By Karen Braun
FORT COLLINS, Colo., (Reuters) - La Nina conditions have started up their projected multi-month residency in the Pacific Ocean, just as new crop cycles are kicking off in the Americas, including corn and soybean planting in South America and wheat planting in the United States.
When La Nina last showed up in late 2017, it made for extremely dry growing seasons in some of these regions, particularly in Argentina and the southern U.S. Plains, and farmers harvested very poor crops in early 2018.
La Nina is characterized by cooler-than-normal surface waters in the equatorial Pacific Ocean, and this month those waters have reached the coolest levels for the time of year in nearly a decade. When the ocean cools off so much this early, La Nina typically has more staying power earlier in the next year.
Not every La Nina event has the same outcome on agriculture, but the correlation is better for some areas and crops. Argentina is the top exporter of soy products and No. 3 in corn, and the 2018 soybean harvest was more than a third lighter than normal. Corn yield was poor, but record sowings offset some losses.
Argentina’s wheat crop, in progress now, has been clipped by the persistent dryness. High soybean prices had farmers wanting to ramp up soy plantings later this year, but those plans could be derailed without a change in the weather.
Winter wheat planting has begun in the United States and while moisture has been OK for top producer Kansas, the near-term forecast is bone dry. Kansas observed record-low rainfall for much of the wheat-growing season in late 2017 and early 2018, and that dryness lingered into the summer growing season, reducing corn and soybean potential.
The U.S. Climate Prediction Center last week suggested that the last three months of the year would adopt a very La Nina-like pattern across the country. That includes dry conditions across the Southern Plains with wetter conditions in the Pacific Northwest, the former of which can be detrimental to winter wheat production.
LA NINA ARRIVES
So far in September, weekly sea surface temperature (SST) anomalies in the all-important Nino 3.4 region have averaged about 0.9 degree Celsius below normal, which would qualify as a moderately strong La Nina if it persisted for a longer period.
Since 1950, every time the SST anomaly turned similarly cool in September, a strong La Nina almost always followed, particularly in the November-January period. However, a couple of moderate La Ninas were also observed, and these milder events were also capable of destructive weather in the vulnerable regions.
If the anomaly strengthens even a little over the next month or two, that will make it much more difficult for it to fade by early 2021, which is important for the likely weather outcomes. A weaker La Nina in late 2016 faded by February 2017, and harvests in the Americas were uninterrupted.
But a moderately strong La Nina in late 2017 lingered into early 2018, introducing drought in Argentina, southern Brazil, and the U.S. Southern Plains, and associated crop losses were substantial.
Forecasters have even more confidence in the 2020-21 La Nina than they did at this point three years ago. Earlier this month, climate forecasters placed the chances of La Nina conditions during November-January at 78%, and the model-based probability is 75%.
In September 2017, prior to the last La Nina, forecasters placed those chances at 62%, and models were even more unsure at 54%. The outlooks also place higher odds of La Nina sticking around through early 2021 than they did at this point three years ago.
UNCERTAINTY IN ARGENTINA
All of Argentina’s very worst soybean and corn harvests occurred during La Nina events. Poor results were not the outcome of every La Nina, but truly good yields were very rarely observed in the midst of them. (https://tmsnrt.rs/33PVbjQ)
Forecast models show chances for some decent rain across Argentina’s parched grain belt toward this weekend. However, rain at this time of year is not necessarily an indication of things to come.
Argentine corn planting generally begins in late September and runs through January, while soy planting occurs primarily in November and December. In October 2017, grain belt soil moisture was close to an all-time high for the month after considerably above-average rainfall for much of the year.
But the situation seemed to change in an instant. In mid-to-late October 2017, it was being reported that heavy rains and wet soils were contributing to the soy planting delay. On Nov. 13, Reuters reported that dry weather was stalling the efforts, and that theme continued through the sowing period.
There was still hope when planting wrapped, but record-low rainfall in the first three months of 2018 cemented the terrible harvest results that year, negating the initially good moisture.
Argentina’s grain belt does not have a full tank of moisture heading into this season. At the end of August, soil moisture was the lightest for the date since 2009 and about 13% off the long-term average.
(Editing by Matthew Lewis)