20 longer rivers of the world are being disrupted by big dams.
One-fifth of all freshwater fish species in the world either face extinction or are already extinct (06L1).
The Nile River and Pakistan's Indus River are greatly reduced by the time they reach the sea (06L1).
The Colorado River and China's Yellow River, now rarely reach the ocean at all (06L1).
The Jordan and the Rio Grande on the US-Mexico border, are dry for much of their length (06L1).
25% of the Britain's 160 chalk rivers and steams - such as the Kennet River in Wiltshire, the Darent River in Kent, and the Wylye River in Wiltshire - are running out of water because too much is being abstracted for homes, industry and agriculture (06L1).
Some 45,000 big dams now block the world's rivers, trapping 15% of all the water that used to flow from the land to the sea. Reservoirs now cover almost 1% of land surface (06L1). Comments: Is this all land (148 million km2) or only ice-free land (131 million km2)?
Half the world's population depends on rivers starting from mountain glaciers as their freshwater source (06H1).
Himalayan glaciers feed 7 major Asian rivers - the Ganges, Indus, Brahmaputra, Salween, Mekong, Yangtze and Huang He - ensuring a year-round water supply for two billion people. But the Himalayan glaciers are retreating (06H1). Comments: Retreating glaciers in the Andes Mountain of South America, the Rocky Mountains of the western US, and Europe's Alps add significantly to the number of people worldwide whose water supplies are being put at risk.
The Chinese Academy of Sciences announced that the Tibetan glaciers are shrinking by 7%/ year. The annual loss of ice is equivalent to the annual flow of China's Yellow River (06H1).
In the Ganges River alone, this loss of glacier melt water could reduce July-September flows by two thirds, causing water shortages for 500 million people and 35% of India's irrigated land (06H1).
In South America, in the dry Andes, glacial melt water contributes more to river flow than rainfall, even during the rainy season (06H1).
The Amu Darya River in Central Asia and the Colorado River in the southwestern US are among the world's rivers that run dry for at least part of the year. Water from the Amu Darya River, once the largest tributary of the Aral Sea, is diverted to irrigate cotton fields of Central Asia. The Colorado's flow is depleted by farmers and cities alike, with over 25% of these withdrawals - 3.8 trillion liters (3.8 km3) - going to California. At times during 18 of the last 26 years of the 20th century, China's Yellow River failed to make it to the sea. In recent years, however, better management and greater reservoir capacity have facilitated year-round flow. Other rivers, including the Ganges, the Indus, and the Nile, are sometimes little more than a trickle by the time they reach the sea. (See Table of Major Rivers Running Dry <http://www.earth-policy.org/Indicators/Water/2006_data.htm#fig3>.)
The Dead Sea has dropped by 25 meters (82 feet) in the past 40 years, and Mono Lake in California has fallen by 11 meters since 1941, the year Los Angeles first began to draw water from its tributaries. Lake Chad once spanning 23,000 km2 in Nigeria, Niger, Cameroon, and Chad. It now covers 900 km2 and exists entirely within Chad's borders, rendering earlier maps obsolete. China's Hebei Province has lost 969 of its 1052 lakes. In Central Asia, historic ports built on the shores of the Aral Sea are now up to 150 kilometers from the water's edge. While the South Aral Sea, intermittently fed by the weakened Amu Darya River, will likely never recover, recent efforts to revitalize the North Aral Sea have raised water level from 30-38 meters, close to the 42-meter level of viability. (See Table of Disappearing Lakes and Shrinking Seas http://www.earth-policy.org/Indicators/Water/2006_data.htm#fig4) (su4)
Both India and China rely heavily on major river systems that have their sources from the glacial melt of the Himalaya Mountains that are now under threat of global warming. Rapid glacial melt cause short term flooding problems, but more importantly will decrease future water supplies for both nations (06H2). (su4)
About 53% of the new water entering the US Great Lakes is ground water; 24% is surface water; 20% is over-lake precipitation subtracting evaporation losses (02R2).
