Nonlinear heat effects on African maize as evidenced by historical yield trials

Journal name:
Nature Climate Change
Year published:
Published online

New approaches are needed to accelerate understanding of climate impacts on crop yields, particularly in tropical regions. Past studies have relied mainly on crop-simulation models1, 2 or statistical analyses based on reported harvest data3, 4, each with considerable uncertainties and limited applicability to tropical systems. However, a wealth of historical crop-trial data exists in the tropics that has been previously untapped for climate research. Using a data set of more than 20,000 historical maize trials in Africa, combined with daily weather data, we show a nonlinear relationship between warming and yields. Each degree 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 of temperate maize germplasm in other regions, and indicate the key role of moisture in maize’s ability to cope with heat. Roughly 65% of present maize-growing areas in Africa would experience yield losses for 1°C of warming under optimal rain-fed management, with 100% of areas harmed by warming under drought conditions. The results indicate that data generated by international networks of crop experimenters represent a potential boon to research aimed at quantifying climate impacts and prioritizing adaptation responses, especially in regions such as Africa that are typically thought to be data-poor.

At a glance


  1. The study region in Africa.
    Figure 1: The study region in Africa.

    The circles show locations of crop trials, with the size of the circle indicating the number of trials per site (ranging from 20 to 1,249). Weather stations with daily data for at least some portion of the study period 1999–2007 are marked as crosses. The background map shows elevation, with higher altitudes appearing darker.

  2. The effect of heat on maize yields.
    Figure 2: The effect of heat on maize yields.

    a, Regression estimates of the effects of an increase of GDD8,30 and GDD30+ by 1 degree day, using data from trials managed for optimal (n=17,713) or drought (n=3,244) conditions. Error bars indicate 95% confidence interval using robust standard errors clustered by site–year. b, Model estimate of yield impact of 1°C warming for trials at different average growing-season temperatures, using regression equations for trials with optimal or drought management. The lines are the best fits to the mean impact at each temperature level, and the shaded areas show an estimate of the 95% confidence interval using robust standard errors.

  3. Model estimates of maize yield changes for 1[thinsp][deg]C warming.
    Figure 3: Model estimates of maize yield changes for 1°C warming.

    ac, Present growing-season average temperature (a) and estimated impacts of 1°C warming for all areas for optimal (b) and drought (c) management. df, Present maize-growing area (fraction of grid cell; ref. 23; d) and estimated impacts of 1°C warming for areas with at least 1% of maize (e,f).


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Author information


  1. Department of Environmental Earth System Science and Program on Food Security and the Environment, Stanford University, Stanford, California 94305, USA

    • David B. Lobell
  2. International Maize and Wheat Improvement Center (CIMMYT), Apartado Postal 6-641, 06600 Mexico D.F., Mexico

    • Marianne Bänziger,
    • Cosmos Magorokosho &
    • Bindiganavile Vivek


D.B.L. and M.B. conceived the study, M.B., C.M. and B.V. designed and implemented crop trials, D.B.L. analysed data and drafted the paper, and M.B., C.M. and B.V. helped to interpret results and contributed to the writing.

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The authors declare no competing financial interests.

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