TOPOGR APHICAL
El Niño: from
fire to f lood
El Niño phase
Occurs when the SOI records
sustained negative values (usually
below –8). El Niño is associated
with drier conditions over most of
Australia, particularly in the north
and east of the continent.EL NIÑOLA NIÑANEUTRALA
USTRALIA is a land “of droughts and
fl ooding rains” – our climate cycles from
one to the other, sometimes slowly,
sometimes quickly. The El Niño Southern
Oscillation (ENSO) is a major climatic infl uence
on rainfall in Australia and is the result of air and
ocean movements across the Pacifi c Ocean.
As warmer water fl ows eastwards, from Australia
to South America, air currents carrying rain-bear-
ing clouds move away from Australia out into the
central Pacifi c. This leads to drier months and
more droughts and bushfi res.The warm water
fl owing along the coast of Peru displaces cold cur-
rents carrying plankton, the food of anchovies.
Peruvian fi shermen fi rst recognised the pattern
because they hauled in much smaller catches at this
time. They named the event El Niño, or the boy
child, because it occurred at Christmas time.
El Niño events occur every 4–7 years, and usu-
ally last 12–18 months, peaking in December–
April. Higher air pressure over Australia is one of
the indicators. The ‘Southern Oscillation Index’
(SOI) measures the diff erence between pressure
in Darwin and Tahiti and turns negative during
El Niño. The reverse pattern, La Niña, is linked
to fl ooding rains: under this pattern warmer
waters move back towards Australia, as do the
trade winds and rain-bearing clouds.Long-term patterns
The ENSO Tracker records El Niño and
La Niña events using a three-tier system.
It monitors sea-surface temperatures,
winds, and the SOI, combined with climate
modelling to forecast the oscillations.Extreme events
Is there a correlation between El Niño and extreme
weather events? This graph plots Eastern Australia’s
most extreme weather events against the oscillations.La Niña phase
This occurs when the Southern
Oscillation Index (SOI), which
measures the air pressure
differential between Darwin and
Tahiti, records sustained positive
values (usually above +8). La Niña is
associated with wetter conditions over
much of Australia, particularly in the
north and east of the continent.El Niño and La Niña have a significant effect on
the Australian climate, but how do they work?STORY ÅSA WAHLQUIST ILLUSTRATION MICHAEL PAYNEArea affected
by La Niñal Niño phase
curswhen the SOIrecords
stained negative values (usually
ow – 8 ). ElNiño is associated
th drier conditionsover most of
stralia, particularly in the north
d east of the continent.much of Australia,particularly in the
north andeast of thecontinent.Walker CirculationTypical spring
positions of high
pressure systemsDarwinCooler water
than normalCold^ waterWarm^ water1980
1985 1990 1995ASH WEDNESDAY, SA/VIC
APR 1983SOUTH-EASTERN AUSTRALIA, NSW/VIC
1982– 83
EASTERN AUSTRALIA, QLD/NSW
1991–
WATERFALL, NSW
NOV 1980 EAST COAST, NSW
DEC 1994
SYDNEY, NSW
AUG 1986YEAR18 Australian GeographicArea affected
by El Niñoag0914_topoP19 - 19 2014-08-07T16:05:23+10: