Effects of changes in minimum and maximum temperature on wheat yields in the central US - A simulation study

Recent observations and general circulation models indicate that future temperature changes linked to global warming might be characterized by a marked asymmetry between daytime maxima and nighttime minima. We investigate the importance of such a pattern in determining future wheat (Triticum aestivum) yields in the Central United States by using a dynamic crop growth model, CERES-Wheat, modified to include physiological effects of temperature and CO2 on canopy photosynthesis. Simulations are run at four sites spanning a north-south transect of the Central US; four mean temperatures increases (1-4 degrees C) are applied to baseline daily climate data (1951-1980). The effects of two different scenarios of temperature change (minimum and maximum temperatures equally raised; minima increased three times as much as maxima in agreement with recent observations) are analyzed under both current (330 ppm) and elevated (550 ppm) CO2 concentrations. The main mechanisms controlling the simulated wheat responses are direct and indirect temperature effects on wheat phenological development. Negative effects of temperature on simulated wheat yields are reduced when minima increase more than maxima. Yield changes are consistently negative under temperature change and current CO2 concentration, while they range from positive to negative under temperature change and elevated CO2 concentration. Responses vary across the transect, with larger negative effects occurring at the southernmost site.