Death comes to us all. Life's but a walking shadow | I took some time to extend your analysis of the potential for adverse crop weather using the NOAA data you referenced in a post below that you may find interesting. I took the data from their table of monthly ONI (Ocean Nino index) data since 1950 (that you pointed out), reorganized it so that it could be plotted in a continous fashion and compared it with US corn yields. Since corn yields increase systematically I calculated a trendline without any correction and then calculated the difference between the reported yield and the expected trend yield value then plotted this difference (or residual) against the ONI. The blue line in the chart is the monthly ONI starting in Jan 1950 to present while the red line is the difference between the annual reported yield and the expected trend value. Due to my plotting program I couldn't easily label the years but it isn't hard to pick out the important ones. Also, please note that the red horizontal dashed line is the zero line of the yield residual chart.
Careful inspection of the chart indicates that with the exception of a couple of years almost anytime the ONI exceeds +1 (the blue horizontal line) the following crop year yield is depressed. The most glaring exception is 2012. There despite the decline in ONI a severe drought occurred. Additional inspection seems to indicate that even in years when the ONI doesn't exceed +1 the follow year crop yield declines. There also seems to be a connection between how long the ONI stays elevated and a decline in yield. This makes intuitive sense. The lack of rain in the previous fall very well may influence the subsequent season.
It is important to keep in mind a couple of points. First, the climate prediction team indicates that the ONI can fluxuate rapidly even month to month as well as uncertainty in the data. Averages like those used here might miss important events. Second, I've made no correction in the trendline for all the other agronomic factors that may affect yield, unstable varieties, other weather factors (like the Atlantic Occillation) etc.
I think the important point to take from this chart is the fact that the current ONI is well above +1. In another few months, possibly before planting next spring we'll have more data to examine.
I think the results suggest that if it is possible it may be advantageous to store at least some of this year's crop. Of course if the ONI collapses next month you lose that advantage.
It's important to point out that by not correcting the yield trendline I've allowed the few very poor yields to lower the expected yields and skewed the residuals slightly lower. By doing so I have possibly reduced the strength of the correlation between the ONI and yield residuals.
Edited by 1234 11/15/2015 08:45
 (yld 50- 15-page-001.jpg)
 (ONI vs yield residual-page-001.jpg)
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 yld 50- 15-page-001.jpg (71KB - 139 downloads)
ONI vs yield residual-page-001.jpg (124KB - 130 downloads)
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JonSCKs, El Nino
