APRIL 2008

Online
Geo file 569

Paul Warburton

I MPACTS OF EL NIÑO AND LA NIÑA

What are El Niño and La Figure 1: Pattern of El Niño, La Niña and neutral conditions 1950 to 2001
Niña?
2.0
El Niño and La Niña are amongst the
most powerful phenomena on Earth, Key
affecting the climate across more than La Niña

Strength of El Niño/La Niña event (El Niño index)

half the planet. El Niño (Spanish 1.5 El Niño
name for a male child) is used to refer Neutral
to a weak, warm current appearing
annually around Christmas along the 1.0
coast of Ecuador and Peru. El Niño
events occur every three to seven
years (Figure 1) and may last from 12 0.5
to 18 months. In recent decades there
have been several exceptional El Niño
events which have had almost 0
worldwide consequences. The term is
now linked to these stronger events.
0.5
In contrast to El Niño, La Niña
(female child) refers to an anomaly of
unusually cold sea surface 1.0
temperatures found in the eastern
tropical Pacific. A La Niña episode
may, but does not always, follow an El 1.5
Niño. 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000
Year

Causes of an El Niño
Source: The International Research Institute for Climate and Society
In the tropical Pacific, trade winds GeoFile Series 26 Issue 3
generally drive the surface waters Fig 569_01 Mac/eps/illustrator 11 s/s
NELSON THORNES PUBLISHING
westward (Figure 2). The surface Figure 2: Normal conditions in Artist:
the Pacific basin Illustration
David Russell
water becomes progressively warmer
going westward, because of its longer
North America
exposure to solar heating. El Niño is Asia
Polar jet
observed when the easterly trade Subtropical
winds weaken (Figure 3), allowing the jet
warmer waters of the western Pacific
to migrate eastward and eventually Warm
Strong trade
winds
reach the South American coast. The water
cool water normally found along the Low Equatorial currents (strong)
Cool
water Ecuador
coast of Peru is replaced by warmer pressure Peru
water. At the same time the area of Strong South
warmer water further west near Australia
High Peruvian America
pressure Current
Australia and Indonesia is replaced by
cooler water.
GeoFile Series 26 Issue 3
Figure 3: Conditions during an El Niño event
Fig 569_02 Mac/eps/illustrator 11 s/s
What is the difference NELSON THORNES PUBLISHING
between La Niña and El Artist: David Russell Illustration
Polar jet
Niño? Wetter than
average winter
Both terms refer to large-scale changes Subtropical
jet
in sea-surface temperature across the
Weak trade
central and eastern tropical Pacific. winds
Usually, sea-surface readings off South Pressure
increases
America’s west coast range from about Strong counter current Warm
15°C to 21°C, while they exceed 25°C Drier than
water

in the ‘warm pool’ located in the average

central and western Pacific. This Pressure Weak

warm pool expands to cover the decreases Peruvian
tropics during El Niño, but shrinks to Current

GeoFile Series 26 Issue 3

Geofile Online © Nelson Thornes 2008
Fig 569_03 Mac/eps/illustrator 11 s/s
NELSON THORNES PUBLISHING
Artist: David Russell Illustration
April 2008 no.569 Impacts of El Niño and La Niña

the west during La Niña. The El Niño Figure 4: Broad climate impacts of El Niño
Southern Oscillation (ENSO) is the
coupled ocean-atmosphere process Northern hemisphere winter
that includes both El Niño and La Key
Niña. Wet
Dry
Warm
What causes La Niña? 60°N

50°
Typically, a La Niña is preceded by a 40°
build-up of cooler than normal 30°
subsurface waters in the tropical 20°
Pacific. Eastward-moving 10°
atmospheric and oceanic waves help EQ
10°
bring the cold water to the surface 20°
through a complex series of events, 30°
still being studied. In time, the 40°
easterly trade winds strengthen, cold 50°S
upwelling off Peru and Ecuador 00° 20°E 40° 60° 80° 100° 120° 140° 160° 180° 160°W 140° 120° 100° 80° 60° 40° 20°
intensifies, and sea-surface
temperatures (SSTs) drop below
normal. During the 1988-89 La Niña, Northern hemisphere summer
SSTs fell to as much as 4°C below Key
normal. Both La Niña and El Niño Wet
Dry
tend to peak during the Northern Warm
Hemisphere winter. 60°N

