A study done by Thornton et al. (2009) examined maize and bean crop yield response to future climate change in three distinct climates—temperate/tropical highland (MRT), humid-subhumid (MRH), and arid-semiarid (MRA). The authors focused on East African countries (i.e., Burundi, Kenya, Rwanda, Tanzania, and Uganda). The data show that in some areas of East Africa climate change will increase yield and have beneficial effects on household food security and income levels. This was primarily found in high altitude MRT areas where an increase in temperature will favor crop growth. In MRH systems, only moderate yield losses can be expected. Severe crop yield decreases are predicted for lower altitude MRA climates. These anticipated system-level shifts will take place in a context characterized by high population growth rate, and subsequent food stress. The authors suggest that adaptation to weather variation will be most successful when determined at the household and local community levels. — Anastasia Kostioukova
Thornton, P., Jones, P., Alagarswamy, G., Andersen, J., Herrero, M., 2009. Adapting to climate change: Agricultural system and household impacts in East Africa. Agricultural Systems 103, 73–82.
East Africa is climatically and topographically variable. In order to determine the response of crop yields to rising global temperatures in MRT, MRH, and MRA, the authors allocated production spatially within each country. Livestock-based systems were used due to an unavailability of sub-national crop distribution data. Further, for predicting maize and bean yields in 2030 and 2050, Thornton et al. overlaid simulated crop yields on areas where suitability had been determined for maize and bean production. The suitability factors are proper length of growing period (LGP) and suitable soil. In addition, the study incorporated four combinations of two rainfall and two greenhouse-gas emission scenarios. Since maize and beans are traditionally rainfed crops in East Africa, one drier model (HadCM3) and one wetter model (ECHam4) were used. Further, high-emission (A1FI) scenario and low-emission (B1) scenarios were used to predict future crop growth.
The study found that countries with more MRT areas are better suited for future climate change. The crops grown in these temperate, cooler climates will benefit from an increase in temperature. For example, Burundi in 2050 is predicted to have an overall crop yield increase of 9%. This is because a 9% decrease of crop yields in MRH systems will be offset by a larger 18% increase in MRT crop yield areas. Further, the authors determine that crop yield production may differ between 2030 and 2050. For example, bean production is predicted to increase in Tanzania 4% in 2030, but decrease 5% by 2050, presumably because of a temperature increase beyond maize and bean heat tolerance threshold of 20–22°C. Overall by 2050, bean and maize yields are projected to increase in Burundi, Kenya, and Rwanda, but decline in Tanzania and Uganda.
Shifting areas of farming from MRH and MRA areas to MRT systems could offset losses and be an effective response to novel temperatures in East Africa. The authors cite Kenya as an example in which crop production can increase 17% accompanying a shift from MRH to MRT farming. However, in areas with few MRT regions such as Tanzania and Uganda, shifting production may not be an option. In this case, breeding programs focused on heat-drought tolerant maize and bean varieties are a better option. Since by 2050, East Africa’s total crop yield will have a larger increase than anywhere else in Africa, a rise in regional trade could be a solution to offset yield losses and food insecurities in neighboring countries. In MRA systems, households switching to crop types such as sorghum and millet would be a good strategy to combat severe crop yield decreases by 2050. Adoption of livestock-orientated production may be another option. In addition, these anticipated system-level shifts will take place in a context characterized by a high population growth rate. Given variability in yield response and in households’ ability to adapt, investment in agricultural development will be crucial if demands are to be met in poverty alleviation and food security.