Managing Scarce Water Resources in Agriculture in West Asia and North Africa - Restorative Redevelopment of Devastated Ecocultural Landscapes - page 441

DECLINING AGRICULTURAL SHARE OF WATER
The world contains an estimated 1,400 million cubic km of water. Only 0.003 percent
of this vast amount, about 45,000 cubic km, is what we call “freshwater resources,”
which is water that theoretically can be used for drinking, hygiene, agriculture, and
industry. In fact, only about 9,000 to 14,000 cubic km is economically available
for human use—a small amount compared to the total amount of water on earth.
With the population increasing by two billion by 2030, the question is: will there be
enough water to sustain human life?
Agriculture is by far the largest user of water, accounting for about 70 percent
of all withdrawals from rivers, lakes, and aquifers, and up to 95 percent in many
developing countries. Currently, agriculture consumes about 80 percent of water
resources in the WANA region. This share is decreasing not only because of fast
population growth, but also due to diversions to domestic and industrial sectors and
to maintain ecosystems. In North African countries it is projected that agricultural
share will drop to about 70 percent and 50 percent by the years 2025 and 2050,
respectively (Figure 22.3).
The amount of water used in food production is significant, and most of it is sup-
plied directly by rainfall. Based on current average food intake per capita, approxi-
mately 1,000 m 3 water is needed to produce the food per person per year (FAO
2003b). Thus, with a world population of 6 billion, net water needed to produce
enough food for this population is 6,000 km 3 . Most of the water used in agriculture
comes from rainwater stored in the soil profile (green water) and only 15 percent of
water for crop production is provided through irrigation (blue water). Thus, irriga-
tion needs 900 km 3 of water per year for crop production. On average, 40 percent
of water withdrawn from rivers, lakes, and aquifers effectively contributes to crop
production. The remainder (60 percent) is lost through nonbeneficial evaporation,
deep percolation, and through growth of weeds. Therefore, the current global water
withdrawal for irrigation is in the order of 2,000 to 2,500 km 3 per year. Thus, there is
enough freshwater to feed the people of the globe, but the problem it is not uniformly
distributed in space and time and WANA receives the least.
The water needed for crops amounts to 1,000 to 3,000 cubic meters per tonne of
cereal harvested. It takes 1 to 3 tonnes of water to produce 1 kg of grain. Furthermore,
it is estimated that only 45 percent of the water used in agriculture is effectively
used by crops (UN/WWAP 2003). The other 55 percent is partially lost by either
evaporation or by losing quality while joining salt sinks. The other part recharges
aquifers, or flows downstream to be reused. Therefore, agriculture is not seen as the
most efficient water user. The ever-growing competition among water-using sectors
is certainly forcing agriculture to give up part of its share to higher priority uses,
especially the domestic and industrial sectors. Meanwhile, agriculture must cope
with the increasing demand for food, feed, and fiber, but with less water.
In many countries of the world, the challenge, as set by the CGIAR Challenge
Program on Water for Food (CPWF), is to retain diversions of water to agriculture
not higher than the year 2000 level. In WANA the question is how fast it drops below
that target (Figure 22.3).