Modelled wheat phenology captures rising temperature trends: Shortened time to flowering and maturity in Australia and Argentina

Phenological development is the most important attribute of crop adaptation and long-term changes in phenology provide strong evidence of the biological impact of warmer climates. This paper takes the documented increase in temperature during the last decades as a starting point, and quantifies the changes in wheat phenology in (a) 53 locations in eastern Australia between 1957 and 2000 using the APSIM model, and (b) 17 locations in the Pampas between 1971 and 2000, using CERES-Wheat. The expectation is shortened season length associated with warmer climate; the aim is to quantify the actual magnitude of phenological changes, the relative changes in the duration of pre- and post-flowering phases, and the interaction between changing temperature and sowing date.Modelled time from sowing to maturity was reduced up to ∼0.3 d y−1; time to flowering accounted for most of the variation in time to maturity. The rate of change in the duration of modelled wheat phenophases was more marked with early sowing. Owing to the cumulative effect of temperature on crop development assumed in the models, significant changes in rate of development were detected in some cases when change in temperature was statistically undetected. A minimum rate of mean temperature increase ∼0.02 °C y−1 was required for significant shortening of time to flowering and season length. In agreement with rates derived from field experiments, the rate of change in modelled time to flowering and maturity was ≈7 d °C−1. The duration of the post-flowering phase was largely unchanged. This was associated with lack of change in temperature, or where temperature increased, earlier flowering that shifted post-flowering development to relatively cooler conditions, thus neutralising the trend of increasing temperature.