GRAIN BROKERS
Graph 1: Rainfall distribution during weak El Niño years for the western production area.
Source: Compiled by Thys Grobbelaar
Graph 2: Average cumulative rainfall distribution during weak El Niño years for the western
production area.
Source: Compiled by Thys Grobbelaar
by lower yields. Should the actual yields
for the western production area (sensitive
for El Niño events) be compared, the aver-
age yield since the 1919-20 season until
the 2017-18 season was 2.43mt/ha during
La Niña years, 1.56mt/ha during El Niño
years and 1.9mt/ha during neutral seasons.
Should these averages only be calculated
from the 1983-84 season, then La Niña
years yielded 3.72mt/ha, El Niño years
2.68mt/ha and neutral years 3.18mt/ha.
However, when only taking the average
of the weak El Niño years into account,
the situation looks different. The average
yield during the 10 weak El Niño seasons
as indicated in Table 1 is 2.24mt/ha,
which is better than the long-term average
of neutral years. This average for the weak
El Niño years since 1983-84 was 3.54mt/
ha which, once again, is better than the
yield during neutral years over the same
period. It therefore becomes evident that
weak El Niño years do not necessarily
translate to below average yield realisa-
tions. This yield expectation can, how-
ever, be linked to cumulative rainfall and
the distribution of rainfall as indicated in
Graph 1 and Graph 2.
Rainfall during weak El Niño years does
not necessarily indicate below average
rainfall. The average cumulative rainfall
during these seasons was 524.7mm com-
pared to the long-term cumulative average
of 553.8mm. Looking at the distribution
of rainfall in Graph 1, it is evident that
the variance from the long-term average
for every month from June to June the
next near, is significantly smaller from
September to December with more sig-
nificant variances from January to March.
In fact, the average rainfall for September
to December in weak El Niño years, was
higher than the long-term average rainfall
for these months. The average rainfall from
January to March during the weak El Niño
years is, however, below the long-term
average rainfall, which could indicate that
weak El Niño years could result in lower
rainfall during the traditional midsummer
drought period. Should the average rainfall
be indicated in a cumulative manner as in
Graph 2, the variance in respect of rainfall
distribution becomes more evident.
To summarise, the objective of this
article is not to make a prediction for
the 2018-19 season in respect of rainfall
expectations. The information contained
herein is based on actual historic realisa-
tion of weather phenomena and models
tested over time. The deduction which
can be made from the expectations is
that the production season will proba-
bly be characterised as a weak El Niño
season. This type of El Niño season is
not necessarily characterised by weak,
below average yields in the more sensitive
western production area and cumulative
rainfall does not vary significantly from the
long-term average rainfall. It is striking,
however, that the distribution of rainfall
indicates more favourable rainfall patterns
during the planting period of September
to December, but also that rainfall may
be below average for the traditional mid-
summer drought period. In view of this
deduction it would always be sensible for
producers to adjust planning in respect
of planting and plant date distribution as
to address the potential midsummer risk.
However, every season is unique and the
development of the current season is no
exception. Every producer will have to
determine his own risks and make sure
that available soil moisture is adequate
before a planting decision is made.
SENWES SCENARIO | MIND-SHIFT 2019
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