GRAIN BROKERS
El Niño years
What happened in the past?
This article is the third in a series where we look at the background and development of
ENSO (El Niño Southern Oscillation) events. The previous edition looked at the specific
classification of ENSO in the form of a weak El Niño event.
By Frans Dreyer
Manager: Senwes Grain Brokerage
O
ne of the findings in the pre-
vious article was that history
indicates that rainfall during
weak El Niño years may
even be above average during the planting
period from September to December, but it
may change to below average cumulative
rainfall from January to March during the tra-
ditional mid-summer drought period. Rainfall
until the end of February once again con-
firmed the unique nature of every production
season. Figure 1 effectively reflects the
opposite trend in respect of rainfall until the
end of February 2019, with below average
rain which realised during the pre-season
period. This realisation could, however,
mean that the intensity of the existing weak
El Niño even may be stronger than initially
expected. It would therefore be sensible to
specifically look at the historic impact of a
stronger El Niño season on rainfall and the
concomitant yield.
A strong to very strong El Niño event is
identified when sea surface temperatures
are warmer than normal, but specifically
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SENWES SCENARIO | AUTUMN 2019
Figure 1: Rainfall comparison.
above a certain degree Celsius band. Sea
surface temperatures are expressed as a
norm by means of monthly Oceanic Nino
Index (ONI) values. Every monthly ONI-
value is the 3-month average of the sea
surface temperature in the Niño 3.4 area.
This classification was sub-divided over time
to indicate the expected intensity of an El
Niño or La-Niña event. The division is made
Source: Thys Grobbelaar
in 0.5° Celsius intervals and a strong El Niño
is indicated when sea surface temperatures
are 1.5° Celsius warmer than normal. This
classification makes it possible to categorise
previous seasons according to the type
of season experienced, as summarised in
Table 1.
Looking at El Niño and La-Niña events
over the long term, the actual impact