Agriculture Reference
In-Depth Information
Table 4.10
Infl uence
of climate change and development on water supply and demand (Turral et al.
2011
)
Elements of the
water cycle
Impact from
Development activities
Climate change
Annual
precipitation
No or minor impact
Expected to increase globally during the
twenty-fi rst century, with potentially great
spatial variations
Interannual
variations in
precipitations
No impact
Expected to increase everywhere
Seasonal
variability of
rainfall
No impact
Expected to increase everywhere
Soil moisture
stress (droughts)
Limited impact: some agricultural practices
can deplete soil moisture faster than natural
vegetation
Moisture stress to generally increase as a
result of increasing variability of rainfall
distribution (longer periods without rain) and
increasing temperatures
Floods
Moderate impact: fl ood intensity and impact
can be exacerbated by changes in land use
and unplanned development in alluvial plains
Increased as a result of increasing frequency
and intensity of extreme rainfall events
Snow and glacier
melt
Limited impact through deposit of pollutants
and change in the refl ecting power of the
surface (albedo)
Rising temperatures lead to accelerated snow
and glacier melt with initial increases in river
fl ow followed by decreases
River discharge
High impact in water scarce areas, where
reservoir construction and water diversion
for agriculture and other uses are modifying
runoff regimes and reducing annual fl ow.
Large-scale water conservation measures
also have an impact on river discharge
Increased variability as a result of changes in
rainfall patterns. Changes in snow and glacier
melt induce changes in seasonal patterns of
runoff. Changes in annual runoff expected to
vary from region to region
Groundwater
High impact: large-scale development of
groundwater resources in many regions is
already threatening the sustainability of
aquifers in many dry areas
Varies as a function of changes in rainfall
volumes and distribution. Impact is complex,
with fl oods contributing to increasing recharge
and droughts leading to increased pumping
Evapotranspiration
Limited impact in agriculture: some crops
have higher evapotranspiration rates than
natural systems, other less
Increases as a function of temperature
increases
Water quality (in
rivers, lakes, and
aquifers)
High impact from pollution in highly
developed areas
Moderate impact through temperature
increases
Salinity in rivers
and aquifers
High impact from water withdrawal in highly
developed areas (mostly in arid regions)
Potentially high impact where sea water level
rise combines with reduced runoff and
increased withdrawal
drying in the Northern Hemisphere (Kellogg
and Zhao
1988
), while other GCM suggest that
the rise in potential evapotranspiration will
exceed that of rainfall, resulting in drier regimes
throughout the tropics and low to mid-latitudes
(Rind et al.
1990
). Because the soil moisture
processes are represented so crudely in the cur-
rent GCMs, however, it is diffi cult to associate
much certainty with these projections (IPCC
1990
).
Global climate change is likely to exacerbate
the demand for irrigation water (Adams et al.
1990
). Higher temperatures, increased evapora-
tion, and yield decreases contribute to this
projection. However, supply of needed irrigation
water under climate change is uncertain. Where
water supplies are diminishing, such as the
Ogallala Aquifer in the USA, extra demand might
require that some land be withdrawn from irriga-
tion (Rosenzweig
1990
).
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