Wheat yield loss attributable to heat waves, drought and water excess at the global, national and subnational scales
Heat waves and drought are often considered the most damaging climatic stressors for wheat. In
this study, we characterize and attribute the effects of these climate extremes on wheat yield
anomalies (at global and national scales) from 1980 to 2010. Using a combination of up-to-date
heat wave and drought indexes (the latter capturing both excessively dry and wet conditions), we
have developed a composite indicator that is able to capture the spatio-temporal characteristics of
the underlying physical processes in the different agro-climatic regions of the world. At the global
level, our diagnostic explains a significant portion (more than 40%) of the inter-annual
production variability. By quantifying the contribution of national yield anomalies to global
fluctuations, we have found that just two concurrent yield anomalies affecting the larger
producers of the world could be responsible for more than half of the global annual fluctuations.
The relative importance of heat stress and drought in determining the yield anomalies depends
on the region. Moreover, in contrast to common perception, water excess affects wheat
production more than drought in several countries. We have also performed the same analysis at
the subnational level for France, which is the largest wheat producer of the European Union, and
home to a range of climatic zones. Large subnational variability of inter-annual wheat yield is
mostly captured by the heat and water stress indicators, consistently with the country-level result
