water relation with food and agriculture

1. The
WORLD,S WATER

2. Water resources
A graphical distribution of the locations of water on
Earth

3. FLOWS OF FRESH WATER
Precipitation Evaporation Runoff MINIMUM
Continent (km/yr) (km/yr) (km3 /yr)
Europe 8,290 5,320 2,970
Asia 32,200 18,100 14,100
Africa 22,300 17,700 4,600
North America 18,300 10,100 8,180
South America 28,400 16,200 12,200
Australia/Ocea
nia
7,080 4,570 2,510
Antarctica 2,310 o 2,310
Total Land
Area
118,880 71,990 46,870
Table 2.2 shows one estimate of the average annual water
balance of major continental areas, including precipitation,
evaporation, and runoff.

4. Quantitative Measures of
Water Availability or Use
The most common absolute measure for a stock of
water is a volume. The most common measure for a
flow of water is a volume per unit time. Thus a stock
of water in a lake or groundwater aquifer can be
measured in km-' or million gallons or thousand acre-
feet. River flow might be measured in km" per year
or cubic feet per second or acre-feet per year or one
of any number of similar units.

5. 0
2000
4000
6000
8000
10000
12000
14000
16000
EUROPE NORTH AND
CENTRAL
AMERICA
AFERICA ASIA SOUTH
AMERICA
AUSTRALIA
AND
OCEANIA
Cubickmperyear
continents
Series 1 Series 2 Series 3

6. International River Basins:
A New Assessment
A critical factor in assessing the world's stocks and flows of
water is the role of political borders in dividing those waters.
Many rivers, lakes, and groundwater aquifers are shared by
two or more nations and most of the renewably available
freshwater of the earth crosses political borders. In 1958, the
United Nations published the first comprehensive collection of
information on shared international rivers of the world (United
Nations 1958).

11. Continent
United Nations
(1978)
Wolfet al, (1999)
Africa 57 60
North and
Centrl America
33 39
South America 36 38
Asia 40 53
Europe 48 71
Totals 214 261
Number of International River Basins,
by Continent

12. The Geopolitics of International
river Basins
 The growing literature on the connections between
international conflicts and water resources primarily
deals with international river basins (see, for example,
Gleick 1993, McCaffrey 1993, Biswas 1994, Dabelko and
Dabelko 1996, Wolf 1998).
Similarly, the bulk of the legal tools that have been
developed to address water disputes also deal with
international river basins. As a result, the new data
described above will be vitally important for
understanding and resolving future political and
military conflicts over water.

13. SUMMARY
 Recent experience suggests that conflicts may be more
likely to occur on the local and regional level than between
nations, and in developing countries where common
property resources like water may be both more critical to
survival and less easily replaced or supplemented. As a
result, better information is still required
on disputed waters within existing national borders-not just
information on shared international watersheds. Moreover,
water-related threats to security depend not just upon the
geophysical characteristics of watersheds and the
hydrologic cycle, but also upon the economic, cultural, and
sociopolitical factors at work in a given country or region.
Policymakers must be alert to the likelihood of
disagreements over water resources and to the kinds of
legal, economic, political, and technical responses that can
minimize the risk of conflict.

14. Water for Food: How
Much Will Be Needed?
 One of the most vital questions facing society is
whether or not we will be able to produce enough food
for future populations. Reviewing the literature and
science behind this problem, evaluating the resources
that are available or may be needed, and predicting the
behavior and actions of growers, governments, and
markets addressing food needs, leads to one definitive
answer: we do not know. Those who reach a firm
conclusion that we either will or will not be able to
feed future populations are unreasonably optimistic
about their ability to predict the future.

