Potential effects of increased atmospheric carbon dioxide and climate change on thermal and water regimes affecting wheat and corn production in the Great Plains

This integrative analysis of simulated wheat and corn growth in the Great Plains investigated effects of changed climatic and atmospheric conditions resulting from a doubling of atmospheric carbon dioxide (CO$\sb2$). Findings are based on global climate models (GCMs) developed by the Goddard Institute for Space Studies (GISS) and the Geophysical Fluid Dynamics Laboratory (GFDL) and the Crop Estimation through Resource and Environment Synthesis (CERES) crop models. Modifications in the crop models reflect changes in photosynthesis and stomatal resistance caused by doubled CO$\sb2$. Climate change alone reduced mean simulated dryland wheat yields by 30 and 33% in the GISS and GFDL scenarios respectively; dryland corn yields were reduced by 18 and 47%. Higher temperature was the major cause of yield reductions because shorter crop life cycles occurred with corresponding decreases in grain-fill. Changes in precipitation produced a relatively minor effect on wheat yields, but did diminish corn yields in specific locations. At many Great Plains sites, physiological effects of increased CO$\sb2$ on simulated grain growth compensated for negative impacts of climate change. However, physiological effects failed to compensate when hot, dry conditions of the GFDL scenario resulted in severe yield decreases. Simulations of climate change effects at Northern Great Plains sites indicated that winter wheat may replace spring wheat, on account of less winterkill and lower relative yield decreases. Greater warming at high latitudes, however, caused wheat yield decreases to be greater than or equal to those in the Southern Great Plains. Comparison of simulated wheat and corn responses to double-CO$\sb2$ climate change and to observed climate of the 1930s indicated that future climate may be even more detrimental to crops than that of the past. When simulations included irrigation, irrigated yields under climate change scenarios were better maintained and less variable than dryland yields. A change in planting dates in response to longer growing seasons had little effect on simulated wheat and corn yields. At certain study sites, changing cultivars did compensate for negative climate change effects. If higher temperatures predicted by GCMs occur, wheat and corn production as practiced in the Great Plains is likely to become more difficult to sustain