Agriculture Reference
In-Depth Information
structures such as earth dams or water pans
can be considered. Water can be supplied to
crop land either by gravity or pumping and
applied to crops either by surface irrigation
(furrow or basin) or pressurized irrigation
(especially low-head irrigation systems).
Other rainwater harvesting structures such as
sand dams, subsurface dams, and rock catch-
ment systems fall under this category.
Spate irrigation - fl ood diversion and spread-
ing into crop land is appropriate in areas where
fl ash fl oods occur, especially in lowlands adja-
cent to degraded or rocky catchments.
Micro-irrigation systems - these include vari-
ous technologies, among which low-head drip
irrigation kits are the most appropriate. Low-
head drip kits can use many different water
sources. They are mainly used for irrigating
high-value crops like garden vegetables and
orchard fruits and for green maize production
at times.
Land drainage, wetland management, and
fl ood recession are appropriate for areas with
excess soil moisture and should therefore be
considered where necessary.
On the demand side, water-use effi ciency,
through, for example, recycling of water, is
the main adaptation intervention. Greater use
of economic incentives, including metering
and pricing, can encourage water conservation
and the reallocation of water to highly valued
uses (IWMI
2007
).
On the supply side, more strategic water stor-
age is a key intervention for the adaptation of
agriculture to climate change. Water storage
provides a buffer and can offset the risks asso-
ciated with fl oods or droughts. Water storage
options include reservoirs, ponds, tanks, aqui-
fers, soil moisture, and natural wetlands
(McCartney and Smakhtin
2010
).
The rate of glacier deposition and melting
under climate change will be a major determi-
nant of water availability for agriculture, but
remains highly uncertain and under-studied.
In China, for example, the best current knowl-
edge is that runoff from glaciers may peak
from 2030 to 2050, followed by a gradual
decline (Piao et al.
2010
).
Irrigation will be an important adaptation
option in some regions. It compensates both
for long-term declines in water supply and for
short-term defi cits associated with increasing
climate variability. This will be the key for
Brazil, for example (Rosenzweig et al.
2004
;
Cunha et al.
2012
).
Irrigation will not work as an adaptation
option everywhere. In sub-Saharan Africa,
water supply reliability (ratio of water con-
sumption to requirements) is expected to
worsen and will limit the adaptation potential
of irrigation. Even farming regions that are
expected to have suffi cient water under cli-
mate change, such as the Danube basin of
Europe, may not be able to expand irrigation
for adaptation strategy, as models suggest that
this would increase water supply unreliability
(Rosenzweig et al.
2004
).
Climate change mitigation measures, such as
reforestation, can assist adaptation by increas-
ing the capacity of soils and landscapes to
hold water (Thornton and Cramer
2012
).
There are several methods of applying irriga-
tion water and the choice depends on the crop,
water supply, soil characteristics, and topogra-
phy. Surface irrigation methods are utilized in
more than 80 % of the world's irrigated lands, yet
its fi eld-level application effi ciency is often
40-50 %. To generate income and alleviate pov-
erty of the small farmers, promotion of afford-
able, small-scale drip irrigation technologies are
essential. Drip irrigation minimizes water losses
due to runoff, and deep percolation and water
savings of 50-80 % are achieved when compared
to most traditional surface irrigation methods.
Crop production per unit of water consumed by
plant evapotranspiration is typically increased by
10-50 %. Thus, more plants can be irrigated per
unit of water by drip irrigation and with less
labor. The water-use effi ciency by chili pepper
was signifi cantly higher in drip irrigation com-
pared to furrow irrigation, with higher effi cien-
cies observed with high delivery rate drip
irrigation regimes (AVRDC
2005
). For drought-
tolerant crops like watermelon, yield differences
between furrow and drip irrigated crops were not
signifi cantly different; however, the incidence of
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