Submitted to: Agricultural and Forest Meteorology Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: August 15, 1998
Publication Date: N/A
Interpretive Summary: Climate uncertainties make the year-to-year practice of farming similar to an ongoing game of chance. Before planting, the farmer decides what and how much to grow, and then gambles on whether climate conditions during the growing season will allow his management decisions to "pay off". Predicting seasonal growing conditions before planting might be compared to "loading the dice" in the farmer's favor. However, seasonal climate prediction requires climate mechanisms that actually behave predictably over season- to-season time scales. The El Nino-Southern Oscillation (ENSO) mechanism has shown evidence of such behavior, and can significantly affect climate over the United States. Using U.S. Climate Division data, USDA yield data, and eastern Pacific sea-surface temperature data, the effects of both the El Nino and La Nina ENSO phases on the central U.S. were evaluated. Our emphasis was on comparing climate and agricultural yield effects during summer and winter periods. Results found here show significant climate effects during both summer and winter, and significant yield effects on corn and winter wheat crops. Generally speaking, per-acre corn and winter wheat yields tend to be increased after growing periods marked by El Nino conditions, and reduced after growing periods consistent with La Nina conditions. However, while significant tendencies to above or below normal winter wheat yields are the rule, effects on corn yield are less signifi- cant overall. This contrast in yield effect, together with evidence of stronger northern winter cimate impacts and the fact that the ENSO mechanism favors the northern winter months, lead us to propose that the value of ENSO forecasts in long-term agricultural management may be greater for winter wheat than for corn.
Technical Abstract: Seasonal climate prediction requires climate mechanisms that behave predictably over season-to-season time scales. One mechanism that shows evidence of such behavior is the El Nino-Southern Oscillation (ENSO). Using U.S. Climate Division data, USDA-NASS yield data, and the Wright's (1989) sea-surface temperature (SST) index, the effects of both El Nino and dLa Nina Southern Oscillation phases on the central U.S. were evaluated, an climate and agricultural yield effects during summer and winter periods are compared. Results presented here show a significant tendency to cool and wet conditions over parts of the Missouri River drainage basin during El Nino July-August-September (JAS) periods. During JAS periods marked by strong La Nina conditions a significant incidence of 4th quartile seasonal temperature is found over Iowa, Illinois and Indiana. While El Nino winters are consistent with an increased incidence of wet seasonal conditions over winter wheat growing regions, La Nina conditions show a significant tendency to below median and 1st quartile precipitation. 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. But, while significant tendencies to above or below normal yields are the rule in the winter wheat analyses, effects on corn yield 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 that the value of ENSO fore- casts of opportunity in long-term agricultural management may be greater for winter wheat than for corn.