15. Total Water Required to Produce
Regional Diets, Late 1980s
Region
Water to
Produce
Average Diet
(liters/pl d)
Water to
Produce
Average Diet
(m3 /p /yr )
Africa, South of Sahara
Centrally Planned Asia
Eastern Europe
Former USSR
Latin America
Middle East/North Africa
OECD-PacificIOceania
South and East Asia
Western Europe
North America
1,760
2,530
3,910
4,300
2,810
2,940
3,310
2,110
4,690
5,020
640
920
1,430
1,570
1,030
1,070
1,210
770
1,710
1,830
.
Glieck 1997

16. Water Required to Produce
Average Diets
0
200
400
600
800
1000
1200
1400
1600
1800
2000
aferica central
asia
eastern
europe
latin
america
north
aferica
south and
east asia
western
europe
north
america
m3/p/year
continents
Chart Title
Series 1 Series 2 Series 3

17. How Much Food Will People Need
and Want to Eat?
 Almost as important as the number of people is how much
food these people will need and desire. Needs and wants
are not the same thing. Richer countries and individuals
can, and do, eat considerably more than required to satisfy
basic food needs. Here, however, a minimum amount of
food can be-and has been established. The UNFAO sets
minimum requirements for a healthy and productive life at
2,200 to 2,300 calories per person per day. If the world
population in 2050 is between 7.3 and 10.7 billion people,
meeting a minimum caloric requirement of 2,200 calories
per day will require the production of 16 to 24 trillion
consumable calories per day worldwide. Adopting the UN
mid-range population estimate of 8.9 billion people in 2050
means the world will have to produce nearly 20 trillion
consumable calories per day. Current production is around
14 trillion calories.

18. Region
Mai
ze
Soybe
an
Wheat Rice
Pulse
s
Roots
Veget
ables
fruits oils
Anima
l fat
Africa.
South
351 237 195 281 81 332 21 90 169 22
C asia 118 43 380 1143 51 144 43 40 59 39
Eastern
Europe
143 0 1095 32 39 100 74 74 269 274
Former
USSR
3 16 1043 72 17 180 56 54 248 219
Latin
Americ
a
274 13 438 256 69 124 30 133 220 63
Middle
East!
84 28 1103 203 69 68 70 137 339 47
OECD-
Pacific/
42 12 492 315 25 326 49 147 209 98
s/e asia 87 41 315 1075 51 62 39 57 190 30
Wester
n
Europe
37 0 647 43 25 151 70 123 383 243
North
Americ
a
27 2 537 112 28 81 105 146 364 129
Average Regional Diets, 1989 (Calories per person
per day)

19. What Kind of Food Will They Eat?
 Preferences for food vary from region to region and culture to
culture. Food analysts note that urban populations have
different food preferences and that the rapid growth of urban
centers coupled with rising incomes in both rural and urban
areas will affect food demands. Urbanization especially leads
to a shift to more diversified diets away from grain staples to
processed foods, meats, milk, and fruits and vegetables
(Pandya-Lorch 1999). The calories needed or desired by people
can be provided in many ways, with different combinations of
livestock, crop, and fish products. Table 4.2 shows a
breakdown of how today's diet is met in the major regions of
the world. Even a cursory glance at these data reveals
tremendous variations in preferences and food
priorities.

20. Shee
p
Beef Pig
Poultr
y
Eggs Milk Fish
Alcoh
ol
sweet
Other
s
Cal/d
ay
from
Meat
14 36 25 15 6 67 25 51 145 25 2191 10
68 45 104 10 17 36 25 52 82 43 2541 15
20 79 202 47 50 250 15 165 381 37 3345 28
15 205 91 42 59 244 73 133 458 25 3253 30
11 89 50 65 20 156 30 78 401 34 2555 19
48 41 2 45 24 125 15 12 308 51 2819 13
57 90 96 64 28 118 71 80 329 43 2691 24
3 23 61 38 18 60 51 43 202 38 2485 12
30 116 307 47 49 342 54 189 413 80 3350 36
21 232 202 136 46 267 48 154 431 68 3133 35