50°

Impacts of El Niño 40°

30°
This article is far too short to cover 20°
the numerous impacts of both El 10°
EQ
Niño and La Niña. They vary both in 10°
type and spatially. Broadly, the 20°
impacts of La Niña are the opposite of 30°
those of El Niño, so we will consider 40°

those of La Niña more briefly. We will 50°S

consider the impacts moving 00° 20°E 40° 60° 80° 100° 120° 140° 160° 180° 160°W 140° 120° 100° 80° 60° 40° 20°
outwards from the countries
immediately affected, to those further
away. GeoFile Series 26 Issue 3
El Niño also leads to humanFig 569_04
deaths,Mac/eps/illustrator 11 s/s
diseases transmitted by mosquitoes,
NELSON THORNES PUBLISHING
Latin America injuries and homelessness. As such as malaria
Artist: David Russell Illustration and dengue fever.
The warm water that builds up off the populations grow and are Malaria transmission is particularly
coast of South America leads to concentrated in high-risk areas like sensitive to weather conditions. In
significant increases in evaporation coastal zones and cities, their normally dry climates, sudden heavy
and precipitation. 1982/83 saw one of vulnerability to catastrophe increases. rainfall can create puddles,
the most severe El Niños on record: Large shanty towns with flimsy providing good breeding conditions
over 2500mm of rain fell over a six- dwellings are often located on land for mosquitoes. Conversely, in
month period in Ecuador and subject to frequent flooding. In many normally very humid climates,
northern Peru, about 300 times the areas the only places available to poor droughts may turn rivers into strings
average figure. This led to devastating communities may be marginal land of pools, preferred breeding sites of
flooding that swept away people’s with few natural defences against other types of mosquito.
homes and caused extensive damage weather extremes. In 1997 Central
to farming. Ecuador and Peru suffered rainfall Indonesia and Australia
more than 10 times normal, which While South America has wetter
Under normal conditions, colder caused flooding, extensive erosion and conditions, south east Asia
water, rich in nutrients, upwells off mudslides with loss of lives, experiences the opposite. The colder
the coast of much of the west coast of destruction of homes and food water in the western Pacific reduces
South America. In an El Niño year supplies. Nearly 10% of all health evaporation, encouraging drier
this is replaced by warm water, less facilities in Peru were damaged. conditions. Eastern Australia endured
rich in nutrients, and consequently one of its worst-ever droughts in
there is a decline in plankton and Ecuador, Peru and Bolivia suffered 1982/83, resulting in a $2,000 million
other aquatic life. The fisheries serious malaria epidemics after loss in agricultural production (Figure
industry off the Pacific coast of South heavy rainfall in the 1983 El Niño. 5), as well as bushfires and dust
America lost about $290 million The epidemic in Ecuador was storms.
during the 1982/83 El Niño as catches, exacerbated by displacement of
particularly of anchovy, declined. The population owing to the flooding. Indonesia also had dry conditions in
loss of fish and plankton also caused The El Niño cycle is associated with 1982/83, and many died as a result of
the starvation of many seabirds. increased risks of some of the crop failure and famine. Human
Geofile Online © Nelson Thornes 2008
 April 2008 no.569 Impacts of El Niño and La Niña

error coupled with El Niño has led to Figure 5: Australian wheat yields and SOI index (SOI is a measure of the intensity
environmental disaster in Indonesia of an El Nino event)
and other south east Asian countries.
Logging companies in Indonesia 1.6 20
have been clearing areas of forest by
deliberately setting fire to them. 15
Normally, regular rainfall would 1.4
dampen down the flames and prevent
10
the spread of fires. El Niño has the
effect of stopping rains from reaching 1.2
Indonesia, so fires have spread out of

SOI (June – August)

5

Tonnes/hectare
control. Huge clouds of smoke have
caused unprecedented levels of smog, 1.0 0
and at times made the air in certain
areas of southeast Asia extremely –5
dangerous to breathe. There have 0.8
also been devastating effects on
–10
wildlife, with thousands of creatures
dying. 0.6
–15

