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Nonlinear Heat Effects on African Maize as Evidenced by Historical Yield Trials

Development Challenge

As the impacts of climate change accelerate around the globe, policymakers must anticipate major changes in food systems. New approaches are needed to understand how rising temperatures will impact crop yields, particularly in tropical regions. Effective adaptation of agriculture to climate change in the developing world will require both a deep understanding of the risks faced by different locations as well as the causes of potential damage. Many approaches to gather this critical information are limited, especially in developing countries. For example, simulation models function on imperfect information about agricultural inputs, and statistical approaches are frequently limited by the quantity and quality of data, which results in fairly large uncertainties.

Context

The International Maize and Wheat Improvement Center (CIMMYT), National Agricultural Research Programs and private seed companies manage research stations throughout Africa. One set of trials run by these groups focused on tropical maize and was originally intended to test new varieties across a range of environmental conditions to find the most robust lines. The varieties included in this dataset were grown or intended for farmers’ fields throughout Africa, nearly all of which are rain-fed. The large size of this data set enabled the research team to offer more precision than previous empirical studies on the impacts of climate change on crop yields.

Evaluation Strategy

The research team relied on data from more than 20,000 field trials conducted between 1999 and 2007 on a network of 123 research stations. Each combination of maize variety, station, year and management regime counted as a single trial. For each of these trials, the team recreated the daily temperature and precipitation using thin-plate spline interpolation that used data recorded daily at nearby weather stations. The researchers then computed various summary statistics of the growing season weather, including average temperatures for critical development phases and time spent above critical temperature thresholds, in order to map potential impacts for maize under optimal or drought conditions across sub-Saharan Africa.

Results and Policy Implications

Overall, the study results show two important conclusions. First, maize yields in Africa may increase from warming at relatively cool sites, but fall significantly in areas where temperatures commonly exceed 30°C. Second, sensitivity to heat is clearly exacerbated in drought conditions. Each day spent above 30°C reduced the final yield by 1% under optimal rain-fed conditions, and by 1.7% under drought conditions. These results are consistent with studies on maize in other regions, and indicate the key role of moisture in enabling maize to cope with heat. Looking at the continent as a whole, roughly 65% of present maize-growing areas in Africa would experience yield losses for 1°C of warming under optimal conditions and 100% of areas would be harmed by warming under drought conditions. These results indicate that data generated by crop experimenters are a potential boon to research aimed at quantifying climate change impacts. This research will facilitate better understanding and enable prioritization of adaptation measures in some of the most vulnerable regions of the world.

Photo Credit: IITA, 2009.