Geoscience Reference
In-Depth Information
agricultural productivity despite overall increases in annual
water availability. Moreover, increases at peak flow will cause
damage to croplands through flooding (Gornall et al., 2010).
Globally, only a few rivers currently have adequate storage to
cope with large shifts in seasonal run-off (Barnett et al., 2005).
Where storage capacities are not sufficient, much of the winter
run-off will immediately be lost to the oceans. The water from
these glaciers feeding large rivers such as the Indus, Ganges
and Brahmaputra is likely to be contributing a significant pro-
portion of seasonal river-flow, although the exact magnitude
is unknown. Currently, nearly 500 million people are reliant
on these rivers for domestic and agricultural water resources.
Climate change may mean the Indus and Ganges become
increasingly seasonal rivers ceasing to flow during the dry sea-
son (Kehrwald et al., 2008). Combined with a rising population,
this means that water scarcity in the region would be expected
to increase in the future.
Under rising atmospheric CO
2
and climate change, the
potential impacts of devastating pathogens and insect pests
may change. This will change the crop-pest relationship
because climate (mainly temperature) plays a dominant role
in the distribution and development of pests in the following
ways: increases in the rate of development and number of gen-
erations produced per year, extension of the geographical range
beyond the present margin of distribution, earlier establishment
of pest populations in the growing season and increases in the
risk of migrant invasion and exotic species (Parry et al., 1990;
Wittwer, 1990; Rosenzweig and Hillel, 1993). A major factor in
global warming could be greater survival through over-winter-
ing and persistence of plant diseases and insects. With higher
atmospheric concentration of CO
2
, plants will grow faster and
accumulate more carbohydrates and nitrogen (Bhattacharya
and Geyer, 1993), changing the feeding habit of insects (Fajer
et al., 1989), which will lead to higher pest density and intense
damage.
An increase in the over-wintering range and population den-
sity of
Heliothis zea
in the US grain belt will increase the dam-
age to soya beans (Anonymous, 1989). Pests, such as aphids
(Newman, 2004) and weevil larvae (Staley and Johnson, 2008),
respond positively to higher CO
2
. Increased temperatures also
reduced the over-wintering mortality of aphids, enabling ear-
lier and potentially more widespread dispersion (Zhou et al.,
1995). The sub-Saharan Africa migration patterns of locusts
are influenced by rainfall patterns (Cheke and Tratalos, 2007).
Warming or drought may change the resistance of crops to