Other parts of the world

El Niño also disrupts climate much 0.4 –20
further afield (Figure 4). Other areas 1948 1951 1954 1957 1960 1963 1966 1969 1972 1975 1978 1981 1984 1987 1990
also experience unusual amounts of Year
Wheat yield – SOI
precipitation. In 1982/83 there were
exceptional rainstorms in California,
Source: http://www.bom.gov.au/climate/glossary/elnino/elnino.shtml
and storms in China and in Mexico,
where the town of Guadalajara saw GeoFile Series 26 Issue 3
snow for the first time since 1881. sales of snow equipment like the huge forest
Fig 569_05 Mac/eps/illustrator 11 s/sfires. During 1982/83
Drier conditions also occur in parts snowmobiles were down byNELSONnearly THORNESEl Niño is said to have led to the
PUBLISHING
of India as the monsoon pattern is 35%. Skiing increased in theArtist:
WestDavid Russell
death Illustration
of some 2000 people
disrupted. Austria and parts of but fell in the Midwest. In the highly worldwide, and caused losses
central Europe experienced drought weather-sensitive energy sector, amounting to approximately $12
conditions, and forest fires burnt households and businesses saved $2-7 billion.
parts of south east Asia and Brazil. billion in heating costs, while energy
production and distribution Impacts of La Niña
In MEDCs there are more varied businesses suffered from reduced
Latin America
impacts caused by El Niño, largely sales.
Higher yields and thus greater
because there are more weather- and exports during cold events have had a
climate-sensitive industries (such as On balance, the effect of the 1997/98
positive influence on the fishing
agriculture, construction, energy El Nino in the US could well have
industry. For example, in 1996 the
distribution, and outdoor recreation). been an economic benefit, taking
anchovy and sardine catches
In the USA these account for nearly into account gains and losses across
increased, with a corresponding
10% of GDP. Weather and climate regions and industries. While
increase in exports. Cool ocean
indirectly affect an even larger economic impacts tend to cancel each
temperatures are generally associated
portion of the nation’s economy, other out at the national level, El
with increased catches of some
extending to sectors such as finance Nino does cause real economic losses
species such as anchovy.
and insurance, services, retail and such as storm damage or crop losses,
La Niña greatly impacts the health
wholesale trade, as well as which are not offset by gains
sector, because of the higher numbers
manufacturing. Some analysts elsewhere. These are losses that can’t
of bronchial diseases and respiratory
estimate that nearly 25% of US GDP, be prevented or reduced by a better
illnesses that occur, especially in
or $2.7 trillion, is either directly or forecast or mitigation. For example,
central and southern Peru where the
indirectly affected by weather and on average, El Niños result in
humidity is higher. Health problems
climate. agricultural losses approaching $2
also aggravate an already bad poverty
billion, or nearly 1-2% of total crop
and pollution situation.
El Niño affects important business output. In the 1997/98 El Niño,
variables like sales, revenues, and property losses were estimated at
employment in a wide range of nearly $2.6 billion. Fortunately, these La Niña is associated with severe
climate-sensitive industries and real losses are generally only a small drought conditions in coastal areas,
sectors. Overall, total US economic fraction of the economic impacts of as well as decreased temperatures.
impacts of the 1997/98 El Niño were El Niño. During normal years there is a
estimated to be on the order of $25 reasonable amount of rain in the
billion. These economic impacts lead The 1991/92 El Niño brought the mountainous areas of Peru, as a result
to both gains and losses among worst drought of the 20th century in of the easterly trade wind flow over
regions and within industries. For southern Africa, which affected the Andes. But there is no rainfall
example, department store sales were nearly 100 million people. The 1997 along the coastal regions, unlike the
up by 5-15% during the abnormally El Niño droughts hit Malaysia, situation during El Niño years.
warm winter in the Midwest, but Indonesia and Brazil, exacerbating
Geofile Online © Nelson Thornes 2008
April 2008 no.569 Impacts of El Niño and La Niña