21. What Quality Will That Land Be?
One of the most critical soil-quality problems-particularly
related to water-is the increase in concentration of total
dissolved solids, commonly referred to as salinization.
Natural processes or human activities can salinize lands. In
extreme cases, irrigation water can contain as much as one
to 3.5 tons of salt per 1,000 m", Since crops can need 6,000
to 10,000 m3 of water per hectare, land can receive tens
of tons of salt per hectare (Crosson and Rosenberg
1989).As this water evaporates, it leaves behind the salts.
Excessive waterlogging of soils can also salinize lands by
bringing salts to the surface and concentrating them. Tables
13 and 14 in the Data Seeton describe the extent of
salinization worldwide

22. Irrigated land affected by salinization
0
5
10
15
20
25
30
35
40
45
PERCENT
COUNTRIES
Chart Title
Series 1 Series 2 Series 3

23. What Fraction of Crop Production
Is Actually Eaten by Humans?
Most projections or predictions of future food production
stop at how much food can be grown in the field. But this is
only a piece of the puzzle. Not all crops grown can be
successfully harvested. Severe weather can wipe out a crop
or reduce its value. There are inefficiencies in harvesting
that leave part of every crop in the field. Insects, diseases,
and weeds destroy around a third of all crop production. For
example, as much as 24 percent of grains harvested in
Kenya are subsequently lost.

24. Category Percentage of Rice Lost
Harvest 1 to 3
Handling 2 to 7
Threshing 2 to 6
Drying 1 t05
Storage 2 to 6
Transport 2 to 10
Total Range 10 to 37
Post-Harvest Losses
from Rice Production
Source: http://www.fao.org/News/FACTFILE/
FF9712-E.HTM
Notes: In some regions of Africa and Latin
America as much as 50 percent of cereal and
legume harvests are lost. Losses of 10 to 15 percent are considered

25. How Much Water Is Necessary to
Grow Different Crops?
Different crops require different amounts of water. Crops
transpire amounts of water that depend on their
physiological requirements, climate, soil conditions,
and location. The total amount of water required to produce
food depends on the kinds of crops that will be grown, their
water requirements, and agricultural practices. Growing a
ton of corn may require between 1,000 and 2,000 tons of
water; a ton of rice may require 2,000 to 5,000 thousand
tons of water; a ton of cotton may require as much as 15,000
tons of water (Pimental et al. 1997).Table 4.7 lists
approximate water requirements to produce a kilogram of
various important crops. Actual values vary with a wide
range of factors.

26. Approximate Crop Water Requirements
to Produce Food Harvested
CROP KG OF WATER/KG OF FOOD
POTATO 500 to 1500
WHEAT 900 to 20000
SORGHUM 1100 to 1800
CORN 1000 to 1800
RICE 1900 to 5000
SOABEANS 1100 to 2000
BEEF 15000 to 70000

27. How Will Crops Be Irrigated?
There are many forms of irrigation and types of irrigation
technology, ranging from poorly controlled flood irrigation to
computer-controlled drip irrigation. Different crops have
different irrigation requirements. Different irrigation
technologies have different irrigation efficiencies and vastly
different economic costs. The efficiency with which irrigation
water is used varies by region, crop, agricultural practice, and
technology. In many places less than half of all water applied
to a field is used productively by the crop. The rest is lost to
unproductive evaporation or to groundwater, where it mayor
may not be recovered for other uses.

28. Irrigation Approaches
surface irrigation
• Surface irrigation or field flooding of large areas is
widely used because of low capital costs and long
experience.

29. Irrigation Approaches
Furrow irrigation, practiced since ancient times, involves digging
numerous U- or v shaped furrows through irrigated land and
introducing water into them from a channel at the top of a field. As with
other surface techniques, water ponds on a field and both evaporates
unproductively to the air and infiltrates to groundwater.
Border irrigation involves flooding land in long parallel strips
separated by earth banks built lengthwise in the direction of the slope of
the land. Water flows from the highest point in the field to the lowest.
Basin irrigation is similar to border irrigation
but includes earth banks constructed crosswise
to those used for border irrigation, dividing a
field into a series of basins that can be separately irrigated.

