Niña is defined by
unusually cold ocean
temperatures in the
equatorial Pacific. It’s
caused by a build-up of very cool
water in the tropical Pacific, which
is brought to the surface by
easterly trade winds and ocean
currents. This upsurge of water
causes sea-surface temperatures
in areas near South America to
drop drastically.
La Niña can trigger changes in
rainfall patterns, atmospheric
circulation and atmospheric
pressure, having dramatic effects
on the global climate. La Niña
events are associated with
cataclysmic flooding in Northern
Australia. In 2010, they resulted in
the worst flooding in Queensland’s
history, causing more than two
billion Australian dollars’ worth of
damage and requiring the
evacuation of over 10,000 people.
La Niña does have some positive
effects, however, often boosting
the South American fishing
industry due to the upwelling of
nutrient-rich waters.
Although our understanding of
La Niña has grown, forecasting it is
still difficult, even when
combining the latest satellite and
marine buoy data. With such a
global impact, every effort is being
made to find a way to predict this
age-old phenomenon.
The devastation caused by La Niña in
Queensland was unprecedented;
thousands of homes were destroyed
What happens during La Niña?
See how a period of cooler sea temperature can have far-reaching effects
Walker circulation cell
This is the name given to the airflow seen
in the tropics during normal conditions
and La Niña, but is reversed during El Niño.
Normal rainfall
Rainfall in this location is
common, but is less frequent
than during La Niña.
Normal trade winds
These blow in the same direction
during La Niña, but weaken or even
reverse during El Niño (where ocean
temperatures are warmer than usual).
Moist air rising
Moist air rises from the
warm water but cools once
it reaches South America.
La Niña trade winds
During La Niña the equatorial
trade winds become even
stronger, warming Australian
waters as they blow east to west.
Increased rainfall
Rainfall increases in the western
Pacific due to low-pressure
zones, but decreases over the
eastern Pacific.
Stronger
upwelling
The stronger
upwelling around
South America
causes deep, cold
water to rise to the
surface, providing
nutrient-rich
waters that boost
fish populations.
Warmer Australia
In Australia, sea
temperatures are found to
be warmer than average
during La Niña.
Equatorial
thermocline
La Niña results in the
equatorial thermocline
steepening, due to
upwelling in South
American waters.
Cooler South America
La Niña causes the sea
temperature around South
America to drop, cooling
by 3 to 5°C (5.4 to 9°F).
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