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.
Other reports in this collection