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Water is essential not only to survival but is also equally or even
more important than nutrients in food production. Agriculture ac-
counts for nearly 70% of the water consumption, with some es-
timates as high as 85% (Hanasaki
et al
., 2008a,b). Water scarcity
will affect over 1.8 billion people by 2025 (WHO, 2007). This could
have major impacts on health, particularly in rural areas, and thus
also major impacts on farmer productivity. Although of great sig-
nificance, such indirect effects are not considered here. Current
projections suggest that water demand is likely to double by 2050
(Figure 20). Estimates project water withdrawals to increase by 22–
32% by 2025 (De Fraiture
et al
., 2003) and nearly double by 2050,
for all SRES scenarios (Shen
et al
., 2008). For poor countries with
rapid population growth and depletion of groundwater, water-defi-
cit induced food insecurity is a growing problem (Rosegrant and
Cai, 2002; Yang
et al
., 2003). One major factor beyond agricultural,
industrial and urban consumption of water is the destruction of
watersheds and natural water towers, such as forests in watersheds
and wetlands, which also serve as flood buffers (UNEP, 2005).
IMPACTS OF WATER SCARCITY ON YIELD
Studies of 128major river basins and drainage regions show
that approximately 20 to 50% of the mean annual river flow
in different basins needs to be allocated to freshwater-de-
pendent ecosystems in order to maintain them in good eco-
logical condition. In large parts of Asia and North Africa
and some parts of Australia, North America and Europe,
current total direct water withdrawals (primarily for irriga-
tion) already tap into the estimated environmental water re-
quirements (Smakhtin
et al
., 2004). The global consump-
tion of both “blue’’ water (withdrawn for irrigation from
rivers, lakes and aquifers) and “green’’ water (precipitation)
by rainfed and irrigated agriculture and other terrestrial
ecosystems is steadily rising (Rost
et al
., 2008).
Water is probably one of the most limiting factors in increas-
ing food production. Yields on irrigated croplands are, on
average, 2–3 times higher than those on rainfed lands. Ir-
rigated land currently produces 40% of the world’s food on
17% of its land (FAO, 1999), most of it downstream and de-
pendent upon glacial and snowmelt from the Hindu Kush
Himalayas. It is evident that in regions where snow and
glacial mass are the primary sources of water for irrigation,
such as in Central Asia, parts of the Himalayas Hindu Kush,
China, India, Pakistan and parts of the Andes, melting will
eventually lead to dramatic declines in the water available for
irrigation, and hence, food production (Figure 21).
The melting glaciers will impact certain countries more than
others, and also substantially impact hydropower production.
The Indus River and its tributaries, for example, in addition
to providing nearly 60% of the water utilized for irrigation,
also provide 45% of the electrical energy in Pakistan.
Of great importance, therefore, is the effect of climate change
on the extent of snow and glacial mass (UNEP, 2007) and
on the subsequent supply of water for irrigation. Climate
change could seriously endanger the current food produc-
tion potential, such as in the Greater Himalayas Hindu Kush
region and in Central Asia (Figure 21). Currently, nearly 35%
of the crop production in Afghanistan, Bangladesh, Bhutan,
China, India, Myanmar, Nepal and Pakistan is based on ir-
rigation, sustaining over 2.5 billion people. Here, water de-
mand is projected to increase by at least 70–90% by 2050.
Increase, over 2002
water requirements,
needed to meet the
2015 hunger target
Increases, over
2002 water
requirements,
needed to eradicate
poverty by 2030 and
2050 respectively
2 000
0
4 000
6 000
8 000
1960
1970
1980
1990
2002
2015
2030
2050
Water requirements
for food production
(km
3
/year)
Figure 20: Historic and projected changes in water consumption for
food production, 1960-2050.
(Source: ).