Water scarcity and abundance, water productivity and their relation to poverty - Water Scarcity, Livelihoods and Food Security - page 32

irrigation systems. It is less useful to identify inefficient rainfed cropping
systems, except in the broadest sense; for example, rainfed agriculture in West
Africa clearly performs poorly. It is more useful to analyze the reasons why it
performs so poorly.
WP still remains an important identifier of efficiency in irrigated systems; for
instance the WP of the huge Gezira irrigation area in Sudan was low as a result
of central control, which prescribed crop management and required that the
tenant farmers plant 20 percent of their land to cotton. Recent administrative
changes allow some crop diversification and WP is improving, but remains low
(Awulachew et al., 2012a; 2012b). In contrast, there are bright spots in the
Indian Punjab in the Ganges Basin, where WP is close to its practical maxi-
mum (Sharma et al. , 2012). When we apply the concept of WP to rainfed
systems, the results are trivial because only a small proportion of the precipita-
tion is used by agriculture.
There are wide variations in WP in rainfed systems within basins, for
example, the Volta (Lemoalle and de Condappa, 2012), the Karkheh (Ahmad
and Giordano, 2012) and the Limpopo (Sullivan and Sibanda, 2012). Each
basin needs careful analysis to identify the causal factors, which differ between
basins, so that it is impossible to make blanket recommendations. Focus on
WP can (and did) overshadow other, equally important indicators of produc-
tivity and livelihoods, which partly explains why the CPWF focus broadened
from water scarcity to include development challenges.
Final observations
Authors often write that “drought tolerance” can improve WP, although the
term is rarely explained. Certainly crops or crop varieties that are able to
survive short droughts without too much damage are likely to give yields that
are more reliable in droughty environments than those that cannot. However,
gains in WP through new germplasm are most likely when plants are capable
of yielding well under favorable climatic conditions as well as being tolerant of
drought and other abiotic stresses. Reliable yields under dry conditions are
only half of the story.
Much of the improvements in yield (and hence WP) last century were
achieved by plant breeders who changed harvest index, that is, the proportion
of the commercial product (often grain) in the total yield (Gifford and Evans,
1981; Bennett, 2003). They achieved this by breeding short-strawed rice and
wheat, and hybrid sorghum and maize with shorter stature and reduced root
systems, which were possible on good soils with precision fertilizer placement.
In rainfed agriculture in many of the CPWF's target basins, smallholder farmers
typically grow rustic varieties with low harvest indices. High-yielding plant
varieties and fertilizer can increase WP, but the institutional and sociological
problems that constrain farmers from adopting them are the key issues. There
is also the issue of varietal adaptation: modern varieties do sometimes perform
poorly when grown under stresses to which they lack adaptation. Nonetheless,