SENSITIVITY OF THE US CORN-BELT TO CLIMATE-CHANGE AND ELEVATED CO2 .1. CORN AND SOYBEAN YIELDS

Climate models indicate that increasing atmospheric concentrations of CO2 and other greenhouse gases could alter climate globally. The EPIC (Erosion Productivity Impact Calculator) model was used to examine the sensitivity of corn and soybean yields over the US corn belt to chang es in temperature, precipitation, wind and atmospheric CO2 concentrati on. A statistically representative sample of 100 corn and soybean prod uction sites was selected from the 1987 National Resources Inventory ( NRI). One-hundred-year simulations were run for each site under 36 dif ferent climate/CO2 scenarios. The results were area weighted according to the NRI area expansion factor's to produce a regionally aggregated estimate of yields. EPIC did an excellent job of reproducing current regional mean expected yields under the baseline scenario. There were 3% decreases in both corn and soybean yields in response to a 2 degree s C temperature increase at baseline precipitation levels, with larger and smaller temperature effects under drier and wetter conditions, re spectively. Crop yields increased and decreased in response to increas es and decreases of 10% or 20% precipitation. A 10% precipitation incr ease roughly balanced the negative effect of the 2 degrees C temperatu re increase. Whether the precipitation changes resulted from altered p recipitation event frequency or amount per event had little effect on mean crop yields; however interannual yield variability was higher whe n precipitation decreases were due to frequency rather than intensity. The opposite was true, though to a lesser extent, far precipitation i ncreases. Potential evapotranspiration responded linearly to changes i n mean wind speed, leading to modest changes of 1-3 days of water stre ss per growing season, yield increases of up to 2% for decreased wind, and yield decreases of up to 6% for increased wind. Elevated CO2 conc entrations of 625 ppmv gave the greatest yield increases, +17% for cor n and +27% for soybean at baseline temperature and precipitation level s. The relative CO2 effect was larger under drier conditions. Copyrigh t (C) 1996 Published by Elsevier Science Ltd