Regional Impacts - Climate Resilient Agriculture for Ensuring Food Security - page 100

the fi rst few decades of this century, moderate
climate change would increase aggregate yields
of rainfed agriculture by 5-20 %, but with impor-
tant variability among regions. Major challenges
were projected for crops that are near the warm
end of their suitable range or which depend on
highly utilized water resources.
Research since the TAR supports the conclusion
that moderate climate change will be likely to
increase yields of North American rainfed agricul-
ture, but with smaller increases and more spatial
variability than in earlier estimates (high confi dence)
(Reilly et al. 2001 ). Many crops that are currently
near climate thresholds, however, are projected to
suffer decreases in yields, quality, or both, with
even modest warming (medium confi dence).
The vulnerability of North American agriculture
to climatic change is multidimensional and is
determined by interactions between preexisting
conditions, indirect stresses stemming from
climate change (e.g., changes in pest competition,
water availability), and the sector's capacity to
cope with multiple, interacting factors, including
economic competition from other regions as well
as improvements in crop cultivars and farm
management. Water availability is the major fac-
tor limiting agriculture in southeast Arizona, but
farmers in the region perceive that technologies
and adaptations such as crop insurance have
recently decreased vulnerability. Areas with
marginal fi nancial and resource endowments
(e.g., the US northern plains) are especially vul-
nerable to climate change. Unsustainable land-
use practices will tend to increase the vulnerability
of agriculture in the US Great Plains to climate
change. Heavily utilized groundwater-based
systems in the southwest USA are likely to expe-
rience additional stress from climate change that
leads to decreased recharge (high confi dence),
thereby impacting agricultural productivity.
Decreases in snow cover and more winter rain
on bare soil are likely to lengthen the erosion sea-
son and enhance erosion, increasing the potential
for water quality impacts in agricultural areas.
Soil management practices (e.g., crop residue,
no-till) in the North American grain belt may not
provide suffi cient erosion protection against
future intense precipitation and associated runoff.

5.6 North America

• Rainfed agriculture is likely to increase yields
by 5-20 % in the early decades of the century,
but with important variability among regions.
• Water resources will be affected by warming in
western mountains which will lead to decreased
snowpack, more winter fl ooding, and reduced
summer fl ows, exacerbating competition for
over-allocated water resources.
• Crops near the warm end of their suitable
range, such as wine grapes, or those that
depend on highly utilized water resources will
face major challenges.
• Forest growth is likely to increase 10-20 %
overall during the twenty-fi rst century as a
result of extended growing seasons and CO 2
elevation, although with important spatiotem-
poral variation. Forests are likely to be affected
by changes in disturbances from insects, diseases,
and wild fi res and associated losses depending
on the emission scenario.
• Cold-water fi sheries are likely to be negatively
affected, while warm-water fi sheries will gen-
erally gain with mixed results for cool-water
fi sheries. Higher temperatures will lead to
northward shifts of species distribution.
As the rate of warming accelerates during the
coming decades, changes can be anticipated in
the timing, volume, quality, and spatial distribution
of freshwater available for human settlements,
agriculture, and industrial users in most regions of
North America. While some of the water resource
changes listed above hold true for much of North
America, twentieth-century trends suggest a
high degree of regional variability in the impacts
of climate change on runoff, stream fl ow, and
groundwater recharge. Variations in wealth and
geography also contribute to an uneven distribution
of likely impacts, vulnerabilities, and capacities to
adapt in both Canada and the USA.
A number of studies have been produced
which assess the impacts of climate change on
agriculture in North America. The IPCC Fourth
Assessment Report of agricultural impacts in
the region cites 26 different studies. With high
confi dence, the IPCC ( 2007 ) projected that over