An extract from 2017 African Transformation Report
As the effects of climate change build, humid and sub-humid areas in Sub-Saharan Africa are expected to receive higher rainfall, while the drier areas are likely to experience less—
and more erratic—rainfall. A simulation using a set of 21 global models showed that East Africa will experience a 7% increase in precipitation in 2080–2099 relative to 1980–1999. The increase will be more evident around the Lake Victoria basin. West Africa’s humid and subhumid zones will see a 2% increase in precipitation, while the Sahara subregion will see a 6% drop. New opportunities could open up for farmers in the areas experiencing an increase in precipitation, allowing them to produce crops that would otherwise be impossible to grow.
Temperature is expected to increase across Africa, which could undermine the positive effects of increased precipitation by accelerating evaporation in East Africa and parts of West Africa. While higher temperatures are generally expected to lower productivity by reducing soil water content, they may benefit farming at higher altitudes by prolonging the growing season, reducing the amount of time needed for crops to mature, increasing the survival rate of young animals, and generally raising livestock productivity.
Cereal crops are a key to adapting to climate change because the increased carbon in the atmosphere will improve their productivity (enhanced photosynthesis due to higher levels of carbon in the atmosphere, known as carbon fertilization), although higher temperatures and greater variation in rainfall are expected to outweigh the positive impact of carbon fertilization in some parts of the world. By 2080, a consensus estimate of six climate models and two crop modeling methods—assuming a 4.4°C increase in temperature and a 2.9% increase in precipitation—finds that global agricultural output potential is likely to fall by about 6%, or by about 16% without factoring in the positive effect of improved photosynthesis from increased carbon in the atmosphere. The potential agricultural output decline ranges from 10% to 25% among the world’s regions.
By 2080 across Africa, as climate change progresses, cereal output potential could fall by 16%–27% on average and by up to 60% in some countries, depending on the effect of carbon fertilization. These effects are in addition to general water scarcity and changes in rainfall patterns.
The following assessment considers mainly the direct impacts of climate change on the four determinants of productivity just discussed, not the indirect effects such as disturbance of natural selection, which require more sophisticated modeling that is beyond the scope of this chapter.
Application of fertilizer. If water shortages intensify, that could undermine the effectiveness of fertilizer application. An experiment on maize in Niger found that the grain yield response to nitrogen differed with the level of the water deficit and with the level of nitrogen application. Under conditions of water shortage (low rainfall), yield reductions were much more severe at high nitrogen rates. This implies that areas where climate change causes a decline in precipitation will experience a greater reduction in fertilizer effectiveness, holding everything else constant. In addition, if fertilizer is not applied at the right time, increases in rainfall could also reduce the effectiveness of fertilizers by washing them off the soil before they have a chance to nourish plants. And because fertilizer requires the correct amount of water at the right time to work effectively, temperature increases will also reduce the effectiveness of fertilizers by increasing the evaporation rate. For carbon-4 crops, however, which will be affected by countervailing forces, it is difficult to draw any conclusions about the impact of temperature change on fertilizer effectiveness.
Irrigation infrastructure. Official records for irrigated areas in Sub-Saharan Africa show that full-control surface water irrigation accounts for more than half of the total irrigated area of 7.1 million hectares,including mainly publicly funded irrigation schemes.
Performance of these irrigation systems is poor, as 20% of the developed area is no longer cultivated.29 Irrigation’s contribution to raising productivity in Sub-Saharan Africa is expected to decline with the anticipated reduction in annual rainfall.
The effectiveness of irrigation under climate change is likely to vary across African subregions. Irrigation effectiveness is expected to be enhanced in East Africa and parts of Central Africa and in the humid and subhumid zones of West Africa, but reduced in Southern African because of diminished rainfall. However, the overall effectiveness of irrigation may be weakened by a higher rate of water evaporation, especially for open furrow irrigation, as a result of expected higher temperatures across the continent.
Adoption of improved seeds. The impact of climate change on improved seeds is ambiguous. Seeds are constantly being improved to increase crop resilience to shocks associated with climate change, such as water stress and temperature change. Nonetheless, if climate change effects are severe enough, they may undermine the effectiveness of drought-resistant seeds. Improved seeds that strengthen crop tolerance to flooding appear to be less needed. While such tolerance could be useful in places where flooding is likely, it would be useless everywhere else, as this type of seed would not be suitable for areas that do not flood or are far from water.
Mechanization. Dry conditions caused by both water shortages and higher temperatures (evaporation) can make plowing more difficult. Plowing may therefore require more machine effort, which would raise the cost of mechanization. For farmers who can already barely afford to mechanize, higher costs would mean forgoing or limiting the use of machinery for plowing and increasing the use of hand hoes. A hand hoe does not lead to the land-degrading soil disturbance and compaction experienced in highly mechanized farming, but by increasing the drudgery and the need for labor, it could constrain farmers’ adoption of some land management practices that lead to higher yields and adaptation to climate change.
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