The US Great Lakes cover an area of 94,000 square miles (243,000 km2), and the watershed that drains into them covers 201,000 square miles (521,000 km2). Lake Superior contains 2900 miles3 of water and covers 31,700 miles2. Lake Michigan contains 1180 miles3 of water and covers 22,300 miles2 and has a drainage basin of 45,600 miles2. Lake Erie contains 116 miles3 and covers 9910 miles2 and drains 30,000 miles2. Lake Ontario contains 393 miles3 of water and covers 7340 miles2 and has a drainage basin of 25,000 miles2 (02R2).
The five Great Lakes of the US - Superior, Huron, Michigan, Erie and Ontario - contain over 5500 cubic miles (23,000 km3) of fresh water. This is 18% of the world's available fresh water supply (02R2).
The Ganges, Yellow River, Nile, and Colorado dry up before reaching the ocean, and water that would feed aquifers runs into the ocean without moisturizing forests and marshlands (02U3).
(Lakes) Reuters and the Associated Press ran articles 11/12/01 on the International Conference on Conservation and Management of Lakes meeting, held in Japan to prepare for the Third World Water Forum in 2003. "Up to 1 billion people worldwide depend on endangered lakes, but the number of lakes is shrinking rapidly as growing populations over-tap them for irrigation and drinking water, or over-pollutes them with sewage and industrial runoff," the Associated Press reported. Lakes on the watch list include: the Great Lakes of North America, Lake Victoria in Africa, and the Aral Sea between Kazakstan and Uzbekistan.
(Lakes) Half the world's lakes and reservoirs - representing 90% of all liquid fresh water on the Earth's surface - are degraded by pollution and drainage. Up to 1 billion people worldwide depend on endangered nearby lakes for drinking water, sewage, fishing, irrigation, transportation or tourism, said World Water Forum vice president William Cosgrove (01A1).
Part [A11] ~ Water Supplies ~ Water Losses ~
The cost of fixing aging, leaking water pipes in the US could be $500 billion over the next 30 years (08C1).
Much of today's agriculture in the developing world suffers from large water losses. This holds for both irrigated agriculture, where water use efficiency tends to be of the order of 30%, and for rain-fed agriculture where yields are often of the order of only 100 ton/ km3 or less. The losses tend to be largest in savanna zone agriculture where the majority of the poorest countries are located. There, rain-fed agriculture typically involves water use (consumption?) of the order of 3000 m3/ ton of grain (05F1).
Whereas homes and factories return a large portion of their water to the environment after they use it, half to 2/3 of agriculture's share is "consumed" through evaporation or transpiration and is thus not available for a second or third use (96P3). Comments: Irrigation water returned to the river is usually loaded with salt, making it less useful in downstream irrigation systems.
(Reservoir Evaporation) By 2025 water will be lost through evaporation from reservoirs at a rate of 300 km3/ year, vs.200 in 2000 (03U1).
(Waste) In 2000, global industry wasted 400 km3 of water (03U1).
(Waste) In 2000, global agriculture- and domestic use each wasted water at a rate of 800 km3/ year. (This is expected to become 1000-1100 by 2025) (03U1).
Hydroelectric reservoirs, which greatly expand a river's surface area, can increase water losses through evaporation by 10% of the reservoir's volume annually (98B3). Comments: This rate varies considerably with temperature and aridity. (This data is also in dam data above)
(Reservoir Evaporation) In the US Colorado River, 32% of flow is evaporated from reservoirs (Ref. 23 of (se94D2)), and 64% is consumed by irrigation (se94D2). ("se" means the soils degradation review)
(Irrigation-Related Waste) On average, no more than 50% of water withdrawn for irrigation purposes actually reaches crops. It soaks into unlined irrigation canals, leaks out of pipes and evaporates on its way to the fields (98H1).