SENSITIVITY OF CROP YIELD AND WATER-USE TO CHANGE IN A RANGE OF CLIMATIC FACTORS AND CO2 CONCENTRATIONS - A SIMULATION STUDY APPLYING EPIC TO THE CENTRAL USA

Crop production was simulated with the Erosion Productivity Impact Cal culator (EPIC) for five representative farms in the Midwestern USA und er a variety of climate scenarios. The impact on yields and water use in corn, soybean, winter wheat and sorghum was simulated over a range of temperature, precipitation, solar radiation, humidity and atmospher ic carbon dioxide concentration ([CO2]) conditions. Stomatal resistanc e and leaf area index, plant physiological factors affected by changes in [CO2], were also varied in some of the simulations. Changes in eac h of these variables altered crop yields and water use. Increases in t emperature accelerated the phenological development for all crops, sho rtened time to maturity, lowered yields, and decreased water use effic iency. Changes in precipitation and vapor pressure affected crop yield and water use by altering the degree of water stress experienced by t he crop. For all crops, changes in precipitation and vapor pressure we re positively correlated with changes in yield. Changes in solar radia tion, which affect the amount of photosynthetically active radiation c aptured by the plant, were positively correlated with changes in crop yield. Increases in [CO2] and consequent increases in leaf area index and stomatal resistance increased crop yield and water use efficiency, lessening any negative impacts of changes in temperature, precipitati on, vapor pressure and solar radiation and amplifying their positive e ffects. Interactions between different climate variables resulted in c rop yield responses ranging from a multiplicative decrease when humidi ty and precipitation are decreased to a reduction in crop yield when s olar radiation is increased and precipitation decreased. The demonstra ted interactions of climatic factors indicate that future studies of c limate change impacts should consider the full spectrum of climate var iables and changes in atmospheric CO2 and not just temperature and pre cipitation.