Managing Scarce Water Resources in Agriculture in West Asia and North Africa - Restorative Redevelopment of Devastated Ecocultural Landscapes - page 455

intensity of rainfall (with large spatial and temporal variability) rather than to low
cumulative volume of rainfall. The key challenges lie in mitigating the risk of the
intra-seasonal dry spells in order to improve water productivity The technologies
that have been proven to be successful in this regard are water harvesting, supple-
mental irrigation, and a combination of both. Equally important is addressing farm-
ers' perceptions of risk and adapting these technologies, management strategies, and
policies that address their concerns.
Simulation models for forecasting world food future and water use anticipate that
basin water productivity in the developing countries will increase for both irrigated
and rainfed agriculture in order to cope with the sharp increase in food demand.
Using 1995 data as a base, it is anticipated that WP in the developing countries will
increase from 0.45 kg/m 3 to 0.55 kg/m 3 by 2025 for rainfed cereals (excluding rice)
and from 0.56 kg/m 3 to 0.93 kg/m 3 for irrigated cereals over the same period. This
represents an increase in WP of 22 percent and 66 percent for the rainfed and irri-
gated cereals, respectively.
Precipitation in the dry rainfed areas, especially in the Mediterranean-type
climate, is characterized by low annual amount, unfavorable distribution over the
growing season, and great fluctuation among years. Except in limited areas and
exceptional years, rainfall amount in the dry areas is much lower than crop water
requirements for economic production. Furthermore, the distribution of the rain in
these areas is irregular, unpredictable, and does not usually match crop needs (Figure
22.4). The suboptimal distribution of rainfall coupled with great variations from year
to year make predictions very difficult.
As a result of unfavorable rainfall characteristics, soil moisture does not satisfy
crop needs over the whole season. I will take wheat as an example here. In the
wet months (Dec. to Feb.) stored rain is ample, crops sown at the beginning of the
season are in early growth stages, and water extraction rate from root zone is very
low. Usually little or no moisture stress occurs during this period. However, in early
spring, crops grow faster, demanding a high rate of evapotranspiration and soil mois-
ture depletion. Usually, at that time chances of rain become little while soil moisture
drops below critical levels. Thus, a stage of increasing moisture stress starts and con-
tinues until the end of the season. This moisture stress occurs in all Mediterranean-
type rainfed areas with no exception but varies in its starting time and severity.
As a result, rainfed yields are very low in all countries of the region. Potential
yields are much higher and are attainable if soil moisture stress during dry spills
is alleviated. Supplemental irrigation is an effective response to this problem. This is
the addition of essentially rainfed crops of small amounts of water during times when
rainfall fails to provide sufficient moisture for normal plant growth, in order to improve
and stabilize yields.
Research results from ICARDA and other institutions in the dry areas as well as
harvest from farmers showed substantial increases in rainfed crop yields in response
to the application of relatively small amounts of water. This increase covers cases
with low as well as high rainfall. Average increases in wheat grain yield under low,
medium, and high annual rainfall in Aleppo reached about 400 percent, 150 percent,
and 30 percent using amounts of SI of about 180, 125, and 75 mm, respectively
(Figure 22.5). When rainfall is low, more water is needed but the response is greater,