Geoscience Reference
In-Depth Information
States, Mexico, Central America, eastern Brazil and north-east-
ern and western Australia (Parry et al., 1990).
Some major rivers such as the Indus and Ganges are fed by
mountain glaciers with approximately one-sixth of the world's
population currently living in glacier-fed river basins (Stern,
2007). Populations are projected to rise significantly in major
glacier-fed river basins such as the Indo-Gangetic plain. These
river basins are irrigated agricultural land comprising less than
one-fifth of all cropped area, but produce between 40% and
45% of the world's food (Doll and Siebert, 2002). The major-
ity of observed glaciers around the globe are shrinking (Zemp
et al., 2008) due to changes in atmospheric moisture, particu-
larly in the tropics (Bates et al., 2008). Melting glaciers will
initially increase river-flow, although the seasonality of flow
will be enhanced bringing with it an increased flood risk (Juen
et al., 2007). In the long term, glacial retreat is expected to be
enhanced further, leading to an eventual decline in run-off,
although the greater time scale of this decline is uncertain. As
such, changes in remote precipitation and the magnitude and
seasonality of glacial melt waters could, therefore, potentially
impact food production for many people.
Water for irrigation is largely often extracted from rivers
such as the Nile and the Ganges, which depend upon distant
climatic conditions (Gornall et al., 2010). Agriculture along the
Nile in Egypt and in the Indo-Gangetic plains in India depends
on rainfall from the upper reaches of the Nile and the Ganges
in the Ethiopian Highlands and the Himalayas, respectively.
These areas are mostly between mid and high latitudes, where
predictions for warming are the greatest. Warming in winter
means that less precipitation falls as snow and that which accu-
mulates melts earlier in the year. The changing patterns of snow
cover fundamentally alter how such systems store and release
water. Changes in the amount of precipitation affect the volume
of run-off, particularly near the end of the winter at the onset
of snow melt. Temperature changes mostly affect the timing of
run-off with earlier peak flow in the spring. Although addi-
tional river-flow can be considered beneficial to agriculture,
this is only true if there is an ability to store run-off during
times of excess to use later in the growing season.
Thus, climate changes remote from production areas is also
critical. In rivers such as the Nile, climate change will increase
flow throughout the year that will benefit agriculture, but in
the Ganges, run-off increases in peak flow during monsoon
season while in the dry season river-flow is very low. Without
sufficient storage of peak season flow, water scarcity will affect
