by David Widmar
One of the biggest stories of the summer was the strong El Nino conditions. By several measures, current conditions are among the strongest El Nino measurements in history (Secord or third highest since 1950). Recent media articles have also citied El Nino related agricultural production issues to higher dairy, sugar, palm oil, and wheat prices. It appears, however, that the most significant impact will occur this winter.
This got us wondering how current El Nino conditions might impact the winter wheat crop. Similar to our post earlier this summer, which considered corn and soybean yields, this week we take a look at historic El Nino conditions to glean potential insights for the US winter wheat crop.
El Nino and U.S. Yields
By considering the Oceanic Nino Index (ONI) the fall prior to harvest, or when winter wheat is planted, we considered if warm ONI values (or El Nino favoring conditions) or cool index values (or a La Nina favoring event) result in a higher likelihood of above trend yields.
From 1951 to 2014, there were a total of 40 warm/cool ONI events during these fall months. These were equally split between El Nino (warm) and La Nina (cool) conditions. In figure 1, the relationship between the ONI values and wheat yields are presented. The bars represent the difference between the annual trend adjusted yield and the U.S. average trend-adjusted yield. The shading of the bar corresponds to the observed ONI conditions for the growing season (red for warm, blue for cool, black for neither) .
In years where yields have been well above trend, both El Nino and La Nina have been experienced. The highest above-trend yield (+6.5 bushel in 1983) corresponded with El Nino conditions in the previous fall. Overall, the eight highest above-trend yields observed since 1950 occurred during an El Nino or La Nina conditions in the previous fall; 4 El Nino and 4 La Nina.
At the national level El Nino and La Nino conditions both resulted in above-trend yields an equal number of times, or 45% of the time. Furthermore, over the 64 years of data above-trend yields overall were experienced 42% of the time. This is to say that across that across the country, El Nino events have historically resulted in above- (and below-) trend yields at nearly the same frequency as average. The same is true for La Nina.
Figure 1. Departure of Trend-Adjusted Wheat Yields from Average (1951-2014) and ONI Conditions for the Fall (Warm, El Nino favoring in red; Cool, La Nina favoring in blue; Neutral in black). Data Sources: USDA NASS, National Weather Service’s Climate Prediction Center.
While above trend-yields do not occur more frequently during fall El Nino conditions at the national level, there is substantial variation at the state-level. Shown in figure 2 is the share of historic fall El Nino conditions that resulted in above-trend state-level yields.
Across the Plains states, the historic probability of above-trend yields during El Nino conditions were high, 65% or greater. This was especially true in the Southern Plains states of Kansas, Oklahoma, and Texas, which accounted for 49% of the winter wheat planted in 2014. Texas, for instance, has historically experienced above-trend yields 70% of the time fall El Nino conditions were present .
In Kansas, the largest producer of winter wheat by planted acres (2014), years where El Nino conditions have occurred during the fall months has resulted in yields as high as nearly 12 bushel above trend to as low as 10 bushel below trend (not shown). Quite a range of potential outcomes. Overall, El Nino conditions have resulted in above trend yields 65% of the time.
Figure 2. Percent of Times Yields were Above Trend Average in El Nino Conditions, by State. Data Soucres: USDA NASS, National Weather Service’s Climate Prediction Center.
Wrapping it Up
From a historic perspective, El Nino conditions in the fall have resulted in above-trend yields 45% of the time; nearly the same frequencies over 64 years of total yield data and La Nina conditions. There is no historic pattern of above- (or below-) trend yields occurring more frequently during fall El Nino conditions.
It is noteworthy, however, the eight highest above-trend years occurred during both El Nino and La Nina years. This would suggest that if a bin-busting winter wheat crop were to happen, El Nino or La Nina conditions would like be present in during the fall growing conditions.
Finally, at the state-level the impacts can vary. Texas, for instance, has experienced above-trend yields during 70% of past fall El Nino events.
Photo Source: Flickr/J. Triepke
 For this analysis the fall 3-month periods of September-October-November, October-November-December, and November-December-January where considered. To be considered El Nino (La Nina) favoring, the three periods must have all been consistently warm (cool). For a period to be warm or cool, 5 consecutive observations of the 3-month running average more than (less than) 0.5 degrees Celsius above (below) normal conditions are prime for an El Nino (La Nina).
 It should be noted that most state have reported winter wheat yields for all 20 observed fall El Nino events since 1950. Given the small number of observations, each observations is equal to 5% points and can move significantly. At the national-level, yields were above-trend 9 out of 20 times fall El Nino conditions were present. In Kansas, for instance, above-trend yields occurred 13 out of 20 times