In Egypt, Eid (1994) evaluated wheat and maize sensitivity to warmer temperatures;
Strzepek et al. (1995; see also Conway and Hulme, 1996) reported an integrated
assessment of climate change impacts on coastal resources, agriculture, and
water. The agricultural sector is highly sensitive to climate change, although
different scenarios result in widely different impacts on irrigated agriculture.
In Kenya, a recent study by the International Institute for Applied Systems
Analysis (IIASA) (Fischer and van Velthuizen, 1996) highlights the diverse effects
of climate change. The Food and Agriculture Organization (FAO) Agroecological
Zone model was used to delineate crop-growing regions and their suitability
for a wide range of crops. Rising temperatures and increased plant water requirements
would lead to dramatic reductions in agricultural production potential, especially
in eastern and southern Kenya. In central and western Kenya, temperature increases
would result in an extension of the land suitable for cultivation because some
higher-elevation areas would become suitable for cropping. Along with higher
cropping intensities in the highlands, this effect more than outweighs the effects
of moisture stress in the lowlands. In humid regions (>270 days of growing periods),
diminished wetness could reduce pest and disease constraints. The balance of
increased evapotranspiration and precipitation in semi-arid regions determines
the effect of climate change on agriculture and food security in the lowlands.
Using the ACRU/CERES hybrid model-one of the most sophisticated crop-climate
models developed in Africa-Schulze et al. (1996) have evaluated the impact of
climate change on maize in South Africa. The investigators divided the diverse
geography of South Africa into 712 relatively homogeneous zones, each associated
with vegetation, soil, and climate data. Daily values of temperature (minimum
and maximum), rainfall, wind speed, and solar radiation are used in the crop
evaluation, based on the CERES-Maize model. Recent scenario analysis of the
model (see Hulme, 1996a) shows a wide range of potential maize yields in South
Africa. For three scenarios of climate change (corresponding to the middle of
the next century), yields decrease in the semi-arid west. For most of the country,
however, potential yields would increase-generally by as much as 5 t/ha. The
CO2 enrichment effect counteracts the relatively modest changes in temperature
and precipitation. In parts of the eastern highlands, particularly in Lesotho,
dramatic increases in yields result from higher temperatures.
Hulme (1996b) presents an integrated view of climate impacts in southern Africa.
Prospects for agriculture depend critically upon changes in precipitation. A
"dry" scenario suggests less-suitable conditions in semi-arid and subhumid regions.
With little decrease (or increases) in precipitation, agriculture should be
able to cope with the average changes. However, shifts in drought risk need
to be considered.
Ultimately, climate change is a global issue-even more so for traded commodities
such as agricultural products. Some regions, for example, may be less competitive
in national and global agricultural markets, with corresponding impacts on exports
and imports. Africa, in particular, may be sensitive to changes in world prices
and stocks because many countries rely on food imports. Several world-trade
models have been tested with scenarios of climate change, with differing assumptions
regarding economic growth, population growth, trade liberalization, and technological
innovation (see Fischer et al., 1994, 1996; Rosenzweig and Parry, 1994). Because
they are global simulations, they can illustrate some of the dynamic adjustments
in world prices and regional imports and exports that may result from climate
change. However, Africa is not well represented in such assessments. Scenarios
tend to be trend projections that discount the potential for dramatic improvements
in agriculture or welfare. Moreover, the lack of uniform and accessible data
on crop-climate sensitivity in Africa leads to large uncertainties in predicted
impacts in Africa. A critical question is the extent to which climate change
at the global level alters African exports (reflecting changes in comparative
advantage) and food imports (reflecting the world price of cereals).
Most livestock in Africa are herded in nomadic areas, although significant
numbers are kept in paddocks on farms. Domestic animals, especially cattle,
also will be affected by climate change. In the cold highlands of Lesotho, for
example, animals would benefit from warmer winters but could be negatively affected
by a lowering of the already low nutritional quality of grazing. Heat stress
also is a concern in warmer areas. The direct impacts of changes in the frequency,
quantity, and intensity of precipitation and water availability on domestic
animals are uncertain. However, increased droughts could seriously impact the
availability of food and water-as in southern Africa during the droughts of
the 1980s and 1990s (IPCC, 1996).
Agricultural pests, diseases, and weeds also will be affected by climate change.
Little quantitative research on these topics has been undertaken in Africa,
however. Perhaps the most significant shifts could occur in tsetse fly distributions
and human disease vectors (such as mosquito-borne malaria). Tsetse fly infestation
often limits where livestock can be kept or the expansion of extensive agriculture
(Hulme, 1996a). Declining human health would affect labor productivity in agriculture.
African economies depend on natural resources, and the impact of changing natural
resources affects several sectors. Perhaps more so than in many regions, the
cross-sectoral impacts of climate change need to be understood. Agriculture
depends on water resources, a healthy labor supply, and demand for its products.
In turn, rural health, incomes, and development depend on viable agricultural
economies. One example of the potential interactions is the role of drought.
A small change in drought risk need not affect agriculture to a great extent,
as long as food supplies and household income can be saved over several years.
However, an increase in drought risk could affect regional water supplies, leading
to rationing of water and energy and reduced irrigation. Increasing aridity
and prolonged spells of severe drought could accelerate abandonment of the rural
economy and migration to urban centers.