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Heat, Drought and Europe’s Maize
What 15 harvests in 132 regions say about a hot or dry summer
Maize statistics © European Union, Eurostat. Weather: E-OBS v33.0e (ECA&D and the Copernicus Climate Change Service), for non-commercial research and education. Regional boundaries © EuroGeographics for the administrative boundaries, from GISCO, for non-commercial use. Crop calendar: GGCMI, and map of maize: MIRCA-OS, both under a Creative Commons Attribution licence (details below).
Grain maize is one of the European Union’s main cereals, and unlike wheat it grows through the hottest weeks of the summer. A companion study of wheat, with a similar design, found no established effect of heat or drought on wheat yields once its flawed drought test was corrected. This piece asks the same questions of maize. The design was registered before any maize yield was looked at, and every number below is read by code from the result files in the project repository.
In short: by the study’s rules, a dry season lowers maize yields, and that result survives leaving out any single country except Spain. Heat probably lowers them too, but it only just clears the bar the study set itself, and much of its estimate comes from one country. A second analysis, registered after a critical review, measures the weather where maize grows and removes more flawed figures: both results hold there, heat a little more clearly, though it is smaller without Romania.