30. Irrigation Approaches

31. Irrigation Approaches
Sprinkler systems vary in type, capabilities, and cost. Typical
systems include water pumps, main lines, smaller lines, and sprinkler
heads. Water sprays over crops or land surfaces providing an even
distribution of water. Sprinklers are suitable for a wide range of soils,
crops, and terrain. They can be portable or permanent. In recent years,
a wide variety of precision sprinkler technologies have been developed
and are increasingly widely used. These systems greatly improve the
ability to precisely deliver water when and where it is needed, at a cost
typically higher than traditional sprinklers. Some fraction of the water
applied is still lost to unproductive evaporation.

32. Irrigation Approaches
 Drip irrigation involves the use of lowvolume water
emitters placed precisely where crops need water.
Components of drip systems include pumps, filters,
main lines, lateral lines, and emitters or drip heads.
Chemicals can often be added to the water and
precisely applied at the same time as the water. When
soil moisture is carefully monitored, applications of
water can be very carefully controlled. Drip systems are
suitable for permanent crops, such as vineyards and
orchards, and increasingly are being applied to row
crops. In California, farmers are even experimenting
with using drip systems on crop .

33. Examples of Productivity Gains
Crop Change in crop yield% Change in water% Change in outcome %
Banana 52 -45 173
Cabbage 2 -60 150
Cotton 27 -53 169
Cotton 25 -60 255
Grapes 23 -48 134
Potato 46 0 46
Sugarcane 6 -60 163
Sugarcane 20 -30 70
Sugarcane 29 -47 91
Sugarcane 33 -65 205
Sweet potato 39 -60 243
Tomato 5 -27 49
Tomato 50 -39 145
Shifting to Drip from Conventional Surface
Irrigation, India, Mid-1990s

34. What Kind of Water Will Be Used
to Grow Food?
 Not all water is the same. Agriculture can use direct
rainfall, direct streamflow, water stored in lakes and
reservoirs, high-quality fossil groundwater, rapid-recharge
groundwater, brackish surface or groundwater, reclaimed
and recycled wastewater, and under some circumstances,
even untreated wastewater or seawater. The kinds of
water that will be desired, available, and used to grow the
crop mix of the future remain highly uncertain. In Israel,
for example, there is talk of devoting all primary water
supplies to urban uses, with agriculture being forced to use
only reclaimed and recycled water .

35. How Will Climatic Change Affect
These Factors?
 What the ultimate impacts of climate change will be on
water availability, water quality, agricultural water
demand, crop yields, and overall food production are
still the domain of speculation and research.
Nevertheless, answering the initial questions
about how much food will be needed to feed the world
and how much water it will take to grow it requires that
we also know the answers to how climate change will
affect the food/water equation. Among the many
factors that must be considered are the role of
increasing CO2 on crop water needs and crop yields

36. How Will Climatic Change Affect
These Factors?
 the direct effects of temperature and precipitation
changes on yields, and how severe events
may change. Climate change will alter rainfall,
temperature, runoff, and soil moisture, as well
as the nature and severity of extreme events. Increased
evaporation and transpiration from soils and plants will
cause moisture stress and changes in flowering,
pollination, and grain-development success (Rosenzweig
and Parry 1994)

37. CONCLUSIONS
 But ultimately, there are two slightly different questions
that must also be asked and answered. How much food will
be needed, not to meet overall demands, but to
meet the basic needs of all humans? and how much water
will it take to meet that need? These two questions
emphasize the difference between human desires and basic
needs.
We must begin serious efforts to integrate information on
diets, basic food needs, meat consumption, agricultural
water-use efficiency and technology, cropping patterns,
land use, genetic engineering, water pricing, and even
population policies. Addressing these problems in isolation
only increases the risk that basic human needs will
continue to be un met for hundreds of millions of people.

38. Thank you