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UNIVERSITY OF NAIROBI
Department of Meteorology
STATUS OF THE 2015 EL NIÑO EVENT IN KENYA
Opijah, F.J., N. J. Muthama, C. Oludhe, G. O. Ouma and A. O. Opere
Issued Friday, 27 November 2015
What is El Niño?
Print, electronic and social media in East Africa have
portrayed El Niño as a condition with exceptionally
heavy rains, perhaps because of the phenomenal
occurrence in 1997/98. However, El Niño is not
always associated with heavy rains in East Africa. As a
matter of fact, some of the wettest years on record in
East Africa (the classic example of which was 1961)
were not linked to El Niño!
The phrase El Niño (pronounced as El Ninyo) literally
means “the boy child”, the shortened form for El
Niño de Navidad, which means
The Boy Child of
Christmas. This phrase was coined by fishermen in
Latin America who observed that during certain years
around Christmas time the fish catch was adversely
affected by warm ocean waters, which they
associated to spiritual forces.
During El Niño events, a warm ocean current flows
off the coast of northern South America in the south-
eastern Pacific Ocean. This warm current, which
results from weakened surface easterly winds, is
often accompanied with decreased upwelling of
ocean water and reduced upward transport of
plankton that is necessary for the countries’ thriving
fish industry.
El Niño is a fairly frequent phenomenon with a rate of
recurrence of one every three to seven years.
How El Niño Influences Rainfall in East
Africa
Global oceans continually interact with the
atmosphere in complex non-linear feedback
processes referred to as coupling. The drag of winds
on the ocean surface induces ocean waves and
changes in sea surface temperatures, which
subsequently generate pressure gradients that
govern the atmospheric motions. Changes in ocean
temperatures over the Pacific Ocean sometimes
coincide with higher or lower than normal ocean
temperatures over the Indian Ocean and altered
atmospheric systems, which is referred to as the El
Niño-Southern Oscillation (ENSO) phenomenon.
These complex interactions between distant places
are termed as teleconnections.
For El Niño to influence the rainfall over East Africa,
its occurrence should be in agreement with the Inter-
tropical Convergence Zone (ITCZ) and many other
systems that control the weather over the region.
More often than not, warm south-eastern Pacific
Ocean temperatures (El Niño) are associated with
warm waters in the western Indian Ocean near the
coast of East Africa. When the warming of the
western Indian Ocean is accompanied by cooler
ocean temperatures in the eastern Indian Ocean
(near the Indonesia/Malaysia maritime continent),
this phenomenon is referred to as the Indian Ocean
Dipole (IOD). A well-developed IOD was associated
with heavier than normal rains over East Africa in
1961, 1977, and 1997; but 1961 was in fact an ENSO
neutral year (i.e., neither El Niño nor La Nina, the
antithesis of El Niño)!
El Niño does not necessarily translate into heavy
rainfall for the entire equatorial East Africa region
(Ogallo, 1994). Statistically speaking, El Niño accounts
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for just 36% to 46% of the variability of rainfall across
the counties in Kenya (Muthama et al., 2013).-The
“short rains” season (from October to December) is
significantly and positively influenced by the El Niño
system (Muthama et al., 2013).
It takes some time for different oceans and
atmospheric systems to adjust in response to the El
Niño phenomenon. The patterns and impacts of
different El Niño events are never exactly the same.
Current Status and Projected Trends of the
2015 El Niño
The 2015 El Niño is very similar to that which was
observed in 1997 in many respects; being slightly
superior with regard to its areal spread (Figure 1), but
slightly inferior in respect of its intensity (Figure 2).
Figure 1: The strengthening El Niño with each passing month
showing striking similarity between the 2015 sea surface height
anomalies and 1997. (Source: NASA)
Most global models indicate that the 2015 El Niño
will reach its peak during the Northern Hemisphere
winter (November-February) season, persist into
spring (March-May) season, and transit to ENSO-
neutral conditions by June 2016. The western Indian
Ocean is expected to remain warm (i.e., a positive
IOD index) until December. There is a high probability
of wet conditions persisting into the New Year over
western and central (including Nairobi) regions, and
some counties in southern and coastal Kenya.
Impacts Associated with El Niño in Kenya
In view of the projected patterns of El Niño in the
Pacific Ocean and the warm currents in the western
Indian Ocean, we expect the ongoing rains in East
Africa to impact many areas in Kenya, which is likely
to adversely affect the physical infrastructure,
including the road, air and rail transport networks;
buildings, and telecommunications. There are
possibilities of the outbreak of diseases like malaria,
cholera, and dysentery in flood-prone areas of the
country. Rift Valley Fever outbreaks have also been
associated with ENSO conditions in the past and
there is need to take precautions in good time to
curb such outbreaks. Heavy rains may present various
challenges and opportunities to farmers across the
different counties, forestry, the hydropower energy
sector, communities that experience domestic water
shortfalls, and all sectors of the economy that
depend on water supplies, but only if the water is
harnessed and stored properly.
SST Anomalies in Equatorial Pacific
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0
0.5
1
1.5
2
2.5
DJF JFM FMA MAM AMJ MJJ
JJA
JAS ASO SON OND NDJ
Month Cluster
SS
T An
om
aly
1961
1969
1982
1987
1997
2010
2015
Figure 2: Trends of sea surface temperature (SST) anomalies for
various years in 2014/2015/2016, with positive values in excess
of 0.5 points indicating El Niño (Note that 1961, the wettest year
on record, was ENSO neutral). (Source: plotted using CPC data)
References
Muthama, N.J., J.K. Njeri and M.M. Manene (2013).
The influence of El-Nino Southern Oscillation on
seasonal rainfall over the 47 counties of Kenya.
International Journal of BioChemiPhysics, 21, 53-
63.
Ogallo, L.A. 1994. Validity of the ENSO-Related
Impacts in Eastern and Southern Africa. In M.
Glantz (ed.). Usable Science: Food Security, Early
Warning, and El Niño, pp. 179–184. Proceedings
of the Workshop on ENSO/FEWS, Budapest,
Hungary, October 1993. UNEP, Nairobi; and
NCAR, Boulder, Colorado.