June 2016, Volume 6
Does El Niño’s Demise mean
a Hot, Dry Summer?
The odds of the Pacific Ocean equatorial
temperatures cooling to La Niña levels inched
higher in May. The effects of a La Niña event on
U.S. crop weather is somewhat disputed.
However, there is enough evidence, both
measured and anecdotally, to make the
assertion that La Niña is not favorable to U.S.
crop producers if it occurs during the growing
season.
When La Niña is around, especially mid- to latesummer weather conditions can turn hotter and
drier than normal. That's obviously a stressful
combination for filling corn and soybeans. U.S.
final corn and soybean yields would likely do no
better than trendline should a La Niña summer
occur.
Before La Niña becomes an issue, El
Niño needs to end and the global climate goes
through a neutral period. While IRI states that
the data is ‘noisy,’ things like 30-day and 3month averages were used. The 30-day moving
average of the Southern Oscillation Index (SOI),
which is the measure of air pressure off of Tahiti,
suggests we are moving into neutral or “La
Nada” conditions June - August.
The mid-May forecast model grouping put
together by the International Research Institute
on Climate and Society (IRI) now has a 52%
chance of the equatorial Pacific cooling to La
Niña levels (at least one-half degree Celsius
below normal) during the summer season -- the
June - August time frame.
Source: http://iri.columbia.edu/news May 22, 2016
This 52% odds of moving to a La Niña level for
July - September time frame is reflected by the
blue (dark) circle on the bar graph above. This is
a departure from the IRI’s mid-April forecast,
which had the chance of a La Niña conditions for
the June - August period had only a 31% chance
for La Niña temperatures to develop. La Niña
odds don’t increase to more than 60% until the
December - February time frame.
What happened to cause this change in the
forecast? Basically, the ocean is cooling down
more quickly than was forecast this past winter.
During early 2016, the positive tropical Pacific
Sea Surface Temperature (SST) anomaly was
quickly weakening, indicating only a weak El
Niño. The atmospheric variables continue to
support the El Niño pattern, but at much reduced
strength. This includes just mildly weakened
trade winds and excess rainfall in the central
tropical Pacific, failing to extend eastward as it
did in previous months. Most El Niño Southern
Oscillation (ENSO) prediction models indicate a
return to neutral by the end of May.
STEVEN D. JOHNSON, Ph.D.
FARM & AG BUSINESS MGT. SPECIALIST
[email protected]
515-957-5790
The IRI analysis posted on May 12, 2016,
indicates the likely development of La Niña (of
unknown strength) by the fall months.
Use of the Multivariate ENSO Index
The National Oceanic and Atmospheric
Administration (NOAA) Research Scientist Klaus
Wolter feels ENSO is the most important
coupled ocean-atmosphere phenomenon to
cause global climate variability on inter-annual
time scales. He monitors ENSO by basing the
Multivariate ENSO Index (MEI) on the six main
observed variables over the tropical Pacific.
These six variables are: sea-level pressure,
zonal and meridional components of the surface
wind, sea surface temperature, surface air
temperature, and total cloudiness fraction of the
sky.
Use of 1998 as the Analog Year
The overall evolution of the 2015-1’6 El Niño
event has been most similar to that of 1997-‘98,
as monitored by the MEI. The higher-ranked
1998 case transitioned into La Niña before the
end of that year. The summer crop weather
conditions were warm but not obsessively hot.
Timely rains fell during July and August and near
trendline U.S. yields resulted. While many
references to the 1993 adverse summer growing
conditions have been made, 1998 appears to be
the best fit for an analog year. Wolter states that
one should not discount the possibility of an
ENSO-neutral outcome this summer. The next
couple of months should still see at least weak
El Niño conditions.
Summary
When La Niña is around, mid- to late-summer
conditions can turn hotter and drier. That's
obviously a stressful combination for filling corn
and soybeans. However, research compiled at
the IRI and the NOAA indicate we are likely
moving into ENSO-neutral or “La Nada”
conditions during June - August.
Source: www.esrl.noaa.gov/psd/enso/mei June 14,
2016
The graph above features circles identifying the
top three El Niño events since 1950: 1982-‘83,
1997-‘98 and 2015-‘16. Wolter reported on June
14, 2016, that the recent nine-month run is in the
top three El Niño events. That measure was
from May-June 2015 through January-February
2016. It is tied with 1982-‘83 El Niño for its
duration, while the 1997-‘98 El Niño kept this
level going for a full 12 months.
A key feature to keep track of is soil moisture
across the Corn Belt heading into July. Most
crop areas have favorable topsoil and subsoil
moisture conditions. If these levels hold through
June, it'll go a long way toward helping crops
ward off any turn to stressful heat and lack of
rain during July and August.
No other El Niño since 1950 even exceeded
three months at that level.
STEVEN D. JOHNSON, Ph.D.
FARM & AG BUSINESS MGT. SPECIALIST
[email protected]
515-957-5790