Senwes Scenario December 2018 / January 2019 | Page 34

GRAIN BROKERS
El Niño
El Niño – What is expected and what can we learn from previous seasons?
El Niño has become a general point of discussion when price formation expectations are
raised going into the new season.
 By Frans Dreyer
Manager: Senwes Grain Brokerage
T
he probability of an El Niño
event is currently (beginning of
November 2018) estimated at at
least 70% from November 2018
to March 2019. The first concern amongst
most roleplayers is the impact which the
event had on rainfall and the poor yields
during the 2015/2016 season.
This potential reality forced us to
evaluate the ENSO (El Niño Southern
Oscillation) phenomenon in perspective
by looking at the impact thereof on the
central and western production area. As
part of the discussion it would be sensible
to relook at the basic background to such
a phenomenon and how it is determined.
This article accordingly focuses on the
background which will form the basis for
follow-up articles regarding the intensity
of the ENSO-phenomenon and the impact
thereof on the central and western pro-
duction area.
El Niño and La Niña phenomena
are global weather phenomena. They
originate in the Pacific Ocean when the
atmospheric pressure between the island
of Tahiti and Darwin (Northern Australia)
varies. The measurement of the difference
32
in atmospheric pressure between the two
points of reference is done by means of
the SOI (Southern Oscillation Index). The
difference in atmospheric pressure results
in trade winds which normally blow from
the east to the west across the Pacific
Ocean, no longer following this pattern.
During an El Niño-event the atmospheric
pressure changes to the extent where
trade winds weaken or even change
direction, which results in warmer than
normal sea surface temperatures over
the central and eastern tropical Pacific
Ocean.
This phenomenon goes hand in hand
with an increased chance of below normal
rainfall over the western areas of South
Africa and particularly the inland areas of
Eastern Australia. However, the opposite
phenomenon, namely La Niña, goes hand
in hand with above average strong trade
winds which cause warmer than normal
sea surface temperatures over the north-
ern areas of Australia, with an increased
chance of above normal rainfall over
Australia and South Africa.
Research over time has developed
to the extent where various models can
be implemented to determine the prob-
ability of either an El Niño or La Niña
phnomenon. The first indication of the
development of the phenomena is usually
SENWES SCENARIO | TECHNOLOGY & INNOVATION 2018
the changed SOI-values. Should the SOI
values be higher than +7 for an extended
period of time, the probability of a La Niña
(wetter production season) increases.
The probability of the opposite El Niño
(dryer production season) phenomenon
increases when the SOI-values are lower
than -7 for an extended period of time.
The SOI-data for the past three seasons is
reflected graphically in Figure 1.
The probability of either an El Niño
or La Niña phenomenon on the basis of
SOI-figures, is confirmed by measuring
sea surface temperatures in the Nino 3.4
area, whereafter these temperatures are
compared with the long-term average
temperature.
These sea surface temperatures are
expressed as a norm by means of month-
ly Oceanic Niño Index (ONI) values. Every
monthly ONI-value is the 3-month average
of the sea surface temperature in the
Niño 3.4 area. Should 5 consecutive ONI-
values be warmer than 0.5° Celsius, an
El Niño phenomenon would be identified,
but should the ONI-values for 5 consecu-
tive months be cooler than -0.5° Celsius, a
La Niña phenomenon would be identified.
These values have been classified even
further over time to indicate the expected
intensity of an El Niño or La Niña phenom-
enon. The classification is done in 0.5°