El Niño and La Niña Related Climate and Agricultural Impacts over the Great Plains and Midwest
Dr. Steven A. Mauget  Atmospheric Scientist USDA - Agricultural Research Service Cropping Systems Research Laboratory 3810 4th Street Lubbock, Texas 79415 806.749.5560 steven.mauget@ars.usda.gov	Dr. Dan R. Upchurch Research Leader USDA - Agricultural Research Service Cropping Systems Research Laboratory 3810 4th Street Lubbock, Texas 79415 806.749.5560 dan.upchurch@ars.usda.gov

1. )  that deterministic mechanisms exist in the Earth's climate system that are capable of shifting a region's seasonal climate from it's long term mean, and,
2. )  that these mechanisms persist or evolve predictably over inter-seasonal (i.e., season-to-season) time scales.

One mechanism that has demonstrated both the ability to produce shifts in seasonal climate over the continental U.S. and the potential for inter-seasonal predictability is the El Niño–Southern Oscillation (ENSO). Using U.S. Climate Division data, USDA-NASS yield data, and the SST Index of Wright (1989), the effects of both El Niño and La Niña Southern Oscillation phases on the central United States are evaluated, and climate and agricultural yield effects during summer and winter periods are compared. The climate analyses presented here (see Data and Methods) show that seasonal precipitation and temperature over parts of the central U.S. can be significantly skewed from climatology, conditional on the state of ENSO-associated sea-surface temperature (SST) anomalies.

• A significant tendency to cool and wet conditions over portions of the Missouri River drainage basin is found during El Niño July-August-September (JAS) periods.


• During summer periods consistent with strong La Niña conditions during JAS a significant incidence seasonal temperatures in the highest 25% of the historical record is found over Iowa, Illinois and Indiana.


• El Niño conditions during northern winter are consistent with a higher than chance incidence of wet seasonal conditions over winter wheat growing regions of Texas, Oklahoma, and Kansas.


• Conversely, La Niña winter conditions show a significant tendency to precipitation below the median and in the lowest 25% over these regions.

A general tendency for corn yields to be increased (decreased) is found after periods of warm (cold) JAS SST, and a similar effect on winter wheat yield is found after periods of warm (cold) November-December-January (NDJ) SST (see Yield Analysis and Yield Effects ). However, while significant tendencies to above or below normal yields are the rule in the winter wheat analyses, effects on corn yield – while clearly evident in some state's yield records - are less significant overall. This contrast in yield effect, combined with evidence of stronger northern winter climate impacts and the fact that the ENSO mechanism favors northern winter periods, lead us to propose (see Implications for Management) that the value of ENSO forecasts of opportunity in long-term agricultural management may be greater for winter wheat than for corn.

A related technical report in PDF form can be downloaded here: PSWCL Technical Report #2