Geoscience Reference
In-Depth Information
Water is vital to plant growth, so varying precipitation pat-
terns forcing a northward advance of monsoon rainfall further
into Africa and Asia, increasing the occurrence of total rainfall,
will have a significant impact on agriculture (Parry et al., 1988,
1989; Wittwer, 1990). This rainfall will also be more intense in
its occurrence and therefore will propagate flooding and ero-
sion. Food production can also be impacted by too much water
(Gornall et al., 2010). Heavy rainfall events leading to flooding
can wipe out entire crops over wide areas and excess water can
also lead to other impacts, including soil water logging, anaer-
obicity and reduced plant growth. Indirect impacts include
delayed farming operations. Agricultural machinery may not
be adapted to wet soil conditions. The proportion of total rain
falling in heavy rainfall events appears to be increasing and
this trend is expected to continue as the climate continues to
warm. A doubling of CO
2
is projected to lead to an increase in
intense rainfall over much of Europe. In the higher end projec-
tions, rainfall intensity increases by over 25% in many areas
important for agriculture. As over 80% of total agriculture is
rain-fed, projections of future precipitation changes often influ-
ence the magnitude and direction of climate impacts on crop
production (Olesen and Bindi, 2002; Tubiello et al., 2002). The
impact of global warming on regional precipitation is difficult
to predict owing to strong dependencies on changes in atmo-
spheric circulation, although there is growing confidence in
projections of a general increase in high-latitude precipitation,
especially in winter and an overall decrease in many parts of
the tropics and sub-tropics (Anonymous, 2007b).
Precipitation is not the only influence on water availability.
Increasing evaporative demands owing to rising temperatures
and longer growing seasons could increase crop irrigation
requirements globally by between 5% and 20% or possibly
more by the 2070s or 2080s, but with large regional variations,
increasing in the Middle East and North Africa and South-East
Asia (Doll, 2002; Abou-Hadid et al., 2003; Arnell et al., 2004;
Fischer et al., 2006) and decreasing in China (Tao et al., 2003).
The temperature increase due to elevated CO
2
will also induce
higher rates of evapotranspiration causing reduction in soil mois-
ture (Schlesinger and Mitchell, 1985; Kellogg and Zhao, 1988;
Zhao and Kellogg, 1988; Parry et al., 1990). The areas which
may suffer due to reduced soil moisture between December and
February are southern and western Africa, South-East Asia,
the Arabian peninsula, eastern Australia and southern North
America, while between June and August are West Africa,
western Europe, China, Soviet Central Asia, South-West United
