The role of ENSO in determining climate and maize yield variability in theUS cornbelt

Recent advances in understanding the role of the El Nino- Southern Oscillat ion (ENSO) in climate variability present opportunities for improving effic iency in agricultural production. We investigated the relationships between ENSO, climate and maize yields in the U.S. cornbelt, using both observed d ata and crop simulations. Using a time-series of sea-surface temperature an omalies (SSTA) from the NINO3 region of the Pacific Ocean and historical re cords of temperature and precipitation spatially averaged across 51 mid-wes tern climate divisions from 1950 to 1995, we ran linear correlation tests a t three different lags. Northern hemisphere wintertime SSTAs were significa ntly correlated with air temperature at the 95% level of confidence in both the previous (r = -0.32) and following (r = 0.41) summer, but had opposite signs. Correlations with precipitation were significant only in the summer preceding the ENSO event (r = 0.31). Detrended maize yield for the same ar ea and time period was also significantly related to SSTAs in the winter af ter harvest, with a correlation coefficient of 0.39, indicating that ENSO a ccounts for approximate to 15% of interannual maize yield variability in th e cornbelt. Crop growth simulations at seven sites across the region sugges t that water stress in July and August is the primary cause of lowered corn yield in La Nina years, but shortened grainfill period due to higher tempe ratures is also important. The benefits of El Nino-related rainfall and coo ler temperatures are less pronounced than the negative impacts of warmer an d dryer La Ninas. However, advance warning of both ENSO phases may present opportunities for improved crop management in the cornbelt. Copyright (C) 1 999 Royal Meteorological Society.