Simulating the impact of extreme heat and frost events on wheat crop production: A review

Extreme weather events (frost and heat shock), already a significant challenge for grain producers, are predicted to increase under future climate scenarios. This paper reviews the current knowledge on the impacts of extreme heat (heat shock) and frost on crop production and how these impacts are incorporated into contemporary process-based crop models.Heat shock and frost result in a range of physiological impacts on wheat. Based on the literature we conclude that the greatest impacts on production from frost are associated with sterility and the abortion of formed grains around anthesis. While the greatest yield impact from heat shock are reduced grain number (sterility and abortion of grains) during anthesis to early grain filling; as well as the reduced duration of grain filling. Crop models generally did not consider the non-linear response in grain yield from a heat shock or frost event due to these key physiological impacts. While frost damage was incorporated into a number of models through winterkill functions, seedling death or advanced senescence, only the STICS model incorporated a potential decrease in grain number around anthesis. In contrast, heat shock was rarely considered within crop models, with only two examples found in the literature; (1) APSIM-Nwheat which incorporated accelerated senescence in response to extreme heat and (2) MONICA which incorporated a reduction in grain number and yield.We propose a conceptual model for the change in grain number and therefore yield in response to both a frost and heat shock event. We discuss the potential use of daily maximum/minimum temperatures, canopy temperature and heat/frost loads for determining crop response in the models. As well as identifying the need for a greater understanding on how the duration of temperature extremes impact on yield, as well as the cumulative effects of multiple heat/frost events and the interactions with other abiotic stresses including drought.