Indonesia and Australia o

! n!ls! ions Encouraged by progress over the past
La Niña can bring some welcome decade, scientists and governments in
relief to areas that normally experience Since 1983, forecasts of the next many countries are working together
drier conditions. Rains in late 2005 rainy season have been issued each to design and build a global system for
and early 2006 brought relief to November, based on observations of observing the tropical oceans,
Australia, which had been gripped by winds and water temperatures in the predicting El Niño and other irregular
its worst drought in living memory tropical Pacific region and the climate rhythms, and making routine
since 2002. Australian farmers output of numerical prediction climate predictions readily available to
benefited from the best rain in 10 models. The forecasts are presented those who have need of them for
years, which fell throughout eastern in terms of four possibilities: planning purposes, much as weather
and southern grain-growing areas • near normal conditions; forecasts are made available to the
towards the end of April, exactly the • a weak El Niño with a slightly public today. The ability to anticipate
right time for planting of winter wetter than normal growing how climate will change from one year
grains crops. season; to the next will lead to better
• a full-blown El Niño with management of agriculture, water
The wetter conditions were welcomed flooding; and supplies, fisheries, and other
by farmers in Vietnam, the world’s • cooler than normal waters resources. By incorporating climate
largest robusta coffee producer and the offshore, with higher than predictions into management
second-largest exporter of rice. Heavy normal chance of drought. decisions, people are becoming better
rains associated with La Niña can also adapted to the irregular rhythms of
bring problems, though. Oil palm, Once the forecast is issued, farmers’ climate.
rubber, coffee and cocoa plantations representatives and government
can all experience reduced crops, and officials meet to decide on the Finally, a word of caution. Climate is
rice fields experience too much appropriate combination of crops to very complex and unpredictable and it
rainfall and be flooded. In late 2005 sow in order to maximise the overall is still a subject where there is a huge
into early 2006, the Philippines, the yield. Rice and cotton, two of the amount of ongoing research. The
world’s largest coconut oil shipper, primary crops grown in northern media often make links between
was hit by La Niña and experienced Peru, are highly sensitive to the extreme weather events and El Niño
above-average rainfall. The heavy quantities and timing of rainfall. and La Niña; some may have a sound
rains caused mudslides, entombing a Rice thrives on wet conditions scientific basis, while others merely
community of 1,800 in Guinsaugon on during the growing season followed make eye-catching headlines. Further
Southern Leyte province, about by drier conditions during the study is needed and patterns need to
675km (420 miles) south east of ripening phase. Cotton, with its be clearly established so that we can
Manila, in February 2006. deeper root system, can tolerate drier make statements with increasing
weather. Hence, a forecast of El confidence.
Other parts of the world Niño weather might induce farmers
In the US, winter temperatures are to sow more rice and less cotton than s! ef!l so!re
! s of infor!i! on
warmer than normal in the south-east in a year without El Niño.
and cooler than normal in the north- http://ess.geology.ufl.edu/usra_esse/
west during a La Niña year. Snow and ENSO_Impacts.html
Other countries that have taken http://www.atmos.washington.edu/g
rain is experienced on the west coast, similar initiatives include Australia,
and unusually cold weather in Alaska. cg/RTN/rtnt.html
Brazil, Ethiopia, and India. http://www.yptenc.org.uk/docs/facts
There is also a higher than normal Although tropical countries have the
incidence of hurricanes in the heets/env_facts/el_nino.html
most to gain from successful http://www.pmel.noaa.gov/tao/elnino
Atlantic. La Niña effects are more prediction of El Niño, for many
pronounced during the Southern /nino-home.html#
countries outside the tropics, such as Animated explanation of El Nino
Hemisphere winter (July-August), Japan and the United States, more
when one can observe lower than http://www.guardian.co.uk/flash/0,,6
accurate prediction of El Niño will 41890,00.html
average temperatures. For example, a also benefit strategic planning in
few years with low temperatures Health aspects of El Nino
areas such as agriculture, and the http://www.who.int/mediacentre/facts
(around 12°C), and rice crops are badly management of water resources and
affected. However, cotton production heets/fs192/en/index.html
reserves of grain and fuel oil.
experiences an increase of 45% during
cold event years. This actually took
place in 1963, 1964 and 1996. Focus Questions
ENSO also has an influence on 1. Classify the positive and negative impacts of El Niño events in two
hurricane strikes on US and separate tables. Use the following headings: Climatic, Other environmental,
Caribbean shores. During La Niña Economic, Social.
periods, hurricane and tropical storm
landfalls are twice as common over 2. Describe and explain the trends shown in Figure 5.
much of the Caribbean and Gulf of
Mexico. Again the recent active 3. Outline how El Niño and La Niña could affect tourism.
Atlantic hurricane seasons of 1998-
2001 illustrates this. El Niños tend to 4. ESSAY
suppress tropical cyclones. Examine the effects of an El Niño cycle on the environment with reference
to different areas of the world.

!ofil! !nlin! ! N!lson !orn!s 2008