Page 102 - Climate Change and Food Systems

climate change and food systems: global assessments and implications for food security and trade
ranging from 30- 40 percent under the low- and high-emission scenarios. The economic model predicts yield declines for more than twice that number of plots in the high-emission scenario, but with an average yield decline of only 13 percent because farmers are allowed to respond to severe climate change with adjustments that prevent large crop failures. Under the low-emission scenario, yields actually increase slightly for most plots. These differences illustrate the importance of a “responsive farmer” assumption in climate change analysis and the potential ability of farmers to adjust to climate change.
One of the criticisms of these types of
models is the often simplistic way they approach adaptation in their models. The above IMPACT model treats adaptation indirectly simply by exogenously raising the rate of agricultural productivity and water use efficiency. Because most adaptation occurs in response to extreme events, as opposed to gradual climate change, which is much harder to detect, most IAM type models (which are better suited for gradual climate change and less so for abrupt extreme events) tend to understate the impacts of climate change and overstate producers’ adaptation response (Patt et al., 2010).
■ Water
As agriculture is the largest water user, modelling agricultural water use and crop water demand are critical to climate impact analysis. Climate
is expected to increase irrigation requirements globally, particularly in semi-arid and arid areas where precipitation is also expected to decline, such as North Africa (IPCC, 2008). Döll (2002) computed irrigation water requirements under climate conditions for the 2020s and the 2070s, and concluded that global irrigation requirements will rise by 3–5 percent in the 2020s and by
5–8 percent in the 2070s, and that the increase will affect two-thirds of the global area equipped for irrigation.
According to Döll et al. (2012), ground water accounts globally for 36 percent of domestic water uses, 42 percent of agricultural water
uses, and 27 percent of industrial water uses.10 Groundwater levels of many aquifers around the world have shown a decreasing trend over the last few decades due to pumping that surpass the groundwater recharge rates, and not to a climate-related decrease in groundwater recharge (Bates et al., 2008). Where the depth of the
water table increases and groundwater recharge declines, wetlands dependent on aquifers are jeopardized and the base flow runoff in rivers during dry seasons is reduced.
Climate change affects groundwater
recharge rates and depths of groundwater tables (Bates et al., 2008). As many ground waters
both change into and are recharged from surface water, impacts of surface water flow regimes
are expected to affect groundwater. Increased precipitation variability may decrease groundwater recharge in humid areas because more frequent heavy precipitation events may result in the infiltration capacity of the soil being exceeded
more often. In semi-arid and arid areas, however, increased precipitation variability may increase groundwater recharge, due to higher rate infiltration from high-intensity rainfalls than evaporation. As
a result of climate change, in many aquifers of the world the spring recharge shifts towards winter and summer recharge declines. Climate-related changes in groundwater recharges have not been observed. This is partly due to lack of data and the slow reaction of groundwater systems to changing recharge conditions.
Economists argue that water markets and water pricing regimes can be effective adaptation tools and can help facilitate water transfer
from lower to higher-valued uses (Saliba and
10 Satellite remote sensing is deployed increasingly
to estimate groundwater quantities at the global level. Since 2002, the NASA/GFZ Gravity Recovery and Climate Experiment (GRACE) has been providing means to investigate groundwater storage changes through high-precision satellite gravimetry (Ramillien et al., 2008). The GRACE data have
been applied to investigate regional groundwater situations, in many regions including California (Famiglietti et al., 2011), the Central United States (Strassberg et al., 2009), and India (Rodell et al., 2009).
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