Impacts of Climate Change on Agriculture - Climate Resilient Agriculture for Ensuring Food Security - page 69

4.6.2 Drought

which can cause yield loss if not counteracted by
irrigation.
Globally, the areas sown for the major crops
of barley, maize, rice, sorghum, soybean, and
wheat have all seen an increase in the percentage
of area affected by drought as defi ned in terms of
the Palmer Drought Severity Index (PDSI) since
the 1960s, from approximately 5-10 % to
approximately 15-25 %. The MOHC climate
model simulates the proportion of the land sur-
face under drought to have increased from 20 to
28 % over the twentieth century.
Present-day mean yield reduction rate (YRR)
values are diagnosed as ranging from 5.82 %
(rice) to 11.98 % (maize). By assuming the linear
relationship between the drought risk index and
YRR holds into the future, it is estimated that
drought-related yield reductions would increase
by more than 50 % by 2050 for the major crops.
A drought in livestock grazing systems
(Fig. 4.9 ) reduces the availability of water and
grass - both directly and indirectly because as the
watering points are reduced, some pastures are
no more accessible - and so increases the demand

Droughts have been occurring more frequently
because of global warming, and they are expected
to become more frequent and intense in Africa,
Southern Europe, the Middle East, most of the
Americas, Australia, and Southeast Asia (Fraser
et al. 2013 ). Their impacts are aggravated
because of increased water demand, population
growth, urban expansion, and environmental
protection efforts in many areas (Rosenzweig
2007 ). Droughts result in crop failures and the
loss of pasture-grazing land for livestock
(Rosenzweig 2007 ).
Droughts are damaging because of the long-
term lack of water available to the plants.
Droughts have been responsible for some of the
more serious famines in the world, although
sociological factors are also important. Heat
waves can cause extreme heat stress in crops,
which can limit yields if they occur during cer-
tain times of the plants' life cycle (pollination,
pod or fruit set). Also, heat waves can result in
wilted plants (due to elevated transpiration rates)

Fig. 4.9 Impacts of drought on